The following text is taken from the presentation and speaker notes in
Managing Threats and Errors During Approach and Landing.
Note that the friction reports are relative to the wet stopping performance. Slide 27 shows this diagrammatically i.e. the reports don’t commence until the friction has already decreased to the wet value. Thus good on a wet runway is not ‘good’ when compared with dry performance and the certificated distances unless a max energy stop is performed.
The ICAO ‘ATC’ runway friction report codes relate to the surface conditions i.e ‘good’ on a wet runway relates wet stopping performance which is already degraded with respect to dry runway operations.
NORMAL - Maximum energy stops possible with little deterioration in certified
(dry) stopping distance.
GOOD - More braking is available than will be used in an average airline type deceleration. If a maximum energy stop were attempted
(wet),
some distance in excess of certified stopping distance would be expected.
FAIR - Sufficient braking and cornering force is available for a well-flown approach and landing using light braking. However,
excess speed or long touchdown would result in an extremely low safety factor depending on runway length and crosswind component. Careful planning and good judgment are required.
POOR - Very careful planning, judgment, and execution are absolutely essential.
Crosswind becomes a "priority one" consideration. While a safe and successful approach, landing, and stop can be accomplished if all factors are favorable, there is little room for error. [/b] Care must be exercised in every aspect of the operation and a very careful evaluation of all conditions is necessary.
Note: "Unreliable" will be reported when surface conditions do not permit a meaningful action value to be determined (i.e., standing water, slush, wet snow
[potential hydroplaning]).
“If the surface is affected by snow or ice and the braking action is reported as “good”, pilots should not expect to find conditions as good as on clean dry runway (where the available friction may well be greater than that needed in any case). The value “good” is a comparative value and is intended to mean that aeroplanes should not experience directional control or braking difficulties, especially when landing.” JAA WP061
Refs: (Most can be found via Google)
FAA NASA B 737 Aircraft test results from 1996 joint winter runway friction measurement program. T Yeager, NASA Langley
DoT Canada Procedures for Accounting for Runway Friction on Landing TC 14082E
DoT Canada Falcon 20 Aircraft Braking Performance on Wet Concrete Runway Surfaces No. TP 14273E
Re questions:
Are these definitions still valid? Yes
Are there other definitions for GOOD - FAIR - POOR - NIL in operational use?
Unfortunately yes, but these are unofficial, non ICAO standard, and only add confusion. Either non conforming ATC or both ATC and pilots make up their own interpretations of the definitions in an attempt to help others. Thus, the friction reports are also relative to the reporter’s aircraft type, his/her interpretation and the variability in the measuring device which can be significant.