Accident Analysis: Yeah, it’s the heat

Hot air, on the other hand, saps performance faster than many pilots realize. On a July day, Death Valley’s Furnace Creek Airport, located 210 feet below sea level, can have a density altitude higher than that at Denver International Airport on a particularly cold morning in January. The difference in actual elevation is more than a mile. Outside the desert Southwest high humidity can add a few more hundred feet, but the principal culprit is temperature.

Pilots facing unfamiliar high density altitudes need to make as much as possible work in their favor, starting with double-checking performance calculations they may no longer routinely make. Unfavorable results aren’t an invitation to try anyway and see what happens. Even when it appears feasible, it’s best to maximize the margin for error. The Cessna 210 that crashed during an attempted departure from Burley, Idaho, in 2011 was turbocharged, so at least its engine could produce its full 300 horsepower.

But the pilot not only chose to load the airplane within 50 pounds of maximum gross weight and take off from 4,150 feet at 2:30 on an August afternoon—he did it downwind. With a six-knot tailwind at the density altitude of 7,116 feet, 4,048 feet would have been needed to clear a 50-foot obstacle with perfect technique—44 feet less than the actual runway length. This pilot’s base was on the Southern California coast at about 700 feet mean sea level.

If pushing the limits of calculated performance seems unwise, how about taking off when those calculations can’t even be performed? In June 2010, the owner of a Piper Lance tried to depart from an Arizona airport in conditions that were literally off the charts—beyond the range of temperatures and pressure altitudes covered by the takeoff performance charts in the pilot’s operating handbook. (To be fair, the effective crosswind was also 25 to 32 knots, gusting close to twice the airplane’s demonstrated crosswind component.) The POH warns that “extrapolation beyond the limits on the charts should not be used for flight planning purposes.” The Lance crashed into a nearby high school and ignited a fire requiring 10 to 12 hours to extinguish—in part because it detonated “an unknown amount of gun ammunition” aboard the aircraft. Give the pilot credit, at least, for doing nothing halfway.

Those who’d prefer not going out in a blaze of glory—or something—might adapt the motto from This Old House to read, “Compute twice, add 50 percent—and take off once if the numbers work.” Otherwise wait, lighten the load, or both.

David Jack Kenny is an aviation writer and statistician.