What happened
On May 1, 2024, a Piper PA-31-310, registration LN-NAB, was conducting a specialized three-dimensional laser scanning mission east of Stockholm. The flight, operated as a specialized operation, was intended to take off from and return to Stockholm/Västerås Airport. During the return leg of the mission, the aircraft experienced a total loss of power. The right engine failed first, followed three minutes later by the failure of the second engine while the aircraft was at an altitude of approximately 1,801 feet.
Unable to reach the runway, the crew executed an emergency landing in a field located roughly 3.6 nautical miles from the airport. During the landing roll, the aircraft tipped, resulting in structural damage to the left wing spar and wing tip. There were no injuries to the three occupants on board.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft, the accident site, and various technical records. The investigation focused on the aircraft's fuel systems, the operator's flight planning, and the accuracy of the cockpit instrumentation. Investigators analyzed fuel consumption logs, flight data, and the aircraft's mass and balance configuration. The inquiry also reviewed the operator's Safety Management System (SMS) and how risks related to fuel management were documented and mitigated.
Findings
Several interconnected factors led to the dual engine failure. The primary cause was fuel exhaustion, driven by a combination of inaccurate instrumentation and inadequate planning. The investigation established that the fuel gauges provided unreliable, higher-than-actual readings, meaning the crew believed they had significantly more fuel than remained in the tanks.
Furthermore, the actual fuel consumption during the mission was higher than the pilots had planned. While the crew estimated a consumption of 110 liters per hour, the actual rate was approximately 133 liters per hour. This discrepancy was exacerbated by the nature of the mission, which required constant power adjustments, and the fact that a cockpit navigation screen obscured critical engine instruments, making it difficult to optimize engine leaning. Additionally, the operator's safety management processes failed to adequately address the specific risks of this operation, such as the lack of precise fuel consumption data and the need for regular gauge calibration.