Accident Overview
On 20 August 1989, two pilots, one acting as passenger, departed Sion airport in a Maule M-5-210 TC (HB-EZK) for a pleasure flight with the intention of landing on the Monte Rosa glacier. The aircraft was equipped with a turbocharged engine and skis for glacier operations. After a first successful touch-and-go landing, the responsible pilot decided to land again and come to a stop. During the second landing, the aircraft began sliding sideways. The pilot attempted a go-around by applying full throttle, but the engine did not provide sufficient power. The aircraft fell into a crevasse and was destroyed. Both pilots sustained serious injuries.
Flight History
Prior to the accident, the aircraft had been modified with a metal housing between the air filter and cowling to prevent snow ingestion into the turbocharger intake, but this modification was not documented in technical records nor reported to the civil aviation authority. The pilot on the left seat (Pilot Y) was unfamiliar with the Monte Rosa glacier and had expressed concerns about turbocharger lag. Pilot X, on the right seat, was a glacier flight instructor. During the flight, Pilot Y initially handled the controls but hesitated due to lack of confidence in the turbocharger. After three overflights, they executed the first landing and immediate takeoff. On the second approach, Pilot X intended to stop but the aircraft slid leftwards. He initiated a go-around and moved the throttle lever rapidly back and forth according to Pilot Y. The power increase was slow, and the aircraft could not climb, falling into a crevasse.
Cause and Contributing Factors
The accident was due to inadequate handling of the engine controls. Contributing factors were:
- Weak compression pressure in two cylinders of the engine.
- High density altitude at the accident site (elevation 4100 m).
Damage and Injuries
The aircraft was destroyed upon impact with the crevasse. Both pilots suffered serious spinal injuries from the relatively flat impact. The left wing was broken off; engine power at impact was low as indicated by propeller blade deformation. No fire occurred. The pilots were rescued by helicopter after an emergency locator transmitter and a handheld radio transmission were detected by another aircraft.