Deciphering Winter NOTAMs

If you customarily fly in warm, sunny climes you may not be familiar with some of the winter-weather contractions found in NOTAMs.

Last night the Seattle area experienced moderate snow followed by steady rain. Today’s NOTAMs for KPAE included these entries:

RWY 16R VER MU 43/45/39. 12 JAN 15:10 2011 UNTIL UFN. CREATED: 12 JAN 15:31 2011
TWY C,W,G,F 2 IN SN. 12 JAN 14:51 2011 UNTIL UFN. CREATED: 12 JAN 14:52 2011
RWY 16R/34L THN PTCHY SLR. 12 JAN 14:52 2011 UNTIL UFN. CREATED: 12 JAN 14:532011

“THN PTCHY SLR” is easy enough: thin patchy slush on runway 16R/34L. Taxiways C,W,G and F have two inches of snow. The MU entry is slightly more involved. “Mu” is used to report the runway’s surface friction quantities, or more simply, how slippery the runway is.

Section 4.3.9 in the FAA AIM  explains this with more depth: a Mu of 0 is the lowest friction value, and 100 is the highest. Mu of 40 or lower indicates a level where braking and directional control deteriorate.

The first entry in “VER MU 43/45/39” denotes the type of recording equipment in use. You can reference page 5 of the FAA’s Winter NOTAM Reporting PDF to determine that VER stands for Vericom VC3000:

BOW	Bowmonk Decelerometer (Bowmonk Sales)
BRD	Brakementer-Dynometer
ERD	Electronic Recording Decelerometer (Bowmonk)
GRT	Griptester (Findlay, Irvine, LTD)
MUM	Mark 4 Mu Meter (Bison Instruments, Inc.)
RFT	Runway friction tester (K.J. LAW Engineers)
SFH	Surface friction tester (high pressure tire) (SAAB, Airport Surface Friction Tester AB)
SFL	Surface friction tester (low pressure tire) (SAAB, Airport Surface Friction Tester AB)
SKH	Skiddometer (high pressure tire)(AEC, Airport Equipment Co.)
SKL	Skiddometer (low pressure tire) (AEC, Airport Equipment Co.)
AP	Tapley Decelerometer (Tapley Sales)
VER	Vericom (VC3000)

The three separate numbers following the MU denote the friction values for the three thirds of the runway, or as the AIM says, “for each one-third zone…in the direction of takeoff and landing on the runway.” Thus 16R’s first third’s Mu is 43, the middle third’s Mu is 45, and the last third is 39.

The NOTAM information above would, in summary, indicate a runway with a fair amount of contamination having relatively significant impact to aircraft controllability and braking.

In addition to the Winter NOTAM PDF above, I recommend you download this PDF of Approved NOTAM Contractions for the days when you encounter unfamiliar contractions.

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One thought on “Deciphering Winter NOTAMs

  1. Thanks! some more info:

    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.

    Rule of thumb for MU Value Braking Action:
    40 or greater is Good
    30 to 40 is Fair
    20 to 30 is Poor
    20 or less is Nil

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