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320516 Wet and Dry V1

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  • 320516 Wet and Dry V1

    Hi,

    Q. During take-off on a limiting runway, if a dry V1 was used instead of a wet V1 due to a wet runway conditions the result would be?

    Wrong answer: Dry V1 and wet V1 are the same.

    Correct answer: The accelerate stop distance will exceed the accelerate stop distance available.


    I absolutely agree with the theory that stopping is harder when it's wet, but looking in CAP 698 I can't find a difference between wet and dry V1. E.g. in Fig 3.2 or Fig 4.8, and the regulation factor appears to be 1.0 for a 'wet paved' take off, so I'm not sure what's wrong with the 'wrong answer' above. Unless this is specifically referring to take off on wet grass, I'm at a loss. Please will someone point me to what I've not seen?

    Thanks.

  • #2
    If the runway is wet we need to reduce the dry V1 to a wet V1 because of the reduced braking coefficient so that we can stop within the the ASDA. If we use the dry V1 instead of the wet V1 then we will not stop within the ASDA.
    In the old days the standard reduction was 8 to 10 knots but now the ODM provides wet V1 tables and the reduction is as low as 3 to 4 knots.
    The CAP has no wet V1 tables because it is old generation.

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    • #3
      OK, thanks Colin, most helpful.

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