What happened
On November 11, 2021, a Piper PA4/6R-350T, registration ES-FLG, departed Hyvinkää Airport (EFHV) for Tallinn Airport (EETN). The flight was being conducted under Instrument Flight Rules (IFR) with a planned diversion to Kärdla Airport (EEKA) in the event of necessity.
Approximately 23 minutes into the flight, the pilot noticed fluctuations in the engine's intake manifold pressure. Shortly thereafter, the aircraft's onboard systems issued low fuel warnings for the right tank, followed by a "BOOST PUMP FAIL" message. As the aircraft approached Tallinn, the engine performance became increasingly irregular. To prevent a complete engine shutdown, the pilot elected to use the propeller in flight idle mode. At 16:06 local time, the aircraft landed on an asphalt area adjacent to the end of runway 26. There were no injuries and no significant damage to the aircraft.
The investigation
The Estonian Safety Investigation Bureau (OJK) examined the aircraft's fuel system, including flight data from the Garmin G1000, cockpit voice recordings, and air traffic control communications. Investigators performed a physical inspection of the fuel tanks, finding only approximately 600 ml in the left tank and 500 ml in the right tank.
The investigation scrutinized the pilot's flight planning and previous flight logs from the preceding week. It was noted that while the pilot relied on onboard computer readings for fuel quantity, the aircraft's fuel level sensors were found to be stuck in a fixed position following the incident. Furthermore, the investigation compared the pilot's calculated fuel consumption against actual usage, noting that the aircraft consumed more fuel per hour than the pilot had estimated during planning.
Findings
- The pilot underestimated the required fuel quantity for the flight, failing to account for the actual fuel burn rate and specific engine operating modes.
- The pilot relied solely on the onboard computer's fuel readings rather than verifying the actual fuel levels via physical inspection of the tank filler caps.
- The pilot proceeded with the flight despite knowing that the remaining fuel might be insufficient to reach the intended diversion airport.
- The pilot failed to respond to multiple "Master Warning" and "Master Caution" alerts regarding low fuel levels.
- The pilot did not declare an emergency or notify air traffic control of the developing situation, maintaining standard communications until the landing.
- The engine shutdown was caused by fuel exhaustion.
- The aircraft's fuel level sensors were found to be stuck in a non-responsive position following the event.