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EnzoC · 5th September 2008, 13:53

@sixfeetabove

As Old Smokey already stated, there is no general answer to what is limiting on a wet runway. You have to look at each case individually.
Factors are certification, aircraft type (number of engines), speed (V1) concept, airline policy, runway.
Dry runway T/O is based on no reverser and 35ft screen height, where wet runway T/O allows to account for the reverser and reduces screen height to 15ft. Thus, you might end up in a situation, where the dry runway T/O is more limiting than the wet runway T/O (same other parameters). Authorities addressed this point and require on a wet runway a crosscheck of the wet and dry data and the use of the lower weight.
In other words: you might calculate a wet RWY T/O and find out, that you are limited by the dry RWY field length limit, which, for a four engine aircraft usually is the all-engine-go case (due to the 15% penalty).

Wet/contaminated runway data have not been required for FAA certification. The data could be found in the "Performance Engineers Manual PEM" as advisory or guidance information only, but never really made it to the Airplane Flight Manual. For younger FAA certified aircraft you will find the data in the AFM, but they are still advisory information.

I recall a Boeing recommendation for B747-200 to knock of 10kts from V1 on wet runway without a weight decrease necessary.

Hope that helps a bit.

5th September 2008, 13:53	#18 (permalink)
EnzoC Join Date: Jan 2008 Location: Germany Posts: 9	@sixfeetabove As Old Smokey already stated, there is no general answer to what is limiting on a wet runway. You have to look at each case individually. Factors are certification, aircraft type (number of engines), speed (V1) concept, airline policy, runway. Dry runway T/O is based on no reverser and 35ft screen height, where wet runway T/O allows to account for the reverser and reduces screen height to 15ft. Thus, you might end up in a situation, where the dry runway T/O is more limiting than the wet runway T/O (same other parameters). Authorities addressed this point and require on a wet runway a crosscheck of the wet and dry data and the use of the lower weight. In other words: you might calculate a wet RWY T/O and find out, that you are limited by the dry RWY field length limit, which, for a four engine aircraft usually is the all-engine-go case (due to the 15% penalty). Wet/contaminated runway data have not been required for FAA certification. The data could be found in the "Performance Engineers Manual PEM" as advisory or guidance information only, but never really made it to the Airplane Flight Manual. For younger FAA certified aircraft you will find the data in the AFM, but they are still advisory information. I recall a Boeing recommendation for B747-200 to knock of 10kts from V1 on wet runway without a weight decrease necessary. Hope that helps a bit.