[Quik289]

When it's this hot the air is not "dense" enough to provide the same lift that you get on a nice cool morning. Definitely a good thing they are doing the math. The calculation is, of course, most critical for take offs, or you'll be kissing the ground just past the end of the runway. Same reason your Cobra won't make as much horsepower on those roasting hot days as it will on a cool fall or spring morning - air is too thin! I note you were posting at 5 PM, hottest time of the day. Be glad they didn't decide to wait for midnight!