Wet Runway V1 Speed Reduction

[fdgolf]

Hi there,

Let us assume a long runway here at sea level (ie 11000 feet). Let us assume it is raining and the runway is WET. Let us finally assume we take off with an empty aircraft on a positional flight somewhere no too far, meaning our aircraft is not anywhere near our MTOW. Our airport performance chart tells us that by flexing our take off thrust we can get the aircraft airborne at our MTOW.

Now, since we are very light, do you reduce yor V1 speed for wet runway, or simply you just don't since we can get the aircraft out at its MTOW? (Hope I do not mislead anyone here).

Thanks in advance.

Cheers

[mutt]

In our case, the answer is yes. The WET runway correction is applied.


Mutt

[Old Smokey]

You will be obliged to use the Wet runway performance data, as the performance profiles for either Wet or Dry are so different. It's not just the difference in Reverse Thrust credits, lower screen height etc., but other factors such as reduced acceleration in the Takeoff roll to Vef etc. which are considered for the particular environmental condition.

Even though common sense says that, at the very light weight, you should be able to achieve Takeoff using Dry runway data, it's unproven, and legally, you would not have a leg to stand on at the enquiry.

Regards,

Old Smokey

[BEagle]

On the jet I used to fly, we would often do the following for runways when we weren't certain how wet/damp/dry the RW really was:

Given the actual conditions of OAT, QNH, W/V and RW length, calculate the MTOW which would be possible on a dry RW, calculate V1, apply the wet correction, note the result. (e.g. 127 -10 = 117)

For the ATOW, work out the dry V1. (e.g. 114)

Use the lower of the 2 results obtained. In the case above, 114.

But this was only safe if the same thrust setting was used for both cases. In our case it was; for other a/c it may not be.

[411A]

Done a long time ago...

Interesting idea BEagle.

This was done with every operator of the B707 that I worked for, and works well for the Lockheed tri-motor as well.

However, as you have pointed out, different strokes for different folks/aircraft/operators.

[fdgolf]

Thank you all for these interesting replies.

I also like BEagle's solution, but given that Old Smokey introduced the word "legaly"...

I usually take the Wet Data no matter what weight we take off at, simply to have the habbit for wet runways and using the appropiate data pages as well.

Anyone with additional comments?

Cheers

[oldebloke]

Not bad on a generous runway(spare distance),but remember the 15' screen height on limiting lengths(AMJ25X1591para3.2.1.b)
cheers...

[Old Smokey]

fdgolf,

I usually take the Wet Data no matter what weight we take off at

I hope that you were referring to wet runways only, as the reverse legal argument applies in that you may not use Wet runway data on a Dry runway.

Wet runway performance data offers 2 major concessions against the 'Normal' Dry runway rules, that is -

(1) Full credit is used for Reverse thrust in the Accelerate-Stop, and

(2) Screen height is reduced from 35 feet to 15 feet.

Dry runway certification REQUIRES a screen height of 35 feet, and that one means of retardation (usually Reverse Thrust) be kept in reserve for the Accelerate-Stop. If you plan a Takeoff on a Dry runway taking credit for Reverse thrust, and for a reduced screen height of 15 feet (which you would be doing if using Wet runway data), then you are in breach of the regulations. Aside from the legal angle, you would be eliminating all of the (quite small) safety margins offered by using Dry runway performance.

Remember that the Wet runway allowances are CONCESSIONS allowed against the normal safety margins in the 'unusual' circumstance of a wet runway.

Regards,

Old Smokey

[fdgolf]

Old Smokey,

Yes, Wet Data for when RW is wet, dry for when it is dry.

Regards,

fdgolf

[donstim]

And the speeds should always be that associated with the ATOW, wet or dry.