June 10, 2009
Density altitude is something all pilots learn during flight training, but it’s likely not something you account for year-round. As the temperature creeps up during the summer months, don’t overlook density altitude’s effect on your aircraft’s performance. If not anticipated, its effects on a flight can be perplexing and detrimental; it can even cause accidents.
You may remember what your instructor told you: “Density altitude is pressure altitude corrected for nonstandard temperature.” Simply put, density altitude is the altitude at which the aircraft feels it is flying. A high density altitude means that the air is less dense than normal, so your aircraft will perform as if you were flying at a higher altitude. On a hot, humid day, the aircraft will accelerate and climb more slowly and will need to move faster to attain the same amount of lift.
To minimize the risks of a high density altitude, fly in the morning or evening when the temperature is cooler, and don’t fill the tanks to the brim. A good rule of thumb is to abort your takeoff if you do not have 80 percent of your takeoff speed halfway down the runway. Before flying to a high-elevation airport, know whether your aircraft climbs more efficiently with the first increment of flaps.
More tips for summer flying are available in AOPA’s revised subject report on Density Altitude and the AOPA Air Safety Foundation’s Summer Weather Safety Hot Spot.
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