braking action assessment

Several different types of friction testing machines in use. They determine (along with visual inspection) when we transfer from normal (dry or wet) performance figures to contaminated (or if really severe then runway closure). When the runway is considered to be contaminated then there are also other operational considerations (eg, no derated take off power, no departures with unserviceable brake units or thrust reversers, no tailwind take offs, etc, etc).

We used to use in the RAF a MU Meter trailer for measuring braking efficiency on the runway….

Aviation Braking Action Tables

Runway Friction Braking Action
Term Mu
Good .40 to 1.0
Medium to Good .36 to .39
Medium .30 to .35
Poor .26 to .29
Nil 0 to .25
Term Tapley RCR
Good 57 to 77 19 to 25
– – –
Fair 39 to 56 13 to 18
Poor 18 to 38 6 to 12
Nil 6 to 17 2 to 5

Warning: 25 RCR, 25 Tapley, and .25 Mu are not the same!

Nil braking indicates idle thrust is more than braking capability.

A “good” mu report may indicate only half the braking effectiveness of a dry runway.

Mu greater than .4 is reported in whole numbers (5, 6, etc).

RCR
runway condition reading
Numerical decelerometer readings relayed by air traffic controllers
at USAF and certain civil bases for use by the pilot in determining
runway braking action. These readings are routinely relayed only to USAF and Air National Guard Aircraft.

Hope this helps

A225HVY

I dont know all the technical details, but the braking action is measured as described. From memory I think they measure it in thirds and give a decimal reading. For example 0.7 – 0.6 – 0.4 .I assume this is out of 1.0.
The landing distance in these conditions is then assessed by the crew from the manual and the amount of braking applied accordingly.If the required distance is too great, then the aircraft cannot land.
It also depends on runway length.
I dont think the airport will be closed unless it falls below about 0.5. But I am only guessing.They will continue to try and improve the figures with brushing and de-icing.

I don’t know how they’d do a brake test, however at Luton they do a Grip test, they have this little wheel machine hooked up to the back of a batterd Land Rover Defender and a reading comes up in the car as to what the runway grip is

Sorry guys I think i’ve maybe put this in the wrong section is there any way I can move it to General Aviation?