BACF Briefing

BRAKING ACTION COMPUTATION FUNCTION
NAVBLUE® RunwaySense Briefing
I. TODAY’S MEANS OF MEASURING RUNWAY SURFACE CONDITIONS
Today, there are typically three methods available by which runway surface
conditions are evaluated:
• Runway contaminant type and depth observations

• Ground surface friction measurements
• Braking action reports from pilots
Contaminant type and depth observations are in general physically conducted by

airport personnel on the runway surface. The conditions are assessed through a
combination of visual observations and spot-checks. However, it can be a difficult
task to consolidate what may be differing conditions across the entire width and
length of the runway into a succinct runway condition report.
In addition, during active precipitation and/or freezing/melting conditions, the

validity of the information may become outdated soon after it is issued.
Ground surface friction measurements provide a more quantitative approach to

taking measurements along certain points on a runway. However, as noted by the
NTSB, they are useful for identifying trends in runway surface condition but are
not recommended for use in predicting aircraft stopping performance. This is due
to the lack of correlation with aircraft braking performance, as well as variability
in equipment design and calibration.
While the airport operator is responsible for generating the Runway Condition
Codes for a runway, pilots are responsible for providing accurate braking action
reports. Indeed, providing braking action reports is a significant role that pilots
play in preventing runway excursions for all airplanes.
II. USING THE AIRCRAFT AS A SENSOR TO MEASURE RUNWAY CONDITION
1) Braking Action Computation Function
Airbus has developed a new aircraft function to address the need identified by
the NTSB and other national aviation Safety bodies, for “an operationally feasible
airplane-based braking ability / runway surface condition measurement and
communication system”. The implementation of this function on Airbus aircraft is
called the “Braking Action Computation Function’ (BACF)”.
AIR ARABIA 20.05.2023 1

The fundamental principle of the function is, post landing, to use the data
measured by the aircraft during its deceleration roll to identify the braking action
level. By using the aircraft performance model, it is possible to differentiate the
part of deceleration coming from either aerodynamic, thrust reverse, or wheel-
braking.
Subsequently, by comparing the actual wheel braking performance to models of

wheel-braking performance under different “reference” runway conditions, the
runway state which most closely resembles the experienced deceleration is
determined.
Additionally, using GPS data available from the aircraft navigation systems, it is
possible to identify which section of the runway the aircraft is on when a runway
state is identified. The function can identify several states at different points on
the runway.
A few seconds after the aircraft speed has decreased below 30kts, details about
the runway state become available to the pilot on a dedicated MCDU page
(fig.1). If the pilot felt that the runway was slippery, or in a different condition to
that communicated by Air Traffic Services (ATS), this information can be
accessed by the pilot and radioed to ATS at an appropriate moment.
(fig.1)
Example MCDU screen
with runway state
outputs from the BACF
2) RunwaySense by NAVBLUE
As shown in (fig.2), in addition to the information available to the pilot through

the MCDU, the data calculated by BACF is also sent automatically by ACARS
message to NAVBLUE.
AIR ARABIA 20.05.2023 2

NAVBLUE will collect and display the results on a web-service platform called
RunwaySense. The users of this service are expected to include airports, airline
operational centers, and air traffic control.
This technological approach is similar to the various mobile traffic applications

which share traffic data in real-time to allow drivers to see and avoid traffic jam.
The goal of this new Airbus-NAVBLUE technology is to provide a platform where

airspace users are sharing reports in real-time to better understand how the
runway condition is trending, and to allow the airport to anticipate and mitigate
slippery conditions. The more aircraft which participate in the sharing, the better
the real-time map of conditions becomes.
(fig.2) Integration of BACF & NAVBLUE’s RunwaySense® within airport and airline operations.
3) Airline Embodiment Status
The Airline has adopted and installed the BACF on the fleet. You will be enrolled in
a short and concise eLearning module on the Connect LMS to learn more about it.
The FCOM is being updated to include a description of this function in the

Systems Description section. Meanwhile, you may refer to NTP 06/23 for an
advance copy for your necessary information.
AIR ARABIA 20.05.2023 3

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BRAKING ACTION COMPUTATION FUNCTION

NAVBLUE® RunwaySense Briefing

I. TODAY’S MEANS OF MEASURING RUNWAY SURFACE CONDITIONS

• Runway contaminant type and depth observations

Contaminant type and depth observations are in general physically conducted by

In addition, during active precipitation and/or freezing/melting conditions, the

Ground surface friction measurements provide a more quantitative approach to

II. USING THE AIRCRAFT AS A SENSOR TO MEASURE RUNWAY CONDITION

1) Braking Action Computation Function

AIR ARABIA 20.05.2023 1

Subsequently, by comparing the actual wheel braking performance to models of

As shown in (fig.2), in addition to the information available to the pilot through

AIR ARABIA 20.05.2023 2

This technological approach is similar to the various mobile traffic applications

The goal of this new Airbus-NAVBLUE technology is to provide a platform where

3) Airline Embodiment Status

The FCOM is being updated to include a description of this function in the

AIR ARABIA 20.05.2023 3

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