getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(55)

aircraft. The adopted method was to conduct some tests with real aircraft and to compare
the results with those obtained from measuring vehicles.

Results demonstrated poor correlation. For instance, when a Tapley meter reads 0.36, a
MU-meter reads 0.4, a SFT reads 0.43, a JBD 12...
To date, scientists have been unsuccessful in providing the industry with reliable and
universal values. Tests and studies are still in progress.

As it is quite difficult to correlate the measured μ with the actual μ, termed as effective μ,
the measured μ is termed as .reported μ..
In other words, one should not get confused between:
1/ Effective μ: The actual friction coefficient induced from the tire/runway surface
interaction between a given aircraft and a given runway, for the conditions of the day.
2/ Reported μ: Friction coefficient measured by the measuring vehicle.

● Particularities of fluid contaminants
Moreover, the aircraft braking performance on a runway covered by a fluid contaminant (water, slush and loose snow) does not depend only on the friction coefficient μ.
As presented in chapters C2.2
 and C2.3,
 the model of the aircraft braking performance (takeoff and landing) on a contaminated runway takes into account not only the reduction of a friction coefficient but also:
-
The displacement drag

-
The impingement drag

These two additional drags (required to be taken into account by regulations) require knowing the type and depth of the contaminant.
In other words, even assuming the advent of a new measuring friction device providing a reported μ equal to the effective μ, it would be impossible to provide takeoff and landing performance only as a function of the reported μ. Airbus Industrie would still require information regarding the depth of fluid contaminants.
C3.4.3 Data provided by Airbus Industrie
Please refer to § C6
 for further details on contaminated runway performance provided by Airbus Industrie.
● Hard contaminants
For hard contaminants, namely compacted snow and ice, Airbus Industrie provides the aircraft performance independently of the amount of contaminants on the runway. Behind these terms are some effective μ. These two sets of data are certified.
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● Fluid contaminants
Airbus Industrie provides takeoff and landing performance on a runway contaminated by a fluid contaminant (water, slush and loose snow) as a function of the depth of contaminants on the runway.
For instance, takeoff or landing charts are published for .1/4 inch slush., .1/2 inch slush., .1/4 inch water. and .1/2 inch water.. For loose snow, a linear variation has been established with slush.
In other words, pilots cannot get the performance from reported μ or Braking
Action.
Pilots need the type and depth of contaminant on the runway.
　
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