Extreme heat can hinder flights

Q: Do airplanes have a hard time taking off in Arizona because of the hot weather?

— Chris Batten, Lilburn, Ga.

A: I would not say they have a hard time, but performance is definitely limited by the heat. Hot air does not allow the wing to create as much lift (fewer air molecules); therefore, the weight must be reduced to maintain the required climb path. Very high temperatures such as Arizona, the Middle East or other desert environments require careful preflight planning.

Q: What kind of challenges do pilots face when taking off in the summertime from Albuquerque because of altitude and temperature?

— Rodger B., Albuquerque

A: Airports such as Albuquerque that are at high altitude have less air with which to produce lift. The atmospheric pressure decreases with altitude. When it is hot, air is less dense than when it is cold. Adding the two issues together means a high-altitude airport on a hot day has less dense air at lower pressure. Pilots calculate this to determine the density altitude.

Q: I had heard that over 117 degrees F, planes cannot fly. Is there a specific temperature at which they can’t operate?

— Joyce Gioia

A: The airplane manufacturer provides performance charts for normal operations. These charts have upper limits and are generally around the figure you cite (near 120 F). If the temperature exceeds the upper value on the chart, then it is not possible to perform the required calculations, and the airplane is not legally allowed to fly. An operator can purchase high-temperature performance charts, which enable more precise calculations that may allow the airplane to depart. There is a temperature at which all performance charts stop, making it impossible to fly.