What happened
On November 2, 1962, a Piper J3C (registration HB-OCO) was conducting a private VFR flight from Altenrhein to Innsbruck. While flying over the Arlberg region, the crew experienced significant engine power fluctuations and vibrations in the tail section. In an attempt to stabilize the engine, the pilots reduced power and trimmed the aircraft in a tail-heavy configuration, which temporarily stabilized the vibrations but resulted in a continuous descent.
As the aircraft approached the St. Anton area, the engine power dropped further, making it impossible to maintain altitude. Due to fog in the direction of Innsbruck, the pilots sought an alternative landing site near Pettneu. Finding no suitable fields due to the presence of high-voltage power lines, the crew attempted a low-altitude landing on a sloping meadow. During the final approach, the aircraft lost altitude and struck the ground at a steep angle, resulting in two severe injuries to the crew.
The investigation
An investigation into the accident examined the mechanical state of the engine and the flight path. Technical analysis of the fuel system revealed that the connection nipple was approximately two-thirds obstructed by debris, including internal paint flakes and various dirt particles. This obstruction caused an inconsistent fuel flow, which directly led to the observed RPM fluctuations and engine instability.
Investigators also analyzed the aircraft's configuration during the landing. The tail-heavy trim was determined to be a deliberate attempt by the pilots to eliminate tail vibrations caused by the irregular engine running. The investigation also noted that the landing site was constrained by nearby high-voltage lines, which limited the available approach paths.
Findings
- The primary cause of the engine malfunction was a fuel supply restriction caused by the accumulation of paint chips and dirt within the connection nipple.
- The engine's irregular running caused vibrations in the tail section, which the pilots attempted to mitigate through extreme trim adjustments.
- The decision to perform an emergency landing was appropriate given the inability to maintain altitude and the risk of total engine failure.
- The severity of the impact was exacerbated by the difficult terrain and the presence of high-voltage power lines, which prevented a more favorable approach.
- The pilots attempted to perform a controlled landing on the wheels rather than a belly landing, which, while intended to protect the aircraft, resulted in higher impact forces for the occupants.