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Training and Safety Tip: Empty a seat for high heat

High elevation, high temperatures equal high density altitude

“The airplane is below the published gross weight limit. Why does your rental policy limit the airplane to three people?” That is a summertime policy at several flight schools in the high and hot regions of the western United States. Asking the question unfortunately illustrates a misunderstanding or lack of knowledge that can be fatal.

Nobody was hurt when this Piper Arrow was significantly damaged during a runway excursion, though the aircraft was eventually returned to service. Photo by Ed Helmick.

On a hot day, the issue is not about gross weight limitations, it’s about the degradation of performance due to density attitude. Utah’s Provo Municipal Airport has a field elevation of 4,497 feet mean sea level (msl). On an August day, the density altitude can be close to 9,000 feet msl. Small airplanes typically have a published service ceiling of 12,500 feet to 15,700 feet msl and most pilot’s operating handbooks do not provide takeoff calculations at a pressure altitude above 8,000 feet. (Service ceiling is defined as the altitude at which the airplane’s climb rate is equal to or less than 100 feet per minute at gross weight with a new engine.)

But takeoff performance is not the only concern: Pay attention to terrain and environment, and factor in the need to clear hills and mountain ridges, fly out of mountain valleys, and be prepared for attention-getting downdrafts. Also remember that if a landing does not go according to plan, a go-around with gear and flaps extended over the runway and climb performance compromised by high density altitude can become challenging. The lesson: During the summer heat, when performance is decreased by density altitude, compensate by flying with less weight.

A few years ago, despite the airplane rental company’s policy that limited occupancy to three people in a four-seat Piper Arrow, a renter pilot put a fourth person in the airplane that was fully loaded with fuel. It is doubtful the pilot did a weight and balance calculation, and the airplane was probably over its allowable gross weight with an aft center of gravity. After a short flight, the pilot returned to the airport and initiated a go-around after a ballooned landing. The airplane stalled in the go-around effort, resulting in a hard landing, and it careened off the edge of the runway. Crossing a ditch, the main gear was torn off and the aft fuselage was heavily damaged. Fortunately, no one was injured. The near catastrophe could have been avoided if the airplane had been flown at a lighter weight. This example just reinforces the need to educate pilots about the reality of density altitude.

Ed Helmick

Ed Helmick has been a flight instructor since 1988. He formerly managed a flight school in Spanish Fork, Utah, as well as schools in Scottsdale, Arizona; and Honolulu, Hawaii.
Topics: Training and Safety, Aeronautical Decision Making, Technique
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