With record heat in the forecast, pilots and passengers are remembering back to that 122-degree day in 1990 when it was so hot that jets couldn't take off from Sky Harbor International Airport.

Some often wonder if it could happen again. The answer, according to American Airlines, is “yes and no.”

Airplanes don’t perform as well in thin air and air gets thinner when temperatures rise. The hotter the temperatures, the longer an airplane will spend on the runway trying to get up to takeoff speed.

Pilots know exactly how much runway they need for takeoff thanks to detailed performance charts. In 1990, none of those charts went above 120 degrees.

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"You could extrapolate and you could guess. [But] we don't fly passengers around on guesswork,” said Jim Tilmon, an aviation expert and former American Airlines pilot. “Nobody had thought of taking off when the temperature was 120-some degrees.”

American Airlines told ABC15 that all the performance charts for large jets have long-since been updated for higher temperatures and the airline has no worries about delays for those scheduled flights. However, not all small regional aircraft have updated charts.

“If the temperatures rise to the extent that it would inhibit our calculations of weight and thrust for ‘lift’ accurately, then we cannot take off, so we may proactively delay some departures until the air temperature reduces,” said John Daley, American Airlines managing director at Phoenix Sky Harbor, in an email.

Tilmon said airplanes will still fly in extreme heat, but to do so without accurate data is not only unsafe – it’s illegal.

“You didn't want to pretend you had the right numbers and you didn't. That's called guesswork and that's called an accident...and yes, illegal,” said Tilmon.

Tilmon has a cautionary tale from many years ago when the airline industry wasn't quite as careful calculating hot weather. A discrepancy between the temperature at the tower and the temperature on the runway caused him a dicey takeoff on a hot day in Tucson.

“I'm looking down at the end of the runway and it was coming up pretty damn fast,” said Tilmon, adding that his flight crew had to turn off the air conditioning system mid-runway to find the extra power needed to get the wheels off the ground. “It was said that we made a rooster tail across the desert that we were so low.”

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