A/C off the runway in CPH

[tribo]

Re: A/C off the runway in CPH

Originally Posted by Empty Cruise

TheOddOne,

I therefore feel that the responsibility for determining the relationship between the FC (as measured by a given piece of test equipment) and the stop cabability of the A/C lies with the manufacturer (and the operator who applies the data) - end of story. They make the thing, they test it, they supply the data, we operate it.

Boeing "feel": (From 2003 Boeing Performance and Flight Operations Engineer Conference, Seattle, washington USA)

Question:
Does Boeing hava a position on how to relate runway friction chart information to reported braking action?

Response:
There are many different runway friction vehicles, which have not been calibrated to a standard measurement system nor the airplane. At this point Boeing does not correlate runway friction measurements to pilot reported braking actions or airplane braking coefficient.

Question:
Then how does (is) flight operations (to) determine what to use?

Response:
The slippery runway (landing and takeoff) data provided by Boeing is a function of airplane braking coefficient. Airplane braking coefficient is the percentage of the airplane's weight on the wheels (W-L) which is converted into an effective stopping force. For example, for a reported airplane braking coefficient of 0.20, an airplane with a (W-L) of 100,000 lbs would create 20,000 lbs of stopping force.

Boeing provides slippery runway data based on an airplane braking coefficient of 0.05 to 0.2 (Poor to Good reported braking action). Please review the following guidance for relating commonly used terms of reporting runway condition to airplane braking coefficient:

Followed by a table with headings:

1. Airplane Braking Coefficient
2. Pilot Reported Braking Action
3. Runway Description

And content:

1. 0.4
2. Approximates dry runway
3. Friction limited certification values

1. 0.2
2. Good
3. Wet Runway, Jar certification for compact snow

1. 0.1
2. Medium/Fair
3. Ice, Compacted Snow

1. 0.05
2. Poor/Nil
3. Wet Ice, Slush, Melting Compacted Snow, Standing Water

On a runway covered with wet ice, slush, melting compacted snow, or standing water the possibility of hydroplasning exists, which can result in nil braking capability. For that reason we recommend that the flight crew use the operational landing distance for POOR Braking Action in such conditions to determine the acceptability of landing on such a runway.

Airbus "feel"
Getting to grips with cold weather operations

http://www.wingfiles.com/

CORRELATION BETWEEN REPORTED MY AND BRAKING PERFORMANCEPlease bear in mind:

• Airports release a friction coefficient derived from a measuring vehicle. This friction coefficient is termed as "reported MY".
  The actual friction coefficient termed as the "Effective MY" is the result of the interaction tire/runway and depends on the tire pressure, tire wear, aircraft speed, aircraft weight and anti-skid system efficiency.
  To date, there is no way to establish a clear correlation between the "reported MY" and the "effective MY". There is even a poor correlation between the "reported MY" of the different measuring vehicles.
  
  It is the very difficult to link the published performance on a contaminated runway to a "reported MY" only.

• The presence of fluid contaminants (water, slush and loose snow) on the runway surface reduces the friction coefficient, may lead to aquaplaning (also called hydroplaning) and creates an additional drag.
  This additional drag is due to the precipitation of the contaminant onto the landing gear and the airframe, and to the displacement of the fluid from the path of the tire. Consequently, braking and accelerating performance are affected. The impact on the accelerating forces leads to a limitation in depth of the contaminant for takeoff.
  
  Hard contaminants (Compacted snow and ice) only affect the braking performance of the aircraft by a reduction of the friction coefficient.

1. Airbus Industrie publishes the takeoff and landing performance according to the type of the contaminant, and to the depth of fluid contaminants.

EASA "feel":
From NPA 14/2004 Operations on contaminated runways
http://www.easa.eu.int/doc/Rulemakin...PA_14_2004.pdf

7.3.3
Use of Ground Friction Measurement Devices

Ideally it would be preferable to relate aeroplane braking performance to a friction index measured by a ground friction device that would be reported as part of a Surface Condition Report. However, there is not, at present, a common friction index for all ground friction measuring devices. Hence it is not practicable at the present time to determine aeroplane performance on the basis of an internationally accepted friction index measured by ground friction devices. Notwithstanding this lack of a common index, the applicant may optionally choose to present take-off and landing performance data as a function of an aeroplane braking coefficient or wheel braking coefficient constant with ground speed. The responsibility for relating this data to a friction index measured by a ground friction device will fall on the operator and the operating authority.