Landing distances and crosswind limitations (if applicable) contained in the aircraft flight manual (AFM) are demonstrated in accordance with specified performance criteria on runways that are bare, dry, and that have high surface friction characteristics. Unless some factor has been applied, these distances are only valid under similar runway conditions. Whenever a contaminant – such as water, snow or ice – is introduced to the runway surface, the effective coefficient of friction between the aircraft tire and runway is substantially reduced. The landing distance will increase and a crosswind may present directional control difficulties.
The average of the runway friction as measured by a decelerometer on runways with freezing or frozen contaminants is defined as the Canadian Runway Friction Index (CRFI). The decelerometer is an instrument mounted in a test vehicle that measures the decelerating forces acting on the vehicle when the brakes are applied. The instrument is graduated in increments from 0 to 1, the highest number being equivalent to the theoretical maximum decelerating capability of the vehicle on a dry surface. Small numbers represent low braking coefficients of friction while numbers on the order of 0.8 and above indicate the braking coefficients to be expected on bare and dry runways.
(B1667/20 NOTAMN
A) CAAA B) YY11141505 C) YY11142305
E) RSC 07 5/3/3 50 PCT 1/8IN DRY SNOW AND 25 PCT COMPACTED SNOW, 50 PCT COMPACTED SNOW AND 50 PCT 1/4IN DRY SNOW, 25 PCT COMPACTED SNOW AND 25 PCT 1/4IN DRY SNOW. 160FT WIDTH. 6IN SNOW DRIFTS 200FT FM THR 25. REMAINING WIDTH COMPACTED SNOW. VALID NOV 14 1457 – NOV 14 2257.
RSC 25 3/3/5 25 PCT COMPACTED SNOW AND 25 PCT 1/4IN DRY SNOW, 50 PCT COMPACTED SNOW AND 50 PCT 1/4IN DRY SNOW, 50 PCT 1/8IN DRY SNOW AND 25 PCT COMPACTED SNOW. 160FT WIDTH. 6IN SNOW DRIFTS 200FT FM THR 25. REMAINING WIDTH COMPACTED SNOW. VALID NOV 14 1457 – NOV 14 2257.
ADDN NON-GRF/TALPA INFO:
CRFI 07 -3C .40/.32/.30 OBS AT 2111141457.
CRFI 25 -3C .30/.32/.40 OBS AT 2111141457.
Reporting the runway surface condition information in thirds – with associated Runway Condition Codes (RWYCCs) – provides useful information for pilots. This format helps to improve pilot situational awareness by identifying where the contaminants that affect aeroplane performance and directional control are located on a runway.
The RWYCC is a number, from 0 to 6, which represents the slipperiness of a specific third of a runway, and provides a standardized “shorthand” for reporting this information. A RWYCC of 0 corresponds to an extremely slippery runway and 6 corresponds to a dry runway. RWYCCs also serve to enhance all pilots’ situational awareness of where the slipperiest runway conditions and contaminants are located on a runway. RWYCCs can be used by pilots to make a time of arrival landing performance assessment (for those aeroplanes with suitable performance information).
For example, in the report shown above (RSC 07 5/3/3) signifies that the first, second and final third of runway 07 have a RWYCC of 5, 3 and 3 respectively.
The chart below provides information for calculating headwind and crosswind components. It can be used to determine the minimum acceptable crosswind given a CRFI or vice versa
EXAMPLE
The wind is 40° off the runway heading at 20 knots. Find the intersection between the 20-knot arc and 40° line. The headwind is then read directly off the vertical axis and the CRFI is read directly off the horizontal axis. The headwind component is 15 knots and a crosswind component is 13 knots. The recommended minimum CRFI for a 13 knot crosswind component is 0.35. A takeoff or landing with a CRFI of 0.3 could result in uncontrollable drifting and yawing.