Air Safety Institute Safety Spotlight
The warm days of summer beckon many pilots skyward, but with warmth comes the performance-robbing effect of high density altitude. Over mountainous terrain - with the hobbled airplane surrounded by 14,000-foot peaks - the effects of high density altitude can quickly turn tragic.
On August 7, 2006, the pilot of a Piper PA-28R-201 Arrow was returning to California from Oshkosh, Wisconsin. While attempting to navigate through mountainous terrain northwest of Salida, Colorado, the pilot 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.
They had stopped overnight at Harriet Alexander Field (elevation 7,523 feet) in Salida. As they prepared to depart the following morning, the density altitude was about 9,400 feet 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 wanted to fly west across Monarch Pass (elevation 11,312 feet) to Utah. 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 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 another route, running northwest for about 10 miles before dead-ending near the box canyon's terminus.
Several witnesses saw an airplane flying northwest up the canyon. When it failed to fly back out, a witness discovered the wreckage and the lone survivor.
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. And to a pilot unfamiliar with the terrain, the mouth of one canyon can look very much like another. For more information, check out the AOPA Air Safety Foundation's Mountain Flying online course.
An aviation technical writer for the AOPA Air Safety Foundation, Carl Peterson creates interactive courses and other safety education materials for the aviation community. He has been flying since 1989.
By Carl Peterson