Mu Readings

[heywatchthis]

Anybody have a chart that shows the conversion from MU readings to Braking action reports. I used to have one. I want to add it to our checklist, so the next time I am on short final and they give me BA reports in MU or some other format, I can relate.

Thanks,

 

[stupidpilot]

I think its in the AIM. Here's the breakdown:
Good: > 0.50
Fair: 0.35-0.50
Poor: 0.15-0.34
Nil: < or = 0.14

Hope that helps!

 

[Mercury]

Info from the AIM

4-3-9. Runway Friction Reports and Advisories
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 becomes.
d. At airports with friction measuring devices, airport management should conduct friction measurements on runways covered with compacted snow and/or ice.
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.​

 

[Dak]

Printable table

http://web.nbaa.org/public/ops/part135/200610brakingaction.pdf

 

[real swift]

There is also an article in the December 2006 issue of Business and Commercial aviation, p.30.

 

[Dak]

PhD version (ICAO)

http://www.jaa.nl/secured/GASR/Working Papers/WP 061 Appendix 3.pdf

I guess this is the background for how they came up with it.

 

[heywatchthis]

Excellent.

I love message boards. It's an unlimited supply of information.

Just what I was looking for and more.

THANKS

 

[Say Again Over]

Yes, and been a pilot for thirty years and have yet to use an mu.

 

[Dak]

They're coming.

I would have said the same last year but just last week the PANC ATIS had them. I've seen them elsewhere too recently. I think more in the international arena though. At ANC the last two times I was there (Dec) the Mu's reported were accurate for the actual conditions.

 

[RedGuy]

What ever happened to the simple, good, fair, poor, nil? That's alot easier to understand than a bunch of numbers that really don't mean anything unless you have a magic box to disseminate them.

 

[Coool Hand Luke]

What ever happened to the simple, good, fair, poor, nil? That's alot easier to understand than a bunch of numbers that really don't mean anything unless you have a magic box to disseminate them.

Actually, MU values are (supposed to be) only reported if MU values are 40 or below. If the ATCT also receives at braking action report(s) from pilots it/they are also given to subsequent landing aircraft. In other words: you get both reports. The more information the better if you ask me.

Personally I prefer MU reports to good, fair, poor or nil reports. As you know, no one wants to be the guy the shuts an airport down by reporting braking action as nil, so crew braking action reports are often under-reported. Not to mention the EMB-120 I fly stops much easier on a contaminated runway than the Citation VII that I also fly. In other words, a good report in the EMB-120 could be a poor in the Citation VII. With a Tapley Meter or SAAB or whatever, I know what I am dealing with and it takes aircraft tire condition, aircraft types, crew technique, etc. out of the equation.

 

[SDCFI]

The first time I encountered Mu reports was in Helena, MT of all places. I liked them for two reasons 1) If there's no pilot BA reports you might get one from an airport vehicle. Do you really trust Jim Bob in his pickup to give you an accurate indication of how your airplane is going to stop? The Mu reading is a calculated measure of runway friction, not someone's opinion. 2) You get 3 readings so you can anticipate your braking and plan your touchdown accordingly based on what part of the runway has the best braking action. I say bring 'em on.

 

[Coool Hand Luke]

The first time I encountered Mu reports was in Helena, MT of all places. I liked them for two reasons 1) If there's no pilot BA reports you might get one from an airport vehicle. Do you really trust Jim Bob in his pickup to give you an accurate indication of how your airplane is going to stop? The Mu reading is a calculated measure of runway friction, not someone's opinion. 2) You get 3 readings so you can anticipate your braking and plan your touchdown accordingly based on what part of the runway has the best braking action. I say bring 'em on.

Yes. It's also important to note that those three readings are actually averages from 9 separate readings (3 each in the touchdown, midpoint and rollout zones).

For example, airport operations conducts a braking action report and finds that the touchdown MU values are 35, 31 and 33 respectively for an average of 33. This will be reported as an overall touchdown MU value of 35 as the final averaged MU value is rounded to the nearest 0 or 5 (ie. 33 reported as 35, 32 reported as 30).

 

[RedGuy]

Yes, but I still think they could be reported in a simpler manner with good, fair, poor, nil. Rather than the numbers, that's just my opinion though and now it's not as bad since it's been explained alittle better.

 

[stupidpilot]

Yes, but I still think they could be reported in a simpler manner with good, fair, poor, nil. Rather than the numbers, that's just my opinion though and now it's not as bad since it's been explained alittle better.

Looking at all the possible ways for braking action reports(Mu, skiddometer,James-branke index, Decel Meters2 etc.) The overriding theme is the bigger the number the better the braking action. They are all very similar in how they report the braking action values except for the ICAO index which reports it in whole numbers.