I saw that relative humidity factor in the calculator and I've heard other people whom I respect talk about it, but I'd like to know exactly how humidity affects DA. Not "why" as I understand that humid air is less dense, but, numerically - how?
I've written manuals for, flown, instructed on, or consulted in flight ops on A-320, A-330, B-727, B-737, B-757, B-767, BAe-146, DC-3, DC-9 and MD
-80 as well as turboprops at half a dozen airlines and I have never once seen a performance chart that had an entry for humidity.
I believe strongly in getting to know the performance charts that are available for your airplane. I once taught an ATP written exam prep course and had two students in this class. One was a fifty-something businessman who owned a C-421 and the other student was a U-2 pilot.
Normally you kind of teach to the middle of the class. In this case there was no middle! The businessman had never once in twenty years with a license so much as looked at the performance charts for one of his airplanes. The U-2 pilot was an instructor pilot in his plane and lived (or died) with those charts. Fortunately he was sharp enough to get what I was teaching him, and still have time and neurons left over to help the other student or we'd have never gotten through the subject.
Still I would bet that the businessman never worked up the nerve to take the test. He probably just continues to stuff his plane full of people and bags and skis and head for the high elevation airports around the west.
Happiness is not seeing another trite Ste. Maarten photo all week long.