Runway Condition Assessment Matrix - RCAM[PDF]

Introduction

Following several runway excursions leading to fatal accidents in the last few years, a workgroup from the FAA has been formed in order to determine a course of action in the prevention of runway overrun and excursions, one of the main causes of fatal injuries in aviation accidents nowadays.

One critical parameter amongst many is the determination of the runway state and its contamination when computing landing performance.
A matrix has been created to correlate the runway contamination versus the expected braking action.

See below the dramatic runway overrun of flight SWA1248 at Chicago Midway Airport in 2005:

Southwest Airlines Flight 1248 -1
One root cause of the incident was the non-correlation between the braking action selected in the in-flight performance computer and the actual contamination state of the runway.


Definitions used by the matrix

Contaminated

A runway is contaminated when more than 25 per cent of the runway surface area (whether in isolated areas or not) within the required length and width being used is covered by one of the following deposit:
  • standing water more than 3 mm deep;
  • slush more than 3 mm deep;
  • loose snow more than 20 mm deep;
  • compacted snow or ice, including wet ice.

Given the preceding definition, a wet runway is not a contaminated runway.

Considering the scope of the RCAM, these definitions are not applicable to other airport surfaces such as taxiways or aprons.

Contaminants

The matrix deals with the following contaminants:
  • Frost
  • Slush
  • Snow (dry, compacted, wet)
  • Water (standing water, slippery wet)
  • Ice

If a specific contaminant is not listed previously, there is no possible correlation between the expected and the actual braking actions.
Most of the time, operators will prohibit operations on such runways.

Refer to our article dealing with meteorological contaminants for complete definitions of every contaminant.

ICAO Matrix

Find below the ICAO Runway Condition Assessment Matrix (RCAM) sorted by Runway Condition Code (RCC).

This table is only applicable for landing.
The determination of takeoff performances, specifically of the acceleration-stop performance, lies on a different computation which requires the selection of the contaminant.
RCC Runway surface description Aeroplane control observation Braking action
6 Dry N/A N/A
5 Damp
Wet (less than 3 mm of water)
Frost

Less than 3 mm depth of:
Slush
Dry snow
Wet snow
Braking deceleration is normal for the wheel braking effort applied
AND
Directional control is normal.
GOOD
4 -15°C and colder Outside Air Temperature:
Compacted snow
Braking deceleration is not as good as expected for the wheel braking effort applied.
OR
Directional control is not as good as expected.
GOOD TO MEDIUM
3 Slippery when wet
Dry snow or wet snow over compacted snow

Greater than 3 mm depth of:
Dry snow
Wet snow

Warmer than -15°C Outside Air Temperature:
Compacted snow
Braking deceleration is noticeably reduced for the wheel braking effort applied.
OR
Directional control is noticeably reduced.
MEDIUM
2 Greater than 3 mm depth of:
Water
Slush
Braking deceleration is reduced for the wheel braking effort applied.
OR
Directional control is reduced.
MEDIUM TO POOR
1 Ice Braking deceleration is significantly reduced for the wheel braking effort applied.
OR
Directional control is significantly reduced.
POOR
0 Wet ice
Slush over ice
Water over compacted snow
Dry snow or wet snow over ice
Braking deceleration is minimal to non-existent for the wheel braking effort applied.
OR
Directional control is uncertain.
LESS THAN POOR / NIL


Be wary: the "OR" condition is not exclusive. Only one aspect is sufficient to qualify for adverse runway condition description.
The airport charts and NOTAMs contain the information in regard to slippery-wet runways (runway is slippery when wet).
Your aircraft-specific or your airline operating manual may include more operating restrictions and limitations than the ICAO Matrix.
For example, most operators and aircraft manufacturers will forbid runway operations when runway is considered runway condition code 0.

The term "FAIR" is not existing anymore in regard to braking action.
It has been replaced by the term "MEDIUM".

Recommendation to flight crew

Mu Friction Coefficient

For a while, airport operators were providing runway state by measuring the Mu Friction Coefficient.

Several studies have proven that there is no correlation between the friction coefficient and the actual braking action.

In most cases, this friction coefficient underestimates the actual adverse consequences of the runway contamination. The sensors used such as vehicle braking were not reliable.

Operators and aircraft manufacturers are encouraged by the ICAO to provide flight crews with operating limitations based on the RCAM. Flight crews are encouraged to disregard any friction coefficient and the use of the RCAM is therefore promoted as a flight safety item.

Partial contamination

The runway contamination information should be communicated either by NOTAMs or SNOWTAMs using thirds of the runway length.

Each third is dealt with independently (touchdown, midpoint, roll-out).

See also

Reference

Author

  • VID 200696 - Creation

DATE OF SUBMISSION

  • 14:47, 25 April 2020

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.