"737 Performance Reference Handbook" question

[D-OCHO]

In the "737 Performance Reference Handbook" the author makes a statement. And I quote:

The TOW on a wet runway must not exceed that permitted for a takeoff on a dry runway under the same circumstances. Therefor a Dry Check is required to exclude the theoretical possibility that, due to credits for reverse thrust and use of a reduced screen height, a higher TOW is obtained on a wet runway than on a dry runway, which is not allowed.

My questions are:

• What is the source of this underlined statement? (Boeing, regulatory etc.)
• Is this also applicable to an Improved Climb take-off?

[FlyingStone]

EASA AIROPS CAT.POL.A.205 is the requirement and is applicable to all takeoffs.

[Le Flaneur]

Due to the rules used to determine wet runway takeoff distance (Accelerate-go to a screen height of 15 feet on wet runway vice a 35 foot screen height for a dry runway) and use of thrust reverse credit for calculating the wet runway accelerate-stop distance, it is possible for the calculated wet runway takeoff distance to be less than the calculated takeoff distance for a dry runway. This is clearly an artifact of the rules used to calculate the wet runway takeoff performance, not actual aircraft performance. Therefore the rules require that the wet takeoff distance >= dry takeoff distance.

References:
FAA Wet Takeoff Performance Video (see discussion starting about 5:00)
https://www.youtube.com/watch?v=vEc_M9PqUJc&feature=emb_logo


Boeing Document D6-1420, Jet Transport Performance Methods

[D-OCHO]

Ok reason I ask if this is also applicable to Improved Climb is that last week I checked the TOW between a WET runway and a DRY runway and for the same Runway, same Temperarture, same QNH, same Slope I had a WET TOW of 77 Ton and a DRY TOW of 75,8 Ton.
Now as I read the rule I am limited by the DRY runway TOW of 75,8 Ton on a WET runway.

[Banana Joe]

You are also not allowed to use a clearway for calculations in wet conditions.

[FlightDetent]

Originally Posted by D-OCHO

Ok reason I ask if this is also applicable to Improved Climb is that last week I checked the TOW between a WET runway and a DRY runway and for the same Runway, same Temperarture, same QNH, same Slope I had a WET TOW of 77 Ton and a DRY TOW of 75,8 Ton. Now as I read the rule I am limited by the DRY runway TOW of 75,8 Ton on a WET runway.

Yes.

The algorithm (rules) for wet runway calculation has some of the conservative buffers within removed, compared to the dry one. This is done to obtain wet results that are not operationally (cash) crippling. The reasoning is that statistically, we operate from wet surfaces far less often, and for a limited exposure some of the margins could be relaxed. (How probable is to get OEI + WET + perf. limiting ops, at the same time).

Now and then mathematically it is possible to obtain a higher performance-limiting weight using the wet algorithm. Not the intention of the regulator, and so a "the loweset of" rule will apply.