Question: Do airplanes have a hard time taking off in Arizona because of the hot weather?
— Submitted by reader Chris Batten, Lilburn, Ga.
Answer: 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 ABQ because of altitude and temperature?
— Rodger B., Albuquerque
A: Airports such as ABQ 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. An airplane that may climb well at sea level on a cool day may not be able to take off on a hot day in ABQ.
Q: Does a hot day in Denver require a greater air speed for rotation?
— John Fuller, Racine, Wis.
A: Yes, the indicated airspeed is the same, but the true airspeed is higher. True airspeed is the indicated airspeed corrected for non-standard density (altitude and temperature). The groundspeed of the airplane at rotation would be higher at Denver or Mexico City than at Washington or New York because of the higher true airspeed.
Q: I had heard that over 117 degrees Fahrenheit, planes cannot fly. Is there a specific temperature at which they can’t operate?
— Joyce Gioia
A: There are two parts to your question.
When an operator purchases an airplane, the manufacturer provides performance charts for normal operations. These charts have upper limits and are generally around the figure you cite (near 120F). 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 from the manufacturer, 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. The actual values can vary from manufacturer to manufacturer slightly.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
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