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Braking Action & Runway Friction Reports & Advisories

Introduction:

  • Friction is defined as the ratio of the tangential force needed to maintain uniform relative motion between two contacting surfaces to the perpendicular force holding them in contact
    • Simply stated, friction quantifies slipperiness of pavement surfaces

Braking Action Reports and Advisories:

  • When available, ATC furnishes pilots the quality of braking action received from pilots or airport management
    • The quality of braking action is described by the terms "good," "good to medium," "medium," medium to poor", "poor," and "nil," or a combination of these terms
    • When pilots report the quality of braking action by using the terms noted above, they should use descriptive terms that are easily understood, such as, "braking action poor the first/last half of the runway," together with the particular type of aircraft
  • For Notice to Airmen (NOTAM) purposes, braking action reports are classified according to the most critical term ("good," "good to medium," "medium," "medium to poor," "poor," and "nil") and issued as a NOTAM(D)
  • When tower controllers have received runway braking action reports which include the terms poor or nil, or whenever weather conditions are conducive to deteriorating or rapidly changing runway braking conditions, the tower will include on the ATIS broadcast the statement, "BRAKING ACTION ADVISORIES ARE IN EFFECT"
  • During the time that braking action advisories are in effect, ATC will issue the latest braking action report for the runway in use to each arriving and departing aircraft. Pilots should be prepared for deteriorating braking conditions and should request current runway condition information if not volunteered by controllers. Pilots should also be prepared to provide a descriptive runway condition report to controllers after landing

Runway Friction Reports and Advisories:

  • Friction is defined as the ratio of the tangential force needed to maintain uniform relative motion between two contacting surfaces (aircraft tires to the pavement surface) to the perpendicular force holding them in contact (distributed aircraft weight to the aircraft tire area)
    • Simply stated, friction quantifies slipperiness of pavement surfaces
  • The Greek letter μ (pronounced “myew”), is used to designate a friction value representing runway surface conditions
  • μ (friction) values range from 0 to 100 where zero is the lowest friction value and 100 is the maximum friction value obtainable
  • For frozen contaminants on runway surfaces, a μ value of 40 or less is the level when the aircraft braking performance starts to deteriorate and directional control begins to be less responsive. The lower the μ value, the less effective braking performance becomes and the more difficult directional control becomes
  • At airports with friction measuring devices, airport management should conduct friction measurements on runways covered with compacted snow and/or ice
    • Numerical readings may be obtained by using any FAA approved friction measuring device. As these devices do not provide equal numerical readings on contaminated surfaces, it is necessary to designate the type of friction measuring device used
    • When the μ value for any one-third zone of an active runway is 40 or less, a report should be given to ATC by airport management for dissemination to pilots. The report will identify the runway, the time of measurement, the type of friction measuring device used, μ values for each zone, and the contaminant conditions, e.g., wet snow, dry snow, slush, deicing chemicals, etc. Measurements for each one-third zone will be given in the direction of takeoff and landing on the runway. A report should also be given when μ values rise above 40 in all zones of a runway previously reporting a μ below 40
    • Airport management should initiate a NOTAM(D) when the friction measuring device is out of service
  • When μ reports are provided by airport management, the ATC facility providing approach control or local airport advisory will provide the report to any pilot upon request
  • Pilots should use μ information with other knowledge including aircraft performance characteristics, type, and weight, previous experience, wind conditions, and aircraft tire type (i.e., bias ply vs. radial constructed) to determine runway suitability
  • No correlation has been established between μ values and the descriptive terms "good," "good to medium," "medium," "medium to poor," "poor," and "nil" used in braking action reports

Conclusion:

  • Pilots are responsible for advising ATC about breaking conditions

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