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4-3-9. Runway Friction Reports and
a. 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.
b. The greek letter MU (pronounced "myew"), is
used to designate a friction value representing
runway surface conditions.
c. 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
d. At airports with friction measuring devices,
airport management should conduct friction mea-
surements on runways covered with compacted snow
1. 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.
2. 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. The report will identify the runway, the time of
measurement, the type of friction measuring device
used, MU 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 MU values rise above 40 in all zones of a
runway previously reporting a MU below 40.
3. Airport management should initiate a NO-
TAM(D) when the friction measuring device is out of
e. When MU 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.
f. Pilots should use MU information with other
knowledge including aircraft performance character-
istics, type, and weight, previous experience, wind
conditions, and aircraft tire type (i.e., bias ply vs.
radial constructed) to determine runway suitability.
g. No correlation has been established between
MU values and the descriptive terms "good," "fair,"
"poor," and "nil." Effective October 1, 2016, these
terms will be replaced with "good," "good to
medium," "medium," "medium to poor," "poor," and
"nil" in braking action reports.
4-3-10. Intersection Takeoffs
a. In order to enhance airport capacities, reduce
taxiing distances, minimize departure delays, and
provide for more efficient movement of air traffic,
controllers may initiate intersection takeoffs as well
as approve them when the pilot requests. If for ANY
reason a pilot prefers to use a different intersection or
the full length of the runway or desires to obtain the
distance between the intersection and the runway end,
THE PILOT IS EXPECTED TO INFORM ATC
b. Pilots are expected to assess the suitability of an
intersection for use at takeoff during their preflight
planning. They must consider the resultant length
reduction to the published runway length and to the
published declared distances from the intersection
intended to be used for takeoff. The minimum runway
required for takeoff must fall within the reduced
runway length and the reduced declared distances
before the intersection can be accepted for takeoff.
AIM, Paragraph 4-3-6 , Use of Runways/Declared Distances
c. Controllers will issue the measured distance
from the intersection to the runway end rounded
"down" to the nearest 50 feet to any pilot who
requests and to all military aircraft, unless use of the
intersection is covered in appropriate directives.
Controllers, however, will not be able to inform pilots
of the distance from the intersection to the end of any
of the published declared distances.
FAA Order JO 7110.65, Paragraph 3-7-1, Ground Traffic Movement
Airport Operations 4-3-13