Understanding braking condition Pireps

BRAKING ACTION
PIREPS
When braking action conditions less than Good are encountered, pilots are expected to provide a PIREP based on
the definitions provided in the table below. Until FAA guidance materials are revised to replace the term Fair with
Medium, these two terms may be used interchangeably. The terms “Good to Medium” and “Medium to Poor”
represent an intermediate level of braking action, not a braking action that varies along the runway length. If braking
action varies along the runway length, such as the first half of the runway is Medium and the second half is Poor,
clearly report that in the PIREP (e.g., “first half Medium, last half Poor”).


CORRELATING EXPECTED RUNWAY CONDITIONS
The correlation between different sources of runway conditions (e.g., PIREPs, runway surface conditions and Mu
values) are estimates. Under extremely cold temperatures or for runways that have been chemically treated, the
braking capabilities may be better than the runway surface conditions estimated below. When multiple sources are
provided (e.g., braking action medium, runway covered with ice and runway Mu is 27/30/28) conflicts are possible. If
such conflicts occur, consider all factors including data currency and the type of airplane a PIREP was given from. A
valid PIREP or runway surface condition report are more reliable indicators of what to expect than reported runway
Mu values.


Runway Friction Mu Reports
Mu values in the U.S. are typically shown as whole numbers (40) and are equivalent to the ICAO standard decimal
values (.40). Zero is the lowest friction and 100 is the highest Mu friction. When the Mu value for any one­third 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). While the table
below includes information published by ICAO correlating runway friction measurements to estimated braking actions,
the FAA cautions that no reliable correlation exists. Runway Mu values can vary significantly for the same
contaminant condition due to measuring techniques, equipment calibration, the effects of contamination on the friction
measuring device and the time passage since the measurement. Do not base landing distance assessments solely
on runway Mu friction reports. If Mu is the only information provided, attempt to ascertain the depth and type of
runway contaminants to make a better assessment of actual conditions.

Braking Action Term

Definition

Aircraft Reaction

(Pilot Reporting Guide)

ICAO Code

Runway Surface Condition

MU

(runway MU)*

 

Good

More braking capability is available than is used in typical deceleration on a non-limiting runway (i.e., a runway with additional stopping distance available). Directional control good.

 

5

Wet runway with a water depth of 1/8” or less

Compacted snow with OAT below -15ºC

¾” or less of dry snow

0.40 & above

Medium to Good

 

 

4

 

0.36 – 0.39

Medium

Noticeably degraded braking condition. Expect and plan for a longer stopping distance such as might be expected on a packed or compacted snow–covered runway. Effective directional control.

 

3

Compacted and sanded snow

Compacted snow with an OAT above -15ºC

Sanded ice

0.30 – 0.35

Medium to Poor

 

 

2

 

0.29 – 0.26

Poor

Very degraded braking condition (a potential for hydroplaning). Expect and plan for a significantly longer stopping distance such as might be expected on an ice-covered runway. Directional control minimally effective.

 

1

Wet snow

Slush

Wet runway with a water depth more than 1/8”

Heavy rain

Ice

0.25 & below

Nil

Braking action is minimal to non-existent and/or directional control uncertain.

(Max) Thrust reverser utilized until stop. Directional control dependant on aerodynamic forces only (modulated TR use). Poor directional control even while taxiing. Full brake application with little or no effect. (Full anti-skid cycling throughout rollout.)

 

Wet Ice

 

 

 

And a great article/PDF from Flight Safety

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James Horvath Gooey Website
James Horvath Gooey Oooey