The readings they are giving are the runway friction readouts given in mu values. Based on our operating specifications we have to increase the max runway landing distance based upon
different friction readings.
These are directly out of my airline operations manual:
They are as follows:
1) These examples show that some segment values may be above the value of
40 and still be contained in a NOTAM D.
2) Friction measuring reports are to be expressed using the name of the FAA
approved device, followed by the “MU” (pronounced “mew”), followed by the
reported values and the time of the measurement.
3) Use the following abbreviations to indicate the type of friction measuring
device used:
BOW Bowmonk Decelerometer
BRD Brakemeter-Dynometer
ERD Electronic Recording Decelerometer
GRT Griptester
MUM Mark 4 Mu Meter
RFT Runway friction tester
SFH Surface friction tester (high pressure tire)
SFL Surface friction tester (low pressure tire)
SKH Skiddometer (high pressure tire)
SKL Skiddometer (low pressure tire)
TAP Tapley Decelerometer
B. These readings are available on request from the airport control tower.
C. Mu-reading values in relation to braking conditions are as follows:
Measured Coefficient of Friction Descriptive Word
0.40 and above Good
0.39 to 0.35 Medium to Good
0.34 to 0.30 Medium
0.29 to 0.25 Medium to Poor
0.24 to 0.20 Poor
0.19 to 0.0 Nil
Table 12 - 2
MU Reading Values
NOTE
Values are reported for the first third (touchdown), second third and last third
(roll-out) of the runway. Values above .40 are given in tenths as a single
digit. The range of values below .40 are indicative of deteriorating conditions
and are given in hundredths as a group number.
D. Measurement. The depth is always expressed in terms of thin (less than ¼ inch),
¼ inch, ½ inch and 1 inch. When one inch is reached, additional reports should be
in multiples of one inch and the use of fractions discontinued. If a variable amount
is reported, such as three to five inches, show the greater depth. When a snow
depth of 35 inches is reached, additional reports should be in multiples of feet only.
If a report is halfway between two reportable values, round to the next higher
reportable value.
E. Every snow NOTAM shall have the time that the conditions were observed by the
airport operator as the last element of the NOTAM. If no time given, inquire as to
when the condition was observed, if still unable to obtain a time, use the time when
the NOTAM information was given to the flight service specialist.
F. The correlation between different sources of runway conditions (i.e.; PIREPs,
runway surface conditions and Mu values) are estimates. A valid PIREP or runway
surface condition report are more reliable indicators of what to expect than reported
runway Mu values. If Mu is the only information provided, attempt to ascertain the
depth and type of runway contaminants, or aircraft braking action report to make a
better assessment of actual conditions, Mu values alone may significantly
overstate aircraft braking potential. (AC 91-79)
I hope this clears up some of your questions concerning airline operations during reduced friction operations.
