What happened
On January 6, 2016, a SA226-TC operated by a Spanish company departed Paderborn-Lippstadt Airport, Germany, bound for Girona, Spain. The flight was being conducted without passengers or cargo. During the flight, the crew identified a significant fuel imbalance between the left and right wing tanks. The imbalance was so severe that the pilot had to apply maximum trim to maintain control.
Due to the developing situation, the crew decided to perform an unscheduled landing at Saarbrücken Airport. Prior to arrival, the tower was notified of a fuel leak. During the approach, the pilot reported that the aircraft had become increasingly difficult to maneuver. Upon landing on runway 27, the aircraft was met by airport fire services. After the aircraft came to a stop, smoke was observed emanating from the right engine, and flames were reported to have emerged from the engine area. Firefighters utilized foam and CO2 to extinguish the fire. There were no injuries to the crew.
The investigation
The BFU examined the aircraft and found that a fuel line connecting the fuel heater to the fuel pump assembly on the right engine had ruptured. The investigation revealed that the two fuel lines at the fuel heater had been incorrectly installed, with their connections swapped. Furthermore, the lines were not properly secured with safety lacquer, and the failed line was found to have been installed under tension.
Microscopic analysis of the fracture surface indicated that the failure originated from fatigue cracking caused by surface irregularities (grooves) on the line, which eventually led to a complete structural failure. The investigation also determined that the fuel imbalance reached approximately 1,028 lbs, which was roughly double the maximum demonstrated imbalance permitted by the manufacturer.
Findings
- The primary cause of the incident was the rupture of a fuel line on the right engine, which created a massive fuel imbalance.
- The fuel line had been improperly installed, leading to excessive structural stress.
- The crew was unable to isolate the leak or implement fuel balancing procedures because no standard operating procedure existed for handling a fuel leak in this aircraft type.
- The fuel imbalance reached levels that placed the aircraft outside its safe demonstrated operating envelope, resulting in the reported control difficulties.