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Density altitude sacks lost pilotDensity altitude sacks lost pilot

DEN06FA111 DEN06FA111 

The warm days of summer beckon many pilots skyward, but with that warmth comes the performance-robbing effect of high density altitude. As temperatures rise, air density drops, which means fewer air molecules are flowing over airfoils and propellers or combusting inside engines. This summertime trifecta of lost lift, reduced propeller efficiency, and sagging horsepower is challenging enough in the flatlands. Over mountainous terrain—with the hobbled airplane surrounded by 14,000-foot peaks—the effects of high density altitude can quickly turn tragic.

On Aug. 7, 2006, the pilot of a Piper PA-28R-201 Arrow was returning to California after attending EAA AirVenture in Oshkosh, Wis. While attempting to navigate through mountainous terrain northwest of Salida, Colo., the pilot made a wrong turn and flew into a box canyon. Unable to outclimb the terrain, the aircraft struck a stand of pine trees and came to rest inverted. The crash killed the 4,400-hour airline transport pilot and seriously injured his passenger.

Making their way west from Oshkosh, the San Jose-based pilot and his passenger had arrived at Harriet Alexander Field (elevation 7,523 feet msl) in Salida around 8 p.m. on the day before the accident. The following morning, the pilot used his laptop computer to obtain a DUATS weather briefing and file a VFR flight plan to Milford, Utah. The density altitude in Salida that morning was about 9,400 msl, meaning aircraft flying in the area would perform as though they were about 2,000 feet higher than their actual altitude.

According to the airport manager, the pilot asked which route he should take to Utah. The pilot wanted to fly west across Monarch Pass (elevation 11,312 feet msl). The manager suggested that he instead fly south through the lower-elevation Poncha Pass before turning west. The pilot ignored the advice. The airplane took off around 10 a.m. and turned toward Monarch Pass.

The Arrow flew west along U.S. Highway 50, which eventually runs through Monarch Pass toward Utah. Over the town of Maysville, however, the pilot began following County Road 240, which runs northwest through a box canyon for about 10 miles before dead-ending near the canyon’s terminus.

Several witnesses saw a low-wing, single-engine airplane flying northwest up the canyon. One witness, located about two miles from the accident site, went to investigate when the aircraft failed to fly back out. He discovered the wreckage and the lone survivor sitting on a rock nearby. The injured passenger had no memory of the events leading to the accident.

The Arrow crashed at 10:20 a.m. at an elevation of about 12,000 feet msl. Terrain surrounding the accident site quickly rises to between 13,000 and 14,000 feet msl. The aircraft’s throttle was found in the full-forward position. The vertical speed indicator showed a climb rate of 130 fpm. NTSB investigators estimated the Arrow’s groundspeed at the time of the crash was 59 knots.

The board concluded that inadequate preflight planning and preparation caused the accident. Contributing factors were the pilot’s lack of familiarity with the geographical area, his becoming lost and disoriented, his decision to disregard the advice of local pilots, and the high density altitude, which reduced the airplane’s climb performance.

This accident illustrates the unique hazards of mountain flying. Summer temperatures can push the density altitude to heights that approach or exceed a light aircraft’s service ceiling, despite what the altimeter might be reading. Moreover, to a pilot unfamiliar with the terrain, the mouth of one canyon can look very much like another. Is it a mountain pass leading to the relative safety of lowlands beyond—or a dead end? Like the proverbial blind choice between the lady and the tiger, picking the wrong door can end very, very badly.

Don’t let high density altitude
take you by surprise

Summer’s warm temperatures and increased humidity can turn almost any flight into a high-density-altitude challenge. Add to that high terrain or a heavily loaded airplane and the likelihood of an accident greatly increases.

Of course, high density altitude isn’t only a concern on takeoff. You need to keep the effects of decreased aircraft performance in mind throughout every phase of flight—and leave yourself an extra margin of safety in the event of an emergency.

AOPA and the AOPA Air Safety Foundation offer a wide array of resources to help you prepare for just about any high-density-altitude situation. Get an overview of the subject with the density altitude subject report from the AOPA Pilot Information Center. You can also delve deeper with the interactive Mountain Flying online course.

Finally, get a personal perspective, or share your thoughts, on the Safety eJournal blog entry “Summertime and the crashing is easy.” Still have questions? Contact the experts in the AOPA Pilot Information Center at 800/USA-AOPA.