There doesn't seem to be any shortage of braking action reports out there, but how much of it is usable? If presented with a μ number, an RCR, or just plain text "good, fair, poor" or something similar, how do you translate that to getting the airplane stopped?
— James Albright
Most of the answer relies in your aircraft flight manual, but it helps to understand what the rest of the world is talking about. The "RCAM" report adopted recently seems to help: Runway Conditions Codes. But a little background can be helpful.
U.S. ATC 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,” “fair,” “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 NOTAM purposes, braking action reports are classified according to the most critical term (“fair,” “poor,” or “nil”) used 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.
Source: Aeronautical Information Manual §4−3−8
When considering pilot reports, consider the aircraft type. It may seem counter intuitive, but it may actually be easier to stop a larger, heavier aircraft than a smaller one. More weight on the wheels can make it easier for a Boeing 747 to stop than a Cessna 150.
USAF Runway Condition Reading (RCR)
USAF has established RCR procedures for determining the average deceleration readings of runways under conditions of water, slush, ice, or snow. The use of RCR code is dependent upon the pilot's having a stopping capability chart specifically applicable to his/her aircraft. USAF offices furnish RCR information at airports serving USAF and ANG aircraft.
Source: U.S. FAA Order JO 7110.10W §4-4-3 ¶11
Our Air Force flight manual charts had performance numbers with Runway Condition Readings (RCR). An RCR of 23 was considered dry, 9 was wet, and 4 was icy. The exact number tends to change a few points here and there, but those are close. If you are at an airport with military airplanes, they might just have an RCR for you. Can you enter your chart with an RCR? Probably not. But it is more information than you had before you asked.
- MU (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 MU 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 MU value, the less effective braking performance becomes and the more difficult directional control becomes.
- When the MU 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.
- No correlation has been established between MU values and the descriptive terms “good,” “fair,” “poor,” and “nil” used in braking action reports.
Source: Aeronautical Information Manual §4−3−9
he Aeronautical Information Manual seems to discount any connection between MU and good/fair/poor/nil qualifiers and you hardly hear the term "mu" in the United States. But the ICAO calculated coefficient seems suspiciously similar.
SNOWTAM Format, from ICAO Annex 15 Appendix 2.
A SNOWTAM is a "Special Series NOTAM"
Information concerning snow, slush, ice and standing water on aerodrome/heliport pavements shall, when reported by means of a SNOWTAM, contain the information in the SNOWTAM Format in Appendix 2.
Source: ICAO Annex 15] ¶5.2.3
The takeoff data must be based on . . . At the option of the applicant, grooved or porous friction course wet, hard-surfaced runways.
Source: 14 CFR 25 §25.105(c)(1)(ii)
Accelerate-stop distance. . . . At the option of the applicant, a higher wet runway braking coefficient of friction may be used for runway surfaces that have been grooved or treated with a porous friction course material.
Source: 14 CFR 25 §25.109(d)
Additionally, at the option of the applicant, wet runway takeoff distances may be established for runway surfaces that have been grooved or treated with a porous friction course, and may be approved for use on runways where such surfaces have been designed constructed, and maintained in a manner acceptable to the Administrator.
Source: 14 CFR 25 §25.1533(3)
I've flown aircraft that allowed pilots to consider wet grooved runways to be essentially dry. The Gulfstream G450 does not. The performance section of that AFM does not mention runway grooves at all. The only thing in our books on the subject appears in G450-OIS-02. On page 19 it says: "For landing operations on a wet, grooved runway, data in this OIS will be conservative." This leads me to believe Gulfstream has not factored in grooved runways for the G450 and wants you to use it as a safety pad. There are test results available which lead one to believe that grooved runways do bring balanced field lengths on wet runways almost to the level of a dry runway and that substantially reduce landing distances. But all that goes out the window with any amount of slush. Curiously, the Gulfstream G150 does allow you to consider a wet grooved runway to be "effectively dry."
More about this: Grooved Runways.
14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation
Aeronautical Information Manual
FAA Air Traffic Organization Policy, Flight Services, Order JO 7110.10W, March 7, 2013
Gulfstream G450 Operational Information Supplement, G450-OIS-02, Contaminated Runway Performance, Revision 1, August 3, 2011
ICAO Annex 15 - Aeronautical Information Services, International Standards and Recommended Practices, Annex 15 to the Convention on International Civil Aviation, July 2010
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