Originally Posted by
galaxy flyer
... There is a reasonable assumption that -500’ MSL is good enough and lower PA is unlikely...
..which of course does not account for, say, Bar Yehuda Airport, -1240 feet MSL (Dead Sea region of Israel).
It's not a limitation for a dude in a 172, who can take off at any pressure altitude he darn well wants to try. (I won't bore you with the war stories)
But for flights that
legally require TO calculations involving PA, if the charts, graphs and databases have a floor of -500 feet, simply for reasons of "why bother going lower?", then those pilots are limited to what they can calculate for.
It is sort of the flip side of the temperature ceilings that prevent some planes flying out of PHX on hot days. I'm sure they
could successfully take off even at 52°C - but the charts don't go that high, so they can't do the legally-required calculations for that temperature, so they are grounded: 52°C (or -505 feet PA) lie in the "Here be dragons" regions.