Ac 91-85a RVSM
Ac 91-85a RVSM
Ac 91-85a RVSM
Department
of Transportation
Federal Aviation
Administration
Subject: Authorization of Aircraft and
Operators for Flight in Reduced
Vertical Separation Minimum
(RVSM) Airspace
Advisory
Circular
Date: 7/21/16
Initiated by: AFS-400
AC No: 91-85A
Change:
This advisory circular (AC) applies to all Operators conducting Reduced Vertical Separation
Minimum (RVSM) operations. The AC can be used to obtain an initial operational authorization,
or amend an existing, operational authorization. The AC appendices include supportive
information relating to RVSM airworthiness certifications, training programs, operating practices
and procedures, RVSM operations in oceanic and remote continental airspace, and review of
height-keeping parameters.
This AC describes acceptable means, but not the only means, for an Operator to obtain
authorization to conduct flight in airspace or on routes where RVSM is applied. The advisory
material contained in this AC has been substantially modified since the AC was issued in its
original form in 2009.
John Barbagallo
Deputy Director, Flight Standards Service
7/21/16
AC 91-85A
CONTENTS
Paragraph
Page
1.2
1.3
1.4
1.5
1.6
What Do Some of the Capitalized Terms Used in This AC Mean? ............................ 1-2
Why are RVSM Authorizations Required, and How has the Authorization
Process Changed Since RVSM Authorizations were Initially Implemented
on a World-Wide Basis?.............................................................................................. 2-1
2.2
2.3
2.4
2.5
3.2
3.3
3.4
Who is the Proper Party to be the Applicant for, and the Operator Under, an
RVSM Authorization? ................................................................................................. 3-3
3.5
Who is a Responsible Person, and What Duties Does This Person Fulfill, Under
an RVSM Authorization? ............................................................................................ 3-4
3.6
What is the First Step an Applicant May Consider Taking When Applying for an
RVSM Authorization? ................................................................................................. 4-1
4.2
What are the Applicable Steps and Information Required to Seek an RVSM
Authorization? ............................................................................................................. 4-1
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AC 91-85A
What is the General Process the FAA will Follow Upon Submission of the
Request for an RVSM Authorization or Amended Authorization? ............................ 5-1
5.2
What are the Applicable Forms of the RVSM Authorization Documents? ................ 5-1
5.3
What are the Conditions That Would Require the Removal of an RVSM
Authorization? ............................................................................................................. 5-2
5.4
Scenario 1 ...........................................................................................................C-2
Figure C.1-2.
Scenario 2 ...........................................................................................................C-3
Figure C.1-3.
Figure C.1-4.
Figure C.1-5.
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AC 91-85A
Figure C.1-6.
Figure C.1-7.
Table A.2-1.
Table A.8-2.
Table A.8-3.
Residual Static Source Error (Aircraft with Avionic Static Source Error
Correction)....................................................................................................... A-21
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AC 91-85A
CHAPTER 1. INTRODUCTION
1.1
What is the Purpose of This Advisory Circular (AC)? This AC is not mandatory and
does not constitute a regulation. This AC describes an acceptable means, but not the only
means, for an Operator to obtain an initial operational authorization, or amend an existing
operational authorization to conduct flight in airspace or on routes where Reduced
Vertical Separation Minimum (RVSM) is applied. Additionally, this AC provides
information on RVSM performance specifications, obtaining and maintaining RVSM
airworthiness certification for aircraft, specific elements of an RVSM authorization, and
policy and procedures for RVSM operations. RVSM airspace is any airspace or route
between flight level (FL) 290 and FL 410 inclusive where aircraft are separated vertically
by 1,000 ft (300 m).
1.2
Who Does This AC Apply To? This AC applies to operators who want to apply for
authorization to conduct operations in RVSM airspace.
1.3
What Does This AC Cancel? This AC cancels AC 91-85, Authorization of Aircraft and
Operators for Flight in Reduced Vertical Separation Minimum Airspace, dated
August 21, 2009, which provided guidance on aircraft and Operator approval for
operating in RVSM airspace.
1.4
1.5
Part 43;
Part 121;
Part 125;
Part 129;
Part 145.
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1.6
AC 91-85A
What Do Some of the Capitalized Terms Used in This AC Mean? For the purposes of
efficiency and consistency, when the various capitalized terms below are used in this AC,
then they have the following meanings. Or you can find their meanings in the paragraphs
specifically mentioned in the definition.
Operator. The person who should be the RVSM authorization applicant and holder.
See paragraph 3.4 for a detailed discussion on who is and is not the correct person to
be designated as an Operator for the purposes of holding an RVSM authorization.
RVSM-Compliant Aircraft. An aircraft the FAA has found to comply with the
requirements of part 91 appendix G, section 2, for the purposes of conducting RVSM
operations. (See paragraph 3.2.)
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AC 91-85A
CHAPTER 2. AUTHORIZATION OVERVIEW
2.1
Why are RVSM Authorizations Required, and How has the Authorization Process
Changed Since RVSM Authorizations were Initially Implemented on a World-Wide
Basis?
2.1.1
2.1.2
RVSM Implementation. The FAA implemented RVSM in all of the airspace in the lower
48 states, Alaska, the San Juan flight information region (FIR), Gulf of Mexico, and
Atlantic High Offshore Airspace on January 20, 2005. To safely operate in RVSM
airspace, all aircraft needed to be configured and inspected to ensure the applicable
RVSM performance requirements were complied with.
2.1.3
Reason for Change. Because the RVSM requirements were new to most Operators when
they were first put into place, those aircraft and Operators had to be reviewed by the FAA
as a first instance in order to ensure the basic requirements were being met. Since
domestic RVSM implementation occurred in 2005, most existing aircraft have since been
configured for compliance or have been newly manufactured in compliance with these
requirements and have been reviewed at least once by the FAA. Also, most Operators
have now developed pilot knowledge and/or training programs previously reviewed at
least once by the FAA. Therefore, the initial one-size-fits-all authorization approach
initially adopted in 2005, which assumed all Operators, aircraft, and pilot training
programs had never been reviewed before, is no longer warranted with respect to the
processing of new or amended RVSM authorizations.
2.1.4
FAA Order 8900.1 Guidance. In recognition of these changes, the FAA amended those
portions of Order 8900.1, Flight Standards Information Management System (FSIMS),
addressing the issuance of RVSM authorizations on January 24, 2014, in order to create
guidelines improving efficiency in the authorization process. Based on the changes
highlighted above, there is recognition of two key elements for a RVSM authorization.
The two key elements are an RVSM-Compliant Aircraft and properly trained pilots who
have met applicable RVSM-Knowledgeable Pilots requirements. The guidance was
created along with a decision matrix (see paragraph 2.4) to allow the FAA to more
efficiently direct attention to only the RVSM Authorization Elements requiring initial
review. The guidance allows the reviewing safety inspector to accept previously reviewed
RVSM Authorization Elements without further examination, so long as the appropriate
information has been provided to the FAA as part of the application process.
2.1.5
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2.2
2.2.1
Altimetry System Error (ASE). RVSM compliance proceeds on the basis of FAA
certification of the altimetry system design and implementation, which is typically
conveyed through type certification (TC) or Supplemental Type Certification (STC). It is
generally acknowledged that one aspect of the design is an instrumentation system error
budget allowing for a difference between the static pressure sensed and the actual altitude
flown. This difference is not seen on the displayed altitude in the flight deck and it is not
in the Mode C or Mode S reply from the aircraft transponder. Therefore, it is invisible to
the pilot, to air traffic control (ATC), and to the Traffic Alert and Collision Avoidance
System (TCAS).
2.2.2
Height Monitoring. Aircraft instructions for continued airworthiness (ICA) are designed
to keep the altimetry system error (ASE) to within the limits of the error budget
throughout the flight envelope. These limits vary between aircraft types and within a
type, from airframe to airframe. Regardless, even with attention to continuing
airworthiness, there are factors that can affect the ASE significantly and can go
undetected in routine operations. Thus, through continuous sampling, the FAA
independently monitors altimetry system performance of airframes in the population of
aircraft participating in RVSM operations. This sampling is accomplished through
operational monitoring flights using either special equipment brought on board the
aircraft or through separate ground-based height monitoring systems. See
paragraph 3.6.4.
2.2.3
RVSM Performance. Appendix A gives details regarding the ASE performance demands
for safely operating in RVSM airspace.
2.3
What are the RVSM Authorization Elements? The definition and use of the two
RVSM Authorization ElementsRVSM-Compliant Aircraft and RVSM-Knowledgeable
Pilotsarose from recognizing these are the two basic building blocks needed to meet
the technical requirements in order to safely conduct operations in RVSM airspace. These
elements provide the basis for developing the RVSM Matrix (see paragraph 2.4). Once
the FAA has found an aircraft to be RVSM-compliant, if it is properly maintained and
monitoring shows that its performance has not degraded over time, the aircraft remains
RVSM-compliant. Under these conditions, it is inefficient for the FAA to have to review
the status of that aircraft again (as if it had never been compliant) when a subsequent
Operator requires his/her/its own authorization to operate that aircraft in RVSM airspace.
By specifically defining these two elements and putting certain safeguards into place
(such as compliance statements by subsequent Operators), the FAA could then create the
RVSM Authorization Matrix in order to streamline the process of reviewing and issuing
new RVSM.
2.4
What is the RVSM Authorization Matrix? The RVSM Authorization Matrix (or
simply the Matrix) is a tool created to assist Operators and the FAA in determining the
typical documentation needed for application and which RVSM Authorization Elements
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AC 91-85A
approval action the applicant is seeking. The full Matrix is provided in Chapter 4, but the
following is a summary of how the Matrix works.
2.4.1
2.4.2
2.4.3
When Does Authorization Group III Apply? Authorization Group III applies to
applicants for new RVSM authorizations not based on any existing RVSM Authorization
Elements. If neither Authorization Group I nor II apply, the applicant should submit
sufficient evidence to show its ability to comply with each of the RVSM Authorization
Elements.
2.4.4
What Additional Issues Should an Applicant be Aware of When Using the Matrix? The
FAA has created inspector guidance in order to allow for the most efficient processing of
an RVSM authorization without sacrificing operational safety. While a safety inspector
may rely on that guidance in issuing new or amended RVSM authorizations, applicants
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AC 91-85A
CHAPTER 3. RVSM AUTHORIZATION ELEMENTS
3.1
What is the Background Behind Using the RVSM Authorization Elements to Apply
for an RVSM Authorization? The RVSM authorization process recognizes two key
elements of any RVSM authorizationan RVSM-Compliant Aircraft and properly
trained pilots who have met applicable RVSM-Knowledgeable Pilots requirements. An
Operator must demonstrate to the FAA both of these elements exist to be authorized to
operate in RVSM airspace. All of these RVSM Authorization Elements are described in
this chapter.
3.2
3.2.1
3.2.2
3.2.1.1
3.2.1.2
If the aircraft was made RVSM-compliant through a SB, STC, or SL, or other
appropriate methods, the RVSM-compliant date will be listed in the airframe
maintenance log. Include copies of the maintenance record return to service
entry.
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AC 91-85A
3.2.3
3.3
3.3.1
The following are acceptable means for the Operator to show the FAA its
pilots have adequate knowledge of the RVSM operating practices and
procedures: 14 CFR part 142 training center certificates without further
evaluation; certificates documenting completion of a course of instruction
on RVSM policy and procedures; and/or an Operators in-house training
program.
Note: The FAA, at its discretion, may evaluate a training course prior
to accepting a training certificate.
3.3.1.2
For an applicant who operates under part 91 subpart K (part 91K), 121, or
135, in addition to meeting the adequate knowledge requirements for part 91
operators, that applicant will need to provide sufficient evidence of initial and
recurring pilot training and/or testing requirements as well as policies and
procedures allowing the operator to conduct RVSM operations safely as
required in part 91 appendix G, section 3(b)(2) and (3) in order to demonstrate
they are using RVSM-Knowledgeable Pilots. Therefore, part 91K, 121, and
135 Operators should submit training syllabi and other appropriate material to
the FAA showing operating practices and procedures and training items
related to RVSM operations are incorporated in initial and, where warranted,
recurrent training programs. (Training for dispatchers should be included,
where appropriate.)
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3.3.2
AC 91-85A
3.3.2.2
3.4
Who is the Proper Party to be the Applicant for, and the Operator Under, an
RVSM Authorization?
3.4.1
Who is the Correct Person to Apply for and Have Issued the RVSM Authorization?
The person exercising operational control of the aircraft during the operation requiring an
RVSM authorization is the proper person to be the applicant for that authorization. It is
important to note it is the RVSM applicants responsibility to submit a request for RVSM
authorization in the name of the person having operational control of the aircraft, not the
responsibility of the FSDO or a specific ASI to make such a determination. The
following general information may be useful in assisting the RVSM applicant in
determining if the appropriate party has been properly designated as the legal Operator
with respect to the RVSM authorization request:
1. For commercial and fractional ownership program operations conducted under
parts 91K, 121, 125, and 135, the authorization applicant and holder should be
the operating certificate holder, air carrier certificate holder, or fractional
ownership program manager, in which event the authorization will be issued
in the form of an appropriate operations specification (OpSpec) or
management specification (MSpec).
2. For non-commercial operations conducted under part 91 and part 125
(A125 LODA holders), the authorization applicant and legal Operator should
normally be one of the following persons, in which event the authorization
will be issued in the form of an appropriate letter of authorization (LOA):
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AC 91-85A
Note: The legal Operator will generally not be: an owner trustee not operating the
aircraft for its own business, a management company that has not accepted a
transfer of operational control from the Operator, or a holding company or bank
that holds title to the aircraft solely for the purpose of leasing or transferring
operational control of the aircraft to other persons.
3. It is both possible and common to have multiple Operators for part 91, 91K,
and/or 125/135 aircraft over a short period of time and on a non-exclusive
basis (for example, multiple dry leases for the use of any one aircraft can be in
place at one time). In such instances, each individual Operator is required to
have an appropriate RVSM authorization issued in its own name in order for
that Operator to have access to RVSM airspace. For example, if an aircraft
owner elects to lease the aircraft to a part 135 certificate holder for charter
operations but retain operational control of the aircraft for its own part 91
flights, then the part 135 certificate holder will hold its RVSM authorization
under its OpSpec for those charter operations, and the owner will
simultaneously hold a separate RVSM LOA for its own part 91 operations.
3.5
Who is a Responsible Person, and What Duties Does this Person Fulfill, Under an
RVSM Authorization?
3.5.1
Who is a Responsible Person and How Does this Relate to RVSM Authorizations?
For part 91 RVSM applicants, the application for authorization to operate within RVSM
airspace must include the designation of a Responsible Person, and may further include
the designation of a separate RVSM-POC, as follows:
3.5.1.1
The Operator should designate a person(s) who has the legal authority to sign
the RVSM authorization on behalf of the Operator and who has adequate
knowledge of RVSM requirements, policies, and procedures. That person may
be the individual person who will be the Operator, or, if the Operator is a legal
entity, then an officer or employee of that entity, or a separate person who that
individual person or entity has contracted with in order to act on behalf of the
individual person or legal entity with respect to the RVSM authorization.
3.5.1.2
The Operator should also designate a person(s) to act as a contact person who
has actual day-to-day knowledge of the RVSM-Compliant Aircraft operations
and RVSM airworthiness status the FAA may contact to gather such
information when such a need arises.
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AC 91-85A
3.5.1.3
The Operator may use one individual to fulfill both roles as described in
paragraphs 3.5.1.1 and 3.5.1.2, or the Operator may elect to designate separate
persons to fulfill these roles.
3.5.1.4
3.5.1.5
If the Operator chooses to use separate individuals, then the person fulfilling
the role described in paragraph 3.5.1.2 will be designated as the
RVSM-POC. In such event, the separate person designated as the
RVSM-POC (i.e., someone who has not also been designated as a Responsible
Person) will not have any authority to sign the RVSM authorization on behalf
of the Operator. Additionally, if an Operator has designated a separate
RVSM-POC, then that is the individual the FAA should first contact with
respect to the Operators RVSM-Compliant Aircraft operations and RVSM
airworthiness status.
3.5.1.6
3.5.1.7
3.6
What Other Issues Should be Addressed by Applicants with Respect to Requests for
RVSM Authorizations?
3.6.1
RVSM Configuration List. The applicant should provide a configuration list, for the
applicable aircraft, which details components and equipment relevant to RVSM
operations. (See Appendix A for a discussion of equipment for RVSM operations.)
3.6.2
3.6.3
3.6.4
RVSM Height Monitoring. RVSM height monitoring was implemented with the
establishment of RVSM airspace to ensure implementation and continued operation of
RVSM meets safety objectives. Compliant height-keeping performance of airplanes is a
key element in ensuring safe operations in RVSM airspace. RVSM is a performance3-5
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AC 91-85A
based operation requiring ongoing, independent monitoring to ensure that the RVSM
airspace airplane population adheres to stringent altimetry system requirements.
Note 1: The requirement for operational flight monitoring may not be included
in the Operators ICA.
Note 2: For a detailed discussion of RVSM height monitoring, see the RVSM
Height Monitoring Guide for U.S. Operators on the FAAs RVSM Web page in
the Monitoring Requirements and Procedures section.
3.6.4.1
3.6.4.2
3.6.4.3
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AC 91-85A
current version of this chart can be found on the FAAs RVSM
Web page in the Monitoring Requirements and Procedures section.
Note: An Operator that is unable to meet the minimum height
monitoring requirements within the specified time frame should
contact the responsible CHDO/CMO/FSDO/IFO prior to exceeding
the specified time frame. (See paragraph 3.6.4, Note 1.)
3.6.4.4
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AC 91-85A
3. For North American Operators, the database can be accessed from
the FAA RVSM Web site under the section RVSM Documentation
or on the FAAs NAARMO website at:
https://www.faa.gov/air_traffic/separation_standards/naarmo/rvsm
_approvals/.
3.6.4.6
3.6.5
3.6.5.2
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3.6.5.3
3.6.5.4
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What is the First Step an Applicant May Consider Taking When Applying for an
RVSM Authorization?
4.1.1
4.1.2
4.2
What are the Applicable Steps and Information Required to Seek an RVSM
Authorization? Prior to making a request for service, each applicant should review the
information provided in Chapter 3 as well as the RVSM decision Matrix in Figure 4-1 to
determine if the applicant should apply procedures for Authorization Group I,
Authorization Group II, or Authorization Group III. Each of these groups is summarized
in paragraph 4.2, with the RVSM-Decision Matrix (Figure 4-1) provided for detailed
examples and information for the application process.
Note: The written request discussed in paragraphs 4.2.1.2, 4.2.2.2, and 4.2.3.2 is
your letter to the CHDO requesting service. Using the RVSM Decision Matrix in
Figure 4-1, you should identify the specific RVSM Authorization Group for your
request. Include sufficient administrative information to allow the FAA inspector
to make the necessary form field entries when creating the authorization
document. For part 91 LOAs, samples of the needed administrative information is
located on the FAA Web site,
http://www.faa.gov/air_traffic/separation_standards/rvsm/documentation. Scroll
down to the Getting Started section and locate the appropriate document titled
Information Sheet for Part 91 RVSM Letter of Authorization (LOA). Use of the
information sheet will help you organize required information needed for
authorization. Providing sufficient information to the CHDO can assist in
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AC 91-85A
streamlining the application process and help prevent processing delays while the
inspector waits for the needed information to be submitted.
4.2.1
What are the General Steps an Applicant will take when its Application Falls Within
RVSM Authorization Group I, RVSM Authorization Amendments?
4.2.1.1
4.2.1.2
4.2.1.3
4.2.2
The authorization holder should also provide such further information as the
FSDO, CHDO, or IFO may request in order to efficiently process the request.
What are the General Steps an Applicant will take when its Application Falls Within
RVSM Authorization Group II, RVSM Authorization Based on One or More Existing
RVSM Authorization Elements?
4.2.2.1
4.2.2.2
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AC 91-85A
requirements (or to be able to gain such approvals) and any of the
other RVSM Authorization Elements listed in Chapter 3; and
4. Asks for the issuance of an RVSM authorization applying to the
operation of the aircraft by that proposed RVSM Operator.
4.2.2.3
4.2.3
4.2.4
Provide such further information as the FSDO, CHDO, or IFO may request in
order to efficiently process the request.
What are the General Steps an Applicant will take when its Application Falls Within
RVSM Authorization Group III, RVSM Authorization Not Based on One or More
Existing RVSM Authorization Elements?
4.2.3.1
In the event a proposed new or existing approved RVSM Operator seeks the
issuance of an RVSM authorization not based on any existing RVSM
Authorization Element, then neither Authorization Group I nor II above will
apply.
4.2.3.2
4.2.3.3
The applicant should also provide such further information as the FSDO,
CHDO, or IFO may request in order to efficiently process the request.
The RVSM Matrix. A detailed description of Figure 4-1 is provided in paragraph 2.4.
Figure 4-1. RVSM Decision Matrix
RVSM DECISION MATRIX
AUTHORIZATION GROUP I:
RVSM AUTHORIZATION AMENDMENTS
I.
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AC 91-85A
I.
I.
C. Applicable Procedures the Responsible FSDO, CHDO, or IFO Will Follow Upon a
Request for an Administrative Change to an Existing RVSM Authorization
1. Review the request and supporting documentation received from the RVSM authorization
holder to determine if it appears an amended RVSM authorization amendment is warranted.
2. Re-issue the amended RVSM authorization identical to the initial RVSM authorization in all
respects other than reflecting the new amended information; and
3. If the nature of the requested amendment is to change the primary business address from
one FSDO service area to another, see the additional applicable guidance in FAA
Order 8900.1, Volume 3, Chapter 2, Section 2, Responsibility of Part 91 Letters of
Authorization (LOA).
4. If an existing RVSM authorization holder has made a written affirmation none of the
underlying previously accepted RVSM Authorization Elements has changed or will change,
and there is no other information provided to the FSDO raising any questions or concerns
with respect to the on-going validity or applicability of those RVSM Authorization
Elements, then, subject to paragraph 2.4.4, the FSDO, CHDO, or IFO should issue the
requested amendment without further inspections being required.
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II.
II.
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II.
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What is the General Process the FAA will Follow Upon Submission of the Request
for an RVSM Authorization or Amended Authorization? Once application is made,
the FAA will begin the process of review and evaluation of the documentation submitted.
When the FAA determines the airworthiness and operational requirements of the
application are met, the FAA will proceed with issuing the authorization.
5.2
5.2.1
Parts 121, 125, and 135 Operators. Authorization for parts 121, 125, and 135 Operators to
operate in RVSM airspace should be granted through the issuance of an OpSpec
paragraph from Part B (En Route Authorizations, Limitations, and Procedures) and
Part D (Aircraft Authorization). Each aircraft for which the Operator is granted authority
should be listed in the OpSpecs. Authorization to conduct RVSM operations in an RVSM
area of operations new to the Operator should be granted by adding the Part B RVSM
OpSpecs paragraph number to the appropriate area of operations in the Part B paragraph:
Authorized Areas of En Route Operation Limitations and Procedures.
5.2.2
Part 129 Operators. The operational authorization of RVSM for part 129 is provided by
the State of the Operator. OpSpec A003 is used to confirm that the foreign air carrier has
operational approval. The State of the Operator must have regulation and supporting
guidance documents for the issuance of RVSM. The following are examples of guidance
documents the FAA considers to be consistent with ICAO standards on RVSM.
5.2.2.1
The current edition of this advisory circular (AC) (91 85, Authorization of
Aircraft and Operators for Flight in Reduces Vertical Separation Minimum
Airspace); and Joint Aviation Authority (JAA) Temporary Guidance TGL-6.
Note: For part 129 Operators, inspector guidance for paragraph A003
is contained in FAA Order 8900.1, Volume 12, Chapter 2, Section 3.
5.2.3
Part 91K Operators. Part 91K Operators authorization to operate in RVSM airspace
should be granted through the issuance of an MSpecs paragraph from Part B and Part D.
Each aircraft for which the Operator is granted authority should be listed in MSpecs.
Authorization to conduct RVSM operations in an RVSM area of operations new to the
Operator should be granted by adding the Part B RVSM MSpecs paragraph number to the
appropriate area of operations in the Part B paragraph.
5.2.4
Parts 91 and 125 (LODA Holder) Operators. Part 91 Operators and part 125 Operators
holding a LODA should be issued a LOA when the initial authorization process has been
completed.
Note: LODA is a formal authorization issued by the FAA CHDO, authorizing a
deviation from specified sections of part 125 and identified in WebOPSS
(125M database) as an A125 LODA operator.
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5.2.5
AC 91-85A
LOA Exemptions. Operators issued OpSpecs are not required to obtain an LOA for those
operations conducted under part 91 provided that:
1. The aircraft is operated under the Operator name listed on the OpSpecs.
2. The flight is conducted in an area of operations listed in the OpSpecs.
3. The aircraft is operated under the conditions under which the OpSpecs were
granted (e.g., if the Operator holds 121 or 135 OpSpecs, then the pilots used
for the part 91 operation must have received part 121 or 135 training.)
4. Each part 91 operation, not associated with a certificated operator, will need a
LOA to operate in RVSM airspace.
5.3
What are the Conditions That Would Require the Removal of an RVSM
Authorization?
Note: Examples of reasons for amendment, revocation, or restriction of RVSM
authorization include, but are not limited to, the reasons listed in part 91
appendix G, section 7.
5.3.1
5.3.2
Error Categories. Height-keeping errors fall into two broad categories: 1) errors caused
by malfunction of aircraft equipment, and 2) operational errors. An operator who
commits one or more error(s) of either variety may be required to forfeit authority for
RVSM operations. If a problem is identified related to one specific aircraft type, then
RVSM authority may be removed for the operator for that specific type.
5.3.3
Effective, Timely Response. The operator should make an effective, timely response to
each height-keeping error. The FAA may consider removing RVSM operational
authorization if the operator response to a height-keeping error is not effective or timely.
The FAA should also consider the operators past performance record in determining the
action to take. If an operator shows a history of operational and/or airworthiness errors,
then authorization may be removed until the root causes of these errors are shown to be
eliminated and RVSM programs and procedures are shown to be effective. The FAA will
review each situation on a case-by-case basis.
5.3.4
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AC 91-85A
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Appendix A
APPENDIX A. RVSM AIRWORTHINESS CERTIFICATION
CONTENTS
Paragraph
Page
A.1
A.2
A.3
A.4
A.5
A.6
A.7
A.8
A.9
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Appendix A
Introduction.
A.1.1 General. This Appendix provides guidance on the aircraft airworthiness certification
process for Reduced Vertical Separation Minimum (RVSM) compliance. Key elements
necessary to substantiate the aircraft systems performance required for RVSM
certification are summarized. Differences between a Group and Non-Group aircraft
certification program are presented. A comprehensive discussion of altimetry system
error (ASE) and ASE variation is also provided.
Note: For additional information on obtaining RVSM airworthiness certification
contact the appropriate FAA Field Office serving your geographic area for
guidance. Contact information for Aircraft Certification Offices (ACO) can be
found on the FAA Web site at www.faa.gov.
A.1.2 Definitions.
1. Aircraft Group. A group of aircraft of nominally identical design and build
with respect to all details that could influence the accuracy of height-keeping
performance.
2. Air Data Sensor. Line replaceable units designed to detect air data
characteristics (e.g., pressure, temperature, etc.) to support the air data system
of the aircraft.
3. Air Data System. Systems used to collect and process air data characteristics
from various sensors to compute critical air data parameters (e.g., altitude,
airspeed, height deviation, and temperature) for use by the pilot and other
systems in the aircraft.
4. Altimetry System Error (ASE). The difference between the pressure altitude
displayed to the flightcrew when referenced to International System of Units
(SI) standard ground pressure setting (29.92 in. Hg/1013.25 hPa) and free
stream pressure altitude.
5. Assigned Altitude Deviation (AAD). The difference between the altitude
transmitted by a Mode C transponder and the assigned altitude/flight level
(FL).
6. Automatic Altitude Control System. Any system designed to automatically
control the aircraft to a referenced pressure altitude.
7. Avionics Error. The error in the processes of converting the sensed pressure
into an electrical output, of applying any static source error correction (SSEC)
as appropriate, and of displaying the corresponding altitude.
8. Basic RVSM Envelope. The range of Mach numbers and gross weights within
the altitude ranges FL 290 to FL 410 (or max available altitude) where an
aircraft is expected to operate most frequently.
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Appendix A
9. Derivative Aircraft. Aircraft of the same model type, certified under the same
type certificate (TC). The aircraft may have different exterior dimensions,
such as fuselage length and wing span, but share the same altimetry system
architecture. In addition, derivative aircraft share the same SSEC at RVSM
flight levels. In most cases, derivative aircraft will have differing flight
envelopes, so the RVSM flight envelope defined for the Group must be
carefully constructed such that the performance of all models within the
Group is captured.
10. Full RVSM Envelope. The entire range of operational Mach numbers, W/,
and altitude values over which the aircraft is operated within RVSM airspace.
11. Height-Keeping Capability. Aircraft height-keeping performance expected
under nominal environmental operating conditions with proper aircraft
operating practices and maintenance.
12. Height-Keeping Performance. The observed performance of an aircraft with
respect to adherence to a flight level.
13. Instruction for Continued Airworthiness (ICA). Documentation giving
instructions and requirements for the maintenance essential to the continued
airworthiness of an aircraft.
14. Non-Group Aircraft. An aircraft for which the operator applies for approval
on the characteristics of the unique airframe rather than on a group basis.
15. Residual Static Source Error (SSE). The amount by which SSE remains
undercorrected or overcorrected after application of an SSEC.
16. Reduced Vertical Separation Minimum (RVSM). Designated airspace,
typically between FL 290 and FL 410, where 1000 vertical separation
between aircraft is applied. This airspace is considered special qualification
airspace.
17. Static Source Error (SSE). The difference between the pressure sensed by the
aircraft static source and the undisturbed ambient pressure.
18. Static Source Error Correction (SSEC). A correction applied to the altimetry
system to produce minimal residual SSE.
19. Total Vertical Error (TVE). Vertical geometric difference between the actual
pressure altitude flown by an aircraft and its assigned pressure altitude (FL).
20. Worst Case Avionics. The combination of tolerance values, specified by the
manufacturer for the altimetry fit into the aircraft, which gives the largest
combined absolute value of avionics errors.
21. W/. Aircraft weight, W, divided by the atmospheric pressure ratio, .
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Appendix A
A.1.3.2
It would be difficult to show all of the gross weight, altitude, and speed
conditions constituting the RVSM envelope(s) on a single plot. This is
because most of the speed boundaries of the envelopes are a function of both
altitude and gross weight. As a result, a separate chart of altitude vs. Mach
would be required for each aircraft gross weight. Aircraft performance
engineers commonly use the following technique to solve this problem.
A.1.3.3
For most aircraft with RVSM altitude capability, the required flight envelope
can be collapsed to a single chart, with good approximation, by use of the
parameter W/ (weight divided by atmospheric pressure ratio). This fact is
due to the relationship between W/ and the fundamental aerodynamic
variables M and lift coefficient as shown below.
W/ =1481.4 CL M2 SREF
where = ambient pressure at flight altitude
divided by sea level standard pressure
of 29.92126 inches Hg.
W/ = Weight over Atmospheric Pressure Ratio.
CL = Lift Coefficient (CL = L/qSREF).
L = Lift (in cruise flight L is equal to W).
q = Dynamic Pressure, q = 1481.4M2 .
Dynamic pressure is in the form of lbs/ft2.
M = Mach number.
SREF = Reference Wing Area in square feet.
W is the weight in pounds.
A.1.3.4
As a result, the flight envelope may be collapsed into one chart by simply
plotting W/, rather than altitude, versus Mach number. Since is a fixed
value for a given altitude, weight can be obtained for a given condition by
simply multiplying the W/ value by .
A.1.3.5
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A.2
AC 91-85A
Appendix A
A.2.1 General. For the purposes of RVSM approval, the aircraft flight envelope is considered in
two parts: 1) the full RVSM envelope, and 2) the basic RVSM envelope. The basic
RVSM envelope is the part of the flight envelope where aircraft operate the majority of
time. The full RVSM envelope is the entire range of operational Mach numbers, W/,
and altitude values over which the aircraft is operated within RVSM airspace. In general,
the full RVSM envelope comprises parts of the flight envelope where the aircraft
operates less frequently and where a larger ASE tolerance is allowed.
A.2.2 Full RVSM Envelope. The full RVSM envelope will comprise the entire range of
operational Mach number, W/, and altitude values over which the aircraft can operate
within RVSM airspace. Table A.2-1 establishes the parameters to consider.
Table A.2-1. Full RVSM Envelope Boundaries
Lower Boundary
is defined by:
Upper Boundary
is defined by:
Altitude
FL 290
Mach or Speed
Gross Weight
A.2.3 Basic RVSM Envelope. The boundaries for the basic RVSM envelope are the same as
those for the full RVSM envelope except in regard to the upper Mach boundary.
A.2.3.1
For the basic RVSM envelope, the upper Mach boundary may be limited to a
range of airspeeds over which the aircraft Group can reasonably expect to
operate most frequently. The manufacturer or design organization should
define this boundary for each aircraft Group. It may be defined as equal to the
upper Mach/airspeed boundary defined for the full RVSM envelope or a
specified lower value. This lower value should not be less than the Long
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Appendix A
Range Cruise Mach number plus .04 Mach unless limited by available cruise
thrust, buffet, or other aircraft flight limitations.
A.2.3.2
A.3
Long Range Cruise Mach number is the Mach for 99 percent of best fuel
mileage at the particular W/ under consideration.
A.3.1 Group Aircraft. Aircraft comprising a Group must be of nominally identical design and
build with respect to all details that could influence the accuracy of the height-keeping
performance. The following conditions should be met:
1. Aircraft should be approved by the same TC, TC amendment, or
Supplemental Type Certificate (STC), as applicable.
2. For derivative aircraft, it may be possible to use the database from the parent
configuration to minimize the amount of additional data required to show
compliance. The extent of additional data required will depend on the nature
of the changes between the parent aircraft and the derivative aircraft.
3. The static system of each aircraft should be installed in a nominally identical
manner and position. The same SSEC should be incorporated in all aircraft of
the Group.
4. The avionics units installed on each aircraft to meet the minimum RVSM
equipment requirements (paragraph A.4) should be manufactured to the
manufacturers same specification, and have the same equipment part number
and software part number (or version and revision).
Note: Aircraft which have avionic units which are of a different manufacturer or
equipment part number, software part number (or version and revision) may be
considered part of the Group if the applicant demonstrates to the appropriate FAA
office this standard of avionic equipment provides identical or better system
performance.
5. The airframe manufacturer or design organization produced or provided the
RVSM data package.
A.3.2 Non-Group Aircraft. If an airframe does not meet the conditions of paragraph A.3.1 to
qualify as a member of a Group or is presented as an individual airframe for approval,
then it must be considered as a Non-Group aircraft for the purposes of RVSM approval.
A.4
A.4.1 Equipment for RVSM Operations. The minimum equipment fit should be as presented
below. Additional examples of aircraft systems found on older, legacy airframes are
presented in paragraph A.6.
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A.4.1.1
AC 91-85A
Appendix A
Two Independent Altitude Measurement Systems. Each system should be
comprised and configured with the following elements:
A.4.1.1.1
A.4.1.1.2
A.4.1.1.3
A.4.1.1.4
A.4.1.1.5
A.4.1.1.6
A.4.1.1.7
Output to the Automatic Altitude Control and Altitude Alert Systems. The
altimetry system equipment fit should provide reference signals for
automatic altitude control and alerting at selected altitude. These signals
should be derived from an altitude measurement system meeting the full
requirements of Appendix A. The output may be used either directly or
combined with other sensor signals. If SSEC is necessary in order to satisfy
the requirements of paragraphs A.5.2.1 and A.5.2.2, or A.5.3.2, then an
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Appendix A
equivalent SSEC must be applied to the altitude control output. The output
may be an altitude deviation signal, relative to the selected altitude, or a
suitable absolute altitude output. Whatever the system architecture and
SSEC system, the difference between the output to the altitude control
system and the altitude displayed must be minimal.
A.4.1.1.8
A.4.1.1.9
Air Data Systems and Configurations with Multiple Static Source Inputs.
Many aircraft are produced with air data systems making use of three or
more static source inputs, and/or three or more air data computers (ADC).
Such systems (often referred to as triplex systems or voting schemes)
are designed with integrated algorithms that monitor and compare the
pressures sensed at the static sources. Sources providing good pressure
values are used in the calculation of corrected altitude. Such configurations
are acceptable provided at least two air data systems meet the requirements
of paragraphs A4.1.1.1 through A4.1.1.8. Upon failure of one air data
system, a second system must remain fully functional in compliance with
the requirements of paragraphs A4.1.1.1 through A4.1.1.8.
A.4.1.2
A.4.1.3
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Appendix A
1. The altitude deviation warning system should signal an alert when
the altitude displayed to the flightcrew deviates from selected
altitude by more than a nominal value.
A.4.1.4
A.4.1.4.1
A.4.1.4.2
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A.5
AC 91-85A
Appendix A
A.5.1 General. The statistical performance statements of ICAO Doc. 9574, Manual on the
Implementation of a 300 m (1,000 ft) Vertical Separation Minimum Between
FL 290-FL 410 Inclusive, for a population of aircraft (see Appendix D) are translated into
airworthiness standards by assessment of the characteristics of ASE and altitude control.
The following standards differ in some respects from that document, but they are
consistent with the requirements of RVSM and in accordance with 14 CFR part 91
appendix G, section 2.
A.5.2 Group Approval.
A.5.2.1
A.5.2.2
A.5.2.3
Aircraft types for which application for type certification or major change in
type design is made after April 9, 1997, should meet the criteria established
for the basic envelope in the full RVSM envelope. The FAA will consider
factors providing an equivalent level of safety in the application of this criteria
as stated in part 21, 21.21b(1).
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Appendix A
A.5.3.2
A.6
A.5.3.3
A.5.3.4
A.6.1 Background. This paragraph provides additional guidance regarding configurations found
on older model airplanes (also known as legacy airplanes, e.g., B707, DC-8, older
business jet, and turboprop aircraft, etc.) for which RVSM approval is sought.
A.6.2 Single Autopilot Installation. Paragraph A.4.1.1.7 states the air data system should
provide reference signals for automatic control and alerting at selected altitude. These
signals should preferably be derived from an altitude measurement system meeting the
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Appendix A
full requirements of this Appendix. In addition, paragraph A.4.1.1.7 states the altimetry
system must provide an output which can be used by an automatic altitude control system
to control the aircraft at a commanded altitude. The output may be used either directly or
combined with other sensor signals. The altitude control output may be an altitude
deviation signal, relative to the selected altitude, or a suitable absolute altitude output.
A.6.2.1
A distinction can be made between signals derived from an ADC and signals
derived from an altitude measurement system. Paragraph A.4.1.1.7 does not
mandate the need for dual ADC inputs to the automatic altitude control
system.
A.6.2.2
Several airplane model types are equipped with a single autopilot installation.
In many cases, the autopilot is only capable of receiving altitude hold inputs
from a single source. It has been further noted retrofitting of these autopilot
installations to receive altitude hold input from additional sources
(e.g., another ADC) may yield one or more of the following problems:
1. The retrofit costs are a significant percentage of the total worth of
the airframe.
2. The retrofit is not possible without replacement of the autopilot.
3. The retrofit increases air data system complexity, which in turn
increases the scenarios and rates of failure.
4. Upgraded avionics (i.e., ADCs) are not available, or the vendors
will not support retrofits.
A.6.2.3
There are two common avionics configurations that may meet RVSM
requirements, but do not have dual ADC input to the autopilot. A general
description and possible means of compliance are given below. They are:
1. Figure A.6-1, Example of Air Data System/Autopilot
Configuration.
2. Figure A.6-2, Single Air Data Computer Configuration for
Autopilot Input.
A.6.2.4
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Appendix A
Figure A.6-1. Example of Air Data System/Autopilot Configuration
autopilot
ADS
Cross-coupled
static sources
Alt
Cross-coupled
static sources
ADC 2
ADC 1
1800
1800
Alt
A.6.2.5
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Appendix A
Figure A.6-2. Single Air Data Computer Configuration for Autopilot Input
autopilot
Cross-coupled
static sources
ADC 1
Alt 1
Cross-coupled
static sources
ADC 2
1800
1800
Alt 2
The altitude alerter should function if either air data system or ADC
fails. If the altitude alert function is not operational, altitude hold
performance must be monitored manually.
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Appendix A
1. Precision tracking radar in conjunction with pressure calibration of
the atmosphere at test altitude.
2. Trailing cone.
3. Pacer aircraft. The pacer aircraft must have been directly calibrated
to a known standard. It is not acceptable to calibrate a pacer
aircraft by another pacer aircraft.
4. Any other method acceptable to the FAA or approving authority.
Note: Data acquired using elements from the RVSM monitoring
program, such as a ground-based height monitoring unit (HMU) or
Aircraft Geometric Height Measurement Element (AGHME), or a
portable Global Positioning System (GPS)-based monitoring unit
(GMU), is not acceptable for substantiating the ASE performance
specified in paragraphs A.5.2 and A.5.3.
A.7.1.2
ASE will generally vary with flight condition. The data package should
provide coverage of the RVSM envelope sufficient to define the largest errors
in the basic and full RVSM envelopes. Note in the case of Group approval the
worst flight condition may be different for each of the requirements of
paragraphs A.5.2.1 and A.5.2.2, and each should be evaluated. Similarly, for
Non-Group approval, the worst flight condition may be different for each of
the requirements of paragraph A.5.3.2 and each should be evaluated.
A.7.2.1.1
A.7.2.1.2
A.7.2.1.3
A.7.2.1.4
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A.8
AC 91-85A
Appendix A
Airframe to airframe variability of SSE, including the following:
Static port variation (for aircraft configured with static sources flush to
the skin surface). Sources of variation include port step-height,
degradation, and static port condition.
A.7.2.2
A.7.2.3
This document does not specify separate limits for the various error sources
contributing to the mean and variable components of ASE as long as the
overall ASE accuracy requirements of paragraphs A.5.2 or A.5.3 are met. For
example, in the case of Group approval, the smaller the mean of the Group
and the more stringent the avionics standard, the larger the available
allowance for SSE variations. In all cases, present the trade-off adopted in the
data package in the form of an error budget including all significant error
sources.
A.8.1 General. The ASE budget demonstrates the allocation of tolerances among the various
parts of the altimetry system is, for the particular data package, consistent with the overall
statistical ASE requirements. These individual tolerances within the ASE budget
represent the maximum error levels for each of the air data system components
contributing to ASE. These error levels form the basis of the maintenance procedures
used to substantiate the RVSM airworthiness compliance status of Group or Non-Group
aircraft. The component error evaluation should be assessed at the worst flight condition
in the basic and full envelope.
A.8.2 Altimetry System Error (ASE) Components.
A.8.2.1
General. Figure A.8-1, Altimetry System Error and its Components, shows
the breakdown of total ASE into its main components, with each error block
representing the error associated with one of the functions needed to generate
a display of pressure altitude. This breakdown encompasses all ASEs that can
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Appendix A
occur, although different system architectures may combine the components
in slightly different ways.
A.8.2.1.1
A.8.2.1.2
SSE is the difference between the undisturbed ambient pressure and the
pressure within the static port at the input end of the static pressure line.
A.8.2.1.3
Static Line Error is any difference in pressure along the length of the line.
A.8.2.1.4
A.8.2.1.5
Perfect SSEC would be that correction which compensated exactly for the
SSE actually present at any time. If such a correction could be applied, then
the resulting value of Hp calculated by the system would differ from the
actual altitude only by the static line error plus the pressure measurement
and conversion error. In general, this cannot be achieved, so although the
Actual SSEC can be expected to reduce the effect of SSE, it will do so
imperfectly.
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Appendix A
Figure A.8-1. Altimetry System Error and Its Components
A.8.2.1.6
A.8.2.1.7
Between Hp and displayed altitude occur the baro-correction error and the
display error. Figure A.8-1 represents their sequence for a self-sensing
altimeter system. ADC systems can implement baro-correction in a number
of ways that would modify slightly this part of the block diagram, but the
errors would still be associated with either the baro-correction function or
the display function. The only exception is those systems that can be
switched to operate the display directly from the Hp signal. These systems
can eliminate baro-correction error where standard ground pressure setting
is used, as in RVSM operations.
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Appendix A
A.8.2.2
SSE Components. The component parts of SSE are presented in Table A.8-2,
with the factors controlling their magnitude.
A.8.2.2.1
The reference SSE is the best estimate of actual SSE, for a single aircraft or
an aircraft Group, obtained from flight calibration measurements. It is
variable with operating condition, characteristically reducing to a family of
W/ curves that are functions of Mach. It includes the effect of any
aerodynamic compensation incorporated in the design, and once it has been
determined, the reference SSE is fixed for the single aircraft or Group,
although it may be revised if substantiated with subsequent data.
A.8.2.2.2
The test techniques used to derive the reference SSE will have some
measurement uncertainty associated with them, even though known
instrumentation errors will normally be eliminated from the data. For
trailing-cone measurements, the uncertainty arises from limitations on
pressure measurement accuracy, calibration of the trailing-cone installation,
and variability in installations where more than one is used. Once the
reference SSE has been determined, the actual measurement error is fixed,
but as it is unknown, it can only be handled within the ASE budget as an
estimated uncertainty.
A.8.2.2.3
A.8.2.3
Residual SSE.
A.8.2.3.1
Figure A.8-1 presents the components and factors. Residual SSE consists of
those error components that make actual SSE different from the reference
value, components 2), 3), and 4) from Table A.8-2, plus the amount by
which the actual SSEC differs from the value that would correct the
reference value exactly, components 2a), 2b), and 2c) from Table A.8-3.
A.8.2.3.2
There will generally be a difference between the SSEC that would exactly
compensate the reference SSE, and the SSEC that the avionics is designed to
apply. This arises from practical avionics design limitations. The resulting
Table A.8-3 error component 2a) will therefore be fixed, for a particular
flight condition, for the single aircraft or Group. Additional variable
errors 2b) and 2c) arise from those factors causing a particular set of
avionics to apply an actual SSEC that differs from its design value.
A.8.2.3.3
The relationship between perfect SSEC, reference SSEC, design SSEC, and
actual SSEC is illustrated in Figure A.8-4, Static Source Error/Static Source
Error Correction Relationships for Altimetry System Error Where Static
Line, Pressure Measurement, and Conversion Errors Are Zero, for the case
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Appendix A
where static line errors and pressure measurements and conversion errors
are taken as zero.
A.8.2.3.4
Error Components
Airframe Effects
Operating Condition (M, Hp, , )*
Geometry:
Shape of airframe
Location of static sources
Variations of surface contour near the
sources
Variations in fit of nearby doors, skin
panels, or other items
Probe/Port Effects
Operating Condition (M, Hp, , )*
Geometry:
Shape of probe/port
Manufacturing variations
Installation variations
*M
Hp
Mach, speed;
pressure altitude;
angle of attack;
yaw (sideslip).
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Appendix A
Table A.8-3. Residual Static Source Error (Aircraft with Avionic Static Source Error
Correction)
(Cause: Difference Between the Static Source Error Correction Actually Applied and the
Actual Static Source Error)
Factors
Error Components
1) As for SSE.
PLUS
2) Source of input data for SSEC function.
a) Where SSEC is a function of Mach:
i) PS sensing: difference in SSEC from
reference SSE.
ii) PS measurement: pressure transduction
error.
iii) PT errors: mainly pressure transduction
error.
b) Where SSEC is a function of Angle of
Attack:
i) Geometric effects on alpha
Sensor tolerances
Installation tolerances
Local surface variations
ii) Measurement error
Angle transducer accuracy
3) Implementation of SSEC function.
a) Calculation of SSEC from input data.
b) Combination of SSEC with uncorrected
height.
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Appendix A
Figure A.8-4. Static Source Error/Static Source Error Correction Relationships for
Altimetry System Error Where Static Line, Pressure Measurement, and Conversion Errors
are Zero
Actual Altitude
Static Source Error Components
(2), (3) and (4) (see table A.8-2)
SSE
Residual Static
Source Error
(Total)
Perfect
SSEC
Reference
SSEC
Hp (Corrected)
Design
SSEC
Actual
SSEC
Hp (Uncorrected)
A.8.2.3.5
Static line errors arise from leaks and pneumatic lags. In level cruise, these
can be made negligible for a system correctly designed and correctly
installed.
A.8.2.3.6
Calibration uncertainty;
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Appendix A
2. The equipment specification usually covers the combined effect
of the error components. If the value of pressure measurements
and conversion error used in the error budget is the worst-case
specification value, then it is not necessary to assess the above
components separately. However, calibration uncertainty,
nominal design performance, and effect of operating
environment can all contribute to bias errors within the
equipment tolerance. Therefore, if it is desired to take statistical
account of the likely spread of errors within the tolerance band, it
will be necessary to assess their likely interaction for the
particular hardware design under consideration.
3. It is particularly important to ensure the specified environmental
performance is adequate for the intended application.
A.8.2.3.7
A.8.3 ASE Component Error Budget: Group Approval. Where approval is sought for an aircraft
Group, the data package must be sufficient to show the requirements of paragraphs A.5.1
and A.5.2 are met. Because of the statistical nature of these requirements, the content of
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Appendix A
the data package may vary considerably from Group to Group. Paragraph A.8 should
serve as a guide to properly account for ASE sources.
A.8.3.1
A.8.3.2
A.8.3.3
A.8.3.4
In many cases, one or more of the major ASE sources will be aerodynamic in
nature (such as variations in the aircraft surface contour near the static
pressure source). If evaluation of these errors is based on geometric
measurements, substantiation should be provided that the methodology used is
adequate to ensure compliance. (See paragraph A.9, Figure A.9-2,
Compliance Demonstration Ground-To-Flight Test Correlation Process
Example.)
A.8.3.5
A.8.3.6
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Appendix A
D.1.5.3 required reassessment. This item states, Each individual aircraft in
the Group must be built to have ASE contained within 200 ft. This
statement does not mean every airframe should be calibrated with a trailing
cone or equivalent to demonstrate ASE is within 200 ft. Such an interpretation
would be unduly onerous considering the risk analysis allows for a small
proportion of aircraft to exceed 200 ft. However, if any aircraft is identified as
having an error exceeding 200 ft then it should receive corrective action.
A.8.4 ASE Component Error Budget: Non-Group Approval. Where an aircraft is submitted for
approval as a Non-Group aircraft, the data should be sufficient to show the requirements
of paragraph A.5.3.2 are met. The data package should specify how the ASE budget has
been allocated between residual SSE and avionics error. The operator and the FAA
should agree on what data will satisfy approval requirements. The following data should
be acquired and presented:
1. Calibration of the avionics used in the flight test as required establishing
actual avionics errors contributing to ASE. Since the purpose of the flight test
is to determine the residual SSE, specially calibrated altimetry equipment may
be used.
2. All avionics equipment contributing to ASE must be identified by function
and part number. The applicant must demonstrate the avionics equipment can
meet the requirements established according to the error budget when
operating the equipment in the environmental conditions expected during
RVSM operations.
3. Specifications for the installed altimetry avionics equipment indicating the
largest allowable errors must be presented. The error sources shown in
paragraph A.7.2.1.1 through A.7.2.1.5 are necessary elements of the altimetry
system component error budget for a Non-Group aircraft.
A.9
A.9.1 General. Paragraph A.8.3.4 requires the methodology used to establish the SSE be
substantiated. Further, maintenance procedures must be established to ensure conformity
of both newly manufactured airplanes, and those with in-service history. There may be
many ways of satisfying these requirements; two examples are included below.
A.9.1.1
A.9.1.1.1
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Appendix A
aircraft will be flight test calibrated, where N and M are determined by the
manufacturer and agreed to by the approving authority. The data generated
by N inspections and M flight calibrations must be used to track the mean
and 3 SD values to ensure continued compliance of the model with the
requirements of paragraphs A.5.2.1 and A.5.2.2. As additional data are
acquired, they should be reviewed to determine if it is appropriate to change
the values of N and M as indicated by the quality of the results obtained.
A.9.1.1.2
There are various ways in which the flight test and inspection data might be
used to establish the correlation. The example shown in Figure A.9-2 is a
process in which each of the error sources for several airplanes is evaluated
based on bench tests, inspections, and analysis. Correlation between these
evaluations and the actual flight test results would be used to substantiate
the method. A highly favorable correlation may be used to augment flight
test data, and if appropriate, mitigate the need to conduct periodic flight tests
(every Mth aircraft) as presented in paragraph A.9.1.1.1 above.
A.9.1.1.3
The method illustrated in Figures A.9-1 and A.9-2 is appropriate for new
models since it does not rely on any preexisting database for the Group.
A.9.1.2
Example 2. Group Aircraft. Figure A.9-3, Process for Showing Initial and
Continued Compliance of Airframe Static Pressure Systems for In-Service
and New Model Aircraft, illustrates flight test calibrations should be
performed on a given number of aircraft and consistency rules for air data
information between all concerned systems verified. Geometric tolerances and
SSEC should be established to satisfy the requirements. A correlation should
be established between the design tolerances and the consistency rules. For
aircraft being manufactured, air data information for all aircraft should be
checked in terms of consistency in cruise conditions and every Mth aircraft
should be calibrated, where M is determined by the manufacturer and agreed
to by the approving authority. The data generated by the M flight calibrations
should be used to track the mean and 3 SD values to ensure continued
compliance of the Group with the requirements of paragraphs A.5.2.1 and
A.5.2.2.
A.9.1.3
A-26
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AC 91-85A
Appendix A
Figure A.9-1. Process for Showing Initial and Continued Compliance of Airframe Static
Pressure System
A-27
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AC 91-85A
Appendix A
Figure A.9-3. Process for Showing Initial and Continued Compliance of Airframe Static
Pressure Systems for In-Service and New Model Aircraft
A-28
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A.10
AC 91-85A
Appendix A
Maintenance Requirements.
A.10.1 General. The data package must include a definition of the procedures, inspections/tests,
and limits used to ensure all aircraft approved against the data package conform to type
design. All future approvals, whether of new build or in-service aircraft, must also meet
the error budget allowances developed according to paragraph A.8. The tolerances will be
established by the data package and include a methodology allowing for tracking the
mean and SD for new build aircraft.
A.10.1.1
Define compliance requirements and test procedures for each potential source
of ASE. Ensure the error sources remain as allocated in the ASE budget.
Provide guidance for corrective action in the event of equipment, test, and/or
inspection failure. Typical RVSM-specific maintenance procedures include
the following:
1. Verification of avionics component part numbers.
2. Air Data System Ground Test. This is a direct assessment of
altimetry system component errors and correct application of the
SSEC.
3. Assessment/measurement of the skin surrounding the static
sources. Skin waviness, skin splices/joints, access panels, radome
fit/fair, and damage.
4. Inspection of the pitot-static probe or static port. Erosion,
corrosion, damage, static port orifice degradation, static port
step-height, excessive or non-homogenous paint.
5. SmartProbe. Inspection for corrosion, erosion, damage,
degradation.
A.10.1.2
A.10.1.3
A.10.1.4
A-29
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AC 91-85A
Appendix A
1. Air Data System Modifications. Changes to the components
comprising an RVSM-compliant air data system cannot be
effectively evaluated without the development of a revised ASE
budget. Such modifications must be approved by the airframe
manufacturer or approved design organization.
2. Automatic Altitude Control and Altitude Alert System
Modifications. Changes to components comprising an
RVSM-compliant automatic altitude control or altitude alert
system should be evaluated by the airframe manufacturer or
approved design organization.
3. Altitude Reporting. As stated in paragraph A.4.1.2, any
transponder meeting or exceeding the requirements of Technical
Standard Order (TSO) C74( ), TSO C112( ), as applicable, in
accordance with the operational regulations under which the
airplane is approved.
4. Airframe Modifications. Over time, a RVSM-approved aircraft
may become a candidate for airframe modifications, such as
installation of large antennas, radomes, fairings, equipment
lockers, winglets, etc. Any modification changing the exterior
contour of the aircraft, or potentially impacting the air data system
static sources and or pneumatic configuration, aircraft weight,
and/or performance in any manner, must be evaluated by the
manufacturer or design organization to ascertain the RVSM
compliance status.
A.10.2.2
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AC 91-85A
Appendix A
2. An airplane flight manual supplement (AFMS). The AFMS should
summarize any RVSM-specific performance, configuration, and/or
operational considerations (paragraph A.10.1.3) specific to RVSM
performance.
A.11
A.10.2.3
The data package should include the required periodicity of the maintenance
procedures presented in paragraph A.10.1.1 and A.10.1.2, to ensure continued
airworthiness compliance with RVSM requirements.
A.10.2.4
The data package should include descriptions of any special procedures not
covered in paragraph A.10.1, but may be needed to ensure continued
compliance with RVSM requirements.
A.10.2.5
A.11.1 General. Obtaining RVSM airworthiness approval is a two-step process. First, the
manufacturer or design organization develops the data package through which to seek
airworthiness approval and submits the package to the appropriate ACO for approval.
Once the ACO approves the data package, the operator applies the procedures defined in
the package to obtain authorization from the Flight Standards District Office
(FSDO)/certificate-holding district office (CHDO)/certificate management office
(CMO)/International Field Office (IFO) (as appropriate) to use its aircraft to conduct
flight in RVSM airspace. The initial airworthiness review process must consider
continued airworthiness requirements. This paragraph summarizes the requirements of
the RVSM airworthiness approval data package, and presents a means of compliance for
a Group or Non-Group aircraft. All aircraft must meet the equipment, configuration, and
performance requirements of paragraph A.4, and the altimetry system performance
requirements of paragraph A.5.
A.11.2 Contents of the Data Package.
A.11.2.1
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AC 91-85A
Appendix A
4. The engineering data and compliance procedures required to:
A.11.2.2
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AC 91-85A
Appendix B
Introduction. Items listed in this appendix should be standardized and incorporated into
training programs and operating practices and procedures. Certain items may already be
adequately standardized in existing operator programs and procedures. New technologies
may also eliminate the need for certain crew actions. If this is the case, then the intent of
this guidance can be considered to be met.
Note: This advisory circular (AC) was written for use by a wide variety of
operator types (e.g., 14 CFR part 91, 91K, 121, 125, 129, 135 operators) and
therefore, certain items are included for purposes of clarity and completeness.
B.2
Flight Planning. During flight planning, the flightcrew and dispatchers, if applicable,
should pay particular attention to conditions which may affect operation in Reduced
Vertical Separation Minimum (RVSM) airspace. These include, but may not be limited
to:
1. Verifying the aircraft is approved for RVSM operations.
2. Annotating the flight plan to be filed with the Air Traffic Service Provider to
show the aircraft and operator are authorized for RVSM operations. Block 10
(equipment) of the International Civil Aviation Organization (ICAO) flight
plan (FAA Form 7233-4) should be annotated with the letter W for filing in
RVSM airspace.
3. For exceptions to the use of FAA Form 7233-4, see chapter 5 of the latest
version of the FAA Aeronautical Information Manual (AIM) for the proper
flight codes.
Note: An aircraft or operator not authorized for RVSM operations or an
operator/aircraft without operable RVSM equipment is referred to as non-RVSM.
If either the operator or the aircraft or both have not received RVSM authorization
the operator or dispatcher will not file the RVSM equipment code in the flight
plan.
4. Reported and forecast weather conditions on the route of flight.
5. Minimum equipment requirements pertaining to height-keeping systems.
6. If required for the specific aircraft group, accounting for any aircraft operating
restrictions related to RVSM airworthiness approval. (See Appendix A,
paragraph A.10.1.3.)
B.3
B-1
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AC 91-85A
Appendix B
The aircraft altimeters should be set to the local altimeter atmospheric pressure at
nautical height (QNH) setting and should display a known elevation (e.g., field
elevation) within the limits specified in aircraft operating manuals. The difference
between the known elevation and the elevation displayed on the altimeters should
not exceed 75 ft.
The two primary altimeters should also agree within limits specified by the
aircraft operating manual/Airplane Flight Manual (AFM), as applicable. An
alternative procedure using atmospheric pressure at field elevation (QFE) may
also be used.
Procedures Before RVSM Airspace Entry. If any of the required equipment fails prior
to the aircraft entering RVSM airspace, the pilot should request a new clearance so as to
avoid flight in this airspace. The following equipment should be operating normally at
entry into RVSM airspace:
1. Two primary altitude measurement systems.
2. One automatic altitude-control system.
3. One altitude-alerting device.
Note: The operator should ascertain the requirement for an operational
transponder in each RVSM area where operations are intended.
B.5
In-Flight Procedures. Incorporate the following policies into flightcrew training and
procedures:
1. Flightcrews should comply with aircraft operating restrictions (if required for
the specific aircraft group) related to RVSM airworthiness approval. (See
paragraph A.10.1.3.)
2. Place emphasis on promptly setting the sub-scale on all primary and standby
altimeters to 29.92 in. Hg/1013.25 hPa when climbing through the transition
altitude and rechecking for proper altimeter setting when reaching the initial
cleared flight level (CFL).
3. In level cruise, it is essential the aircraft is flown at the CFL. This requires
particular care is taken to ensure air traffic control (ATC) clearances are fully
B-2
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AC 91-85A
Appendix B
understood and followed. Except in contingency or emergency situations, the
aircraft should not intentionally depart from CFL without a positive clearance
from ATC.
4. During cleared transition between flight levels, the aircraft should not be
allowed to overshoot or undershoot the cleared flight level by more than
150 ft (45 m).
Note: It is recommended the level off be accomplished using the altitude capture
feature of the automatic altitude-control system, if installed.
5. An automatic altitude-control system should be operative and engaged during
level cruise, except when circumstances such as the need to retrim the aircraft
or turbulence require disengagement. In any event, adherence to cruise
altitude should be done by reference to one of the two primary altimeters.
6. The altitude-alerting system should be operational.
7. At cruise flight level the two primary altimeters should agree within 200 ft
(60 m) or a lesser value if specified in the aircraft operating manual. (Failure
to meet this condition will require that the altimetry system be reported as
defective and notified to ATC.) Note the difference between the primary and
stand by altimeters for use in contingency situations.
8. At intervals of approximately 1 hour, make cross-checks between the primary
altimeters and the stand-by altimeter.
The normal pilot scan of flight deck instruments should suffice for altimeter
crosschecking on most flights.
Some aircraft have automatic comparators that compare the two primary altimetry
systems. The comparators include a monitoring, warning, and fault function. The
faults may be recorded automatically by the system but a record of the differences
in the primary altimetry systems may not be easily derived.
Note: In oceanic and remote continental (procedural) airspace, even if the aircraft
is equipped with automatic comparators, the crew should be recording the
altimeter cross-checks for use in a contingency situation.
9. Normally, the altimetry system being used to control the aircraft should be
selected to provide the input to the altitude-reporting transponder transmitting
information to ATC.
B-3
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AC 91-85A
Appendix B
10. If ATC notifies the pilot of an assigned altitude deviation (AAD) error equal
to or exceeding 300 ft (90 m) then the pilot should take action to return to
cleared flight level (CFL) as quickly as possible.
11. Contingency procedures after entering RVSM airspace. The flight crew after
realizing that they no longer can comply with RVSM requirements (aircraft
system failure, weather, lost com, etc.) must request a new clearance from the
controller/radio operator as soon as the situation allows. If a new clearance is
not available or the nature of the emergency requires rapid action the pilot
should notify ATC of their action and contingency procedures. Operators
should refer to the RVSM section of the AIM when experiencing abnormal
situations and implementing contingency procedures. It is also the
responsibility of the crew to notify ATC when the implementation of the
contingency procedures is no longer required.
B.6
B.7
Special Emphasis Items: Flightcrew Training. The following items should also be
included in flightcrew training programs:
1. Operators are responsible for knowing the RVSM procedures in the areas of
intended operation. Operators starting RVSM operation in an RVSM area of
operation new to them should ensure their RVSM programs incorporate
RVSM policy and procedures unique to the new area of operations.
Note: Additional specific information on RVSM operational policy and
procedures in the domestic U.S., Alaska, Offshore Airspace, and the San Juan
flight information region (FIR) can be found in the AIM, Chapter 4, Section 6.
2. Importance of crewmembers cross-checking each other to ensure ATC
clearances are promptly and correctly complied with.
B-4
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AC 91-85A
Appendix B
B-5
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AC 91-85A
Appendix C
C-1
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AC 91-85A
Appendix C
C.1.3 Guidance To The Pilot In The Event Of Equipment Failures Or Encounters With
Turbulence After Entry Into RVSM Airspace (Including Expected ATC Actions).
C.1.3.1
The following material is provided with the purpose of giving the pilot
guidance on actions to take under certain conditions of equipment failure and
encounters with turbulence. It also describes the expected ATC controller
actions in these situations. It is recognized the pilot and controller will use
judgment to determine the action most appropriate to any given situation. The
guidance material recognizes for certain equipment failures, the safest course
of action may be for the aircraft to maintain the assigned flight level (FL) and
route while the pilot and controller take precautionary action to protect
separation. For extreme cases of equipment failure, however, the guidance
recognizes the safest course of action may be for the aircraft to depart from
the cleared FL or route by obtaining a revised ATC clearance; or if unable to
obtain prior ATC clearance, executing the established ICAO Doc. 4444 and
Doc. 7030 contingency maneuvers for the area of operation.
The pilot is: 1) unsure of the vertical position of the aircraft due to the loss or degradation of all
primary altimetry systems; or 2) unsure of the capability to maintain cleared flight level (CFL)
due to turbulence or loss of all automatic altitude control systems.
The pilot should:
C-2
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AC 91-85A
Appendix C
C-3
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AC 91-85A
Appendix C
Figure C.1-3. Expanded Scenario 1
All automatic altitude control systems fail (e.g., Automatic Altitude Hold).
C-4
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AC 91-85A
Appendix C
Figure C.1-4. Expanded Scenario 2
Loss of redundancy in primary altimetry systems.
C-5
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AC 91-85A
Appendix C
Figure C.1-6. Expanded Scenario 4
The primary altimeters diverge by more than 200 ft (60 m).
C-6
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Appendix C
C-7
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AC 91-85A
Appendix D
APPENDIX D. REVIEW OF ICAO DOCUMENT 9574
D.1
D.1.1 International Civil Aviation Organization (ICAO) Doc. 9574, Manual on the
Implementation of a 300 m (1,000 ft) Vertical Separation Minimum Between
FL 290-FL 410 Inclusive, covers the overall analysis of factors for achieving an
acceptable level of safety in a given airspace system. The major factors are passing
frequency, lateral navigation accuracy, and vertical overlap probability. Vertical overlap
probability is a consequence of errors in adhering accurately to assigned flight level (FL),
and this is the only factor addressed in the present document.
D.1.2 In ICAO Doc. 9574, Section 2.3.1 restated the vertical overlap probability requirement as
the aggregate of height-keeping errors of individual aircraft, which must lie within the
TVE distribution expressed as the simultaneous satisfaction of the following four
requirements:
D.1.2.1
D.1.2.2
D.1.2.3
D.1.2.4
D.1.3 The following characteristics presented in ICAO Doc. 9574 were developed to satisfy the
distributional limits in paragraph D.1.2.1, and to result in aircraft airworthiness having
negligible effect on meeting the requirements in paragraphs D.1.2.2, D.1.2.3, and D.1.2.4.
They are applicable statistically to individual groups of nominally identical aircraft
operating in the airspace. These characteristics describe the performance the groups need
to be capable of achieving in service, exclusive of human factors errors and extreme
environmental influences, if the airspace system Total Vertical Error (TVE) requirements
are to be satisfied. The following characteristics are the basis for development of this
document:
D.1.3.1
The mean altimetry system error (ASE) of the group must not exceed 80 ft
(25 m);
D.1.3.2
The sum of the absolute value of the ASEmean for the group and ASE3 SD
within the group must not exceed 245 ft (75 m); and
D.1.3.3
D-1
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AC 91-85A
Appendix D
frequency should decrease with increasing error magnitude at a rate that is at
least exponential.
D.1.4 ICAO Doc. 9574 recognized specialist study groups would develop the detailed
specifications to ensure the TVE objectives can be met over the full operational envelope
in Reduced Vertical Separation Minimum (RVSM) airspace for each aircraft group. In
determining the breakdown of tolerances between the elements of the system, it was
considered necessary to set system tolerances at levels recognizing the overall objectives
must be met operationally by aircraft and equipment subject to normal production
variability, including the airframe SSE, and normal in-service degradation. It was also
recognized that it would be necessary to develop specifications and procedures covering
the means for ensuring in-service degradation is controlled at an acceptable level.
D.1.5 Based on studies reported in ICAO Doc. 9536, Review of the General Concept of
Separation Panel (RGCSP), Volume 2, ICAO Doc. 9574 recommended the required
margin between operational performance and design capability should be achieved by
ensuring the performance requirements are developed to fulfill the following
requirements, where the narrower tolerance in paragraph D.1.5.2 is specifically intended
to allow for some degradation with increasing age:
D.1.5.1
The mean uncorrected residual position error static source error (SSE) of the
group will not exceed 80 ft (25 m);
D.1.5.2
The sum of the absolute value of the ASEmean for the group and ASE3 SD
within the group will not exceed 200 ft (60 m);
D.1.5.3
Each individual aircraft in the group will be built to have ASE contained
within 200 ft (60 m); and
D.1.5.4
D.1.6 These standards provide the basis for the separate performance aspects of airframe,
altimetry, altimetry equipment, and automatic altitude control system. It is important to
recognize the limits are based on studies (ICAO Doc. 9536, Volume 2) which showed
ASE tends to follow a normal distribution about a characteristic mean value for the
aircraft group. Therefore, the document should provide controls precluding the possibility
individual aircraft approvals could create clusters operating with a mean significantly
beyond 80 ft (25 m) in magnitude, such as could arise where elements of the altimetry
system generate bias errors additional to the mean corrected SSE.
D-2
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AC 91-85A
Appendix E
APPENDIX E. RVSM AUTHORIZATION OVERVIEW
E.1
E-1
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