What happened
On February 23, 1967, a Piaggio P-166, registration D-IHAK, was performing a return flight from Albenga, Italy, to Munich, Germany, following a periodic maintenance check at the manufacturer's facility. The aircraft was operating under instrument flight rules (IFR) across the Swiss Alps.
At approximately 16:44, the pilot contacted Zurich Radar after passing the Monte Ceneri NDB, reporting that the aircraft was unable to maintain its assigned flight level of 160 due to engine trouble and a loss of altitude. The aircraft was experiencing moderate icing. Radar controllers attempted to direct the aircraft away from the highest peaks by instructing a course change toward the Reus Valley. Despite the pilot's efforts to maintain flight level 120, the aircraft disappeared from radar screens at 17:06, shortly after confirming a new heading.
Search efforts initiated that evening located the wreckage the following day on the southern slope of Piz Acletta at an altitude of approximately 2,500 meters. The two occupants, both employees of the aircraft's operator, died in the crash.
The investigation
The investigation examined the wreckage, which was found embedded in a steep snowdrift. The aircraft had struck the terrain in an uncontrolled attitude. Post-crash analysis of the engines revealed that the pilot had shut down the right engine and placed its propeller in the feathered position. The left engine's throttle was at full power, while the right engine's fuel mixture was at cut-off.
Investigators also reviewed weather data, noting that a cold front was moving through the region, bringing heavy snow, strong winds, and significant turbulence. The pilot had consulted weather reports in Albenga prior to departure, which likely influenced the decision to fly the more eastern route over the Alps to attempt to clear the mountains before the front's arrival.
Findings
- The pilot had successfully shut down the right engine and feathered the propeller following an unspecified engine malfunction.
- Moderate icing likely caused the engine performance degradation that necessitated the engine shutdown.
- The aircraft was flying in highly unstable air masses characterized by strong, localized turbulence and heavy snow.
- Due to the loss of one engine, the aircraft lacked the necessary power reserve to maintain the required safety altitude.
- It is highly probable that the aircraft entered a stall while maneuvering through turbulent air, leading to an uncontrolled descent and impact.