Mu-Meter into RCR?

[StopStart]

Does anyone have or know where I can find a table to accurately covert a Mu-Meter reading into an RCR?
The RAF Flight Information Handbook has a vague chart but not one from which one can extract an accurate RCR figure.

Ta :)

[alatriste]

It is just an easy question: What does RCR stand for?
REGARDS

[StopStart]

Runway Condition Report

A measure of the level of contamination/braking action on a runway

:)

[andyb79]

runway condition reading i think

but i have been known to be wrong :=

[HotDog]

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.

[OverRun]

Got this USAF chart. Note that the decelerometers such as Tapley are for compacted snow and ice - not for wet pavements. Rather think I prefer Hot Dog's numbers and definitions in the above article.

Also I strongly believe that friction testing should be conducted at appropriate speeds to measure the effects of microtexture and macrotexture. For runways, that means testing at high speed - such as 100-160 kph (60-100 mph). IMHO the results for slow speed tests are just plain rubbish on runways. If the testing is done at 65 kph (as per the US chart), then it will give erroneous readings and there'll be a few aircraft running off the end . . . . . . . . .

http://www.kubu.net/aviation/friction_chart.jpg

[HotDog]

A brand new Saab ground test vehicle ran off the end of RW13 at Kai Tak some years ago. I guess he must have been doing about 100mph. Hong Kong CAD were very tight lipped about it at the time.:D

[OverRun]

I've ditched the Mu-Meter tow-vehicle before at speed. Then Uli ran it off the end of Essendon at speed (that dates things) and went down the slope, across the road, and into the fence. . . At least it was raining for him. I had no such excuse. It is still important to test at the right speed, even if airport engineers aren't always up to the driving skills required.

Mind you, it is all grist to the mill of the court's "reasonable man" test. It is obvious that no reasonable man would travel down a runway at 100 mph in a machine. Far too dangerous. umm - that is a joke

Having made the jokes, all credit to Hong Kong for testing and testing properly and at the right speeds - more than quite a few other big-name airports do. I have been humbled before by the first class work done by some Asian Civil Aviation Departments and will no doubt be humbled again.

[Shore Guy]

I wrote this piece on MU readings/runway contamination for our in house publication......

RUNWAY FRICTION (MU) MEASUREMENTS:

BEWARE

In the course of reviewing a recent industry runway excursion (U.S), it has become apparent that there is a major discrepancy between airports and the methods used in measuring and reporting runway friction values. The purpose of this article is to make crews aware of these discrepancies and to be cautious in using reported “MU” values as a primary indication of braking action.

In an effort to standardize with I.C.A.O., the FAA has begun to report braking action in a quantifiable way, using the “MU” value. MU values range from 0 to 100, where 0 is the lowest friction value and 100 is the theoretical maximum friction value obtainable. There is an “estimated” correlation between MU values and the historical braking action reports of good, fair, poor, and nil.

MU readings are normally provided, where available, to the crew by ATC in the form of NOTAM, ATIS, or tower. One measurement is taken on each third of the runway, resulting in a report for three segments of the runway. Normally MU values are reported only when values fall below an MU of 40, this being the baseline number where braking performance deteriorates.

All of this sounds good and quite scientific in its approach, however there have proven to be some major discrepancies in how these values are measured, charted, and reported. There are two primary ways to measure an MU value. One is by the “Continuous Friction Measuring Equipment” (CFME), and is the preferred method. An example of this is the Saab Friction Tester (the car that looks like it is dragging a bicycle tire behind it). The other method of measuring MU is using either an electric or mechanical decelerometer. There are multiple manufacturers of these devices, and their measurements, scales and charts are only guaranteed to provide a “nearly equivalent” correlation to MU values.

Other limitations of using an MU value as a primary indication of runway friction are:

(1) Runway friction measurements are taken only on the center section of the runway (10 feet from centerline for narrow body operations, 20 feet for wide body operations), so the tested area is only a small part of the total runway surface.

(2) If the runway MU values are measured by decelerometer, its readings are affected by the deceleration characteristics of the vehicle it is mounted to. There is no standard. (The same can be said of aircraft – different aircraft types have different deceleration characteristics).

(3) The airport operator shoulders the responsibility of conducting and reporting runway friction tests to ATC. Data once again shows inconsistencies between how different airport operators conduct these tests and report their results.

(4) The CAA of Great Britain has issued a bulletin (FODCOM 17/2001) to eliminate reporting of (measured) runway friction in slush and thin deposits of wet snow. “The Authority is aware that the runway friction measuring machines currently available do not give a reliably accurate reading in conditions of slush or thin deposits of wet snow”.


In preparing for this article, I consulted information from the FAA (AIM, regulations, and advisory circulars), CAA (U.K.), CTA (Canada), our own and other airline FOM’s, Jeppesen “J-Aid”, and material from the manufacturers of various friction measuring devices. The main consistency I found among these materials was their inconsistency.

This is not to say that runway friction measurements should be totally disregarded during contaminated runway operations. It is just to emphasize that there are limitations to relying on what appears to be, by way of measurement and numerical values reported, a “scientific” approach to measuring surface friction. In the real world, braking action and directional control are affected by numerous other factors that are aircraft specific such as aircraft geometry, tire pressures, CG, brake pack wear, etc. As mentioned in one of the referenced materials, braking action reported as poor by an F-100 may be good to a B-757.

The nature of our operation presents some interesting challenges in this regard. Our next day operation results in our aircraft sometimes being the first transport category aircraft in hours to use a contaminated runway, with the lack of recent braking action reports from other transport aircraft. An MU value may be the only indication provided to the crew in these circumstances, and as indicated above, these values are sometimes suspect. It is in these circumstances that we become part line pilot/part experimental test pilot.

Make sure to provide ATC with a braking action report under these circumstances or any time you experience degradation from reported conditions.