¶ 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:
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 (GRF CONCEPT)
A runway is contaminated if more than 25 per cent of at least one third of the runway surface area (whether in isolated areas or not) within the required length and width being used is covered with more than 3mm of any contaminant.
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 (or Wet Ice)
- Water on top of compacted snow
- Dry snow or Wet snow on top of 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 (RWYCC).
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 (up to 3 mm of water) Frost Up to and including 3mm 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 OR Directional control is between Good and Medium. |
GOOD TO MEDIUM |
| 3 | Wet (slippery wet ICAO) Slippery Wet (EASA) Dry snow or wet snow over compacted snow (any depth) 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 OR Directional control is between Medium to Poor. |
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 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
ICAO has decided not to provide runway state by measuring the Mu (Friction Coefficient) values anymore, from the moment that GRF came into effect.
However, some airport operators (specially those still transitioning from the old format) may still use friction values in parallel with the new GRF concept (Global Reporting Format).
Important Note: 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.
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