Originally Posted by
Mad (Flt) Scientist
hmm
Given that Boeing grandfathered a bunch of stuff on the later 737s, I wonder if their performance data is also grandfathered. Data on other than dry runways used to be optional, rather than required for certification. In which case there will be no specific rules about scheduling V1 ...
To answer the original question:
It isn't as "safe" as your normal operations on dry, in that indeed, you are not guaranteed to be able to stop in the case of an engine failure between your V1stop and the V1 you're actually using. It would indeed be prudent to reduce the weight a bit to buy back that margin.
But, there's no hard line in the sand for much of certified performance - no matter how much we kid ourselves by quoting distances to the foot and scheduled speeds to the tenth of a knot! (I've seen both in worked examples in flight manuals, and it's frankly farcical). So in fact it is "safe" because we don't have to dig a bunch of airliners out of overrun areas every spring. By which I mean that operational experience indicates that in practice the reduction in safety margins compared to the "dry" case is justified by the absence of an effect on accident rates.
Its exactly the same logic as for reduced wet screen heights, allowed use of all braking devices on wet runways, assumption of zero x-wind for Vmcg, and so on.
Thanks MFS.
I'd agree with you, as I think the safety margins probably would be very conservative.
However I would be interested to see how I would stand legally if there WAS an overrun. Have I misinterpreted the rules - when the OM tells me to set V1=Vmcg, is that actually telling me to increase the t/o weight to raise the V1(contam) until it equals Vmcg, or just use Vmcg INSTEAD of V1(contam)?