What happened
On July 30, 2019, a privately operated Piper PA-16 Clipper, registration N5723H, was conducting a VFR flight from Luzern-Beromünster to the same destination. During the cruise phase, while flying near the Jura mountains at approximately 4,300 ft AMSL, the aircraft encountered significant turbulence due to prevailing north winds. While the pilot was operating the engine using the right wing tank, the engine suffered a sudden loss of power near Weissenstein.
The pilot immediately attempted to troubleshoot the failure by switching to the left tank, adjusting the mixture to full rich, and applying carburetor heat. However, the propeller failed to windmill. The pilot then identified a suitable landing field near Welschenrohr and initiated an emergency descent. During the approach, the pilot manually activated the Emergency Locator Transmitter (ELT) and issued a Mayday call on the Grenchen frequency. During the extended final approach, the pilot used the starter, which successfully restarted the engine. After confirming normal engine operation, the pilot climbed away and continued to the original destination, landing safely at Luzern-Beromünster.
The investigation
The investigation focused on the fuel system configuration and the circumstances leading to the power loss. The aircraft's fuel system had been modified via a Supplemental Type Certificate (STC) to include an auxiliary tank in the right wing. This modification carries specific operational limitations: the aircraft must be flown in straight and level flight when using the right tank to ensure consistent fuel flow. The investigation also examined the pilot's emergency response and the impact of the ELT's audible alarm during the procedure.
Findings
- The engine failure was caused by interrupted fuel flow from the right wing tank due to turbulence.
- The aircraft was operating on the right tank, which is subject to limitations requiring straight and level flight to maintain adequate fuel pressure.
- The amount of fuel in the right tank was below 30 liters, a level where fuel delivery issues are known to occur during maneuvers.
- The pilot's decision to select a landing field and activate the ELT was considered safety-conscious, although the loud cockpit alarm from the ELT was noted as a distraction.
- The pilot did not immediately notify all relevant authorities of the resolution, which led to a period of uncertainty and the maintenance of an emergency status at Grenchen airport.