Flight Details
The accident airplane, a wheel/ski equipped aircraft, departed on a U.S. Government flight for the Department of Interior, National Parks Service, carrying three park rangers. The flight was operated as a VFR, on-demand air taxi flight to the Denali National Park base camp, located at 7,200 feet msl on the Kahiltna glacier. The base camp was the intended destination for the rangers to begin mountain patrol operations on Mt. McKinley, Alaska.
Weather Conditions and Communications
Variable weather conditions with low ceilings near the base camp made landing problematic throughout the day. Prior to departure, the pilot opened a VFR flight plan and was advised that an AIRMET for mountain obscuration and turbulence was current for the area. About 45 minutes after departure, the pilot communicated via radio with another pilot at the Kahiltna base camp, who reported that the upper portion of the glacier was closed due to low clouds. The accident pilot responded that the lower portion of the glacier was closed by weather and that he was diverting toward the west, toward another glacier drainage. A ranger onboard then contacted the ranger station using a hand-held radio, stating that the flight was returning.
Accident Sequence
The accident airplane did not return to its base and was reported overdue. The wreckage was located the following day, scattered over an area of about half a mile. Evidence indicated that the airplane broke apart in-flight. The left wing, left wing lift strut, left landing gear strut, left door, and windshield were found on the upper portion of a steep hillside. The engine struck the ground below the left wing, separating the propeller, and then tumbled downhill. The fuselage came to rest about a quarter mile below the left wing and was consumed by a postcrash fire.
Wreckage Examination Findings
Examination of the wreckage revealed that the wing spars and each horizontal stabilizer exhibited all negative bending signatures. The flap handle was found extended to 20 degrees. The airplane manufacturer does not publish any negative structural load factors for a flaps down configuration.
Meteorological Analysis
A review of meteorological data revealed an occluded front with convective activity that progressed northward toward the accident area, accompanied by heavy rain and hail. The front was positioned near the accident area at the time the airplane was diverting away from the mountain.
Operator Information
The pilot was the chief pilot for the operator. The director of operations for the company had the responsibility of operational control for the operator.