Thanks John, yes as usual you are technically correct, and every situation will be different, with lots of variables, but after around 14,000 hours on one type , and this is not a technical argument, most pilots will have an idea whether it is SAFE or not to proceed with a given situation, not having full verified data.However as always this exposes you to possible litigation if anything goes wrong.....or worse.I have been forced into making such a decision three times so far in a very big jet.