What happened
At approximately 1s30 Central Daylight Time, an Aero Commander 500S, registration N5800H, departed runway 31 at the Rankin Inlet Airport in Nunavut. The aircraft, which was at its maximum takeoff weight, was being flown by two experienced pilots and one passenger as part of a delivery flight from the United States to Switzerland.
Shortly after rotation, the cylinder head temperatures on both Lycoming TIO-540-E1B5 engines began to rise, and both engines experienced a loss of power. Although the crew had previously aborted a takeoff attempt due to similar power issues, a second attempt resulted in the same engine failure. Unable to maintain altitude, the pilots extended the landing gear and performed a forced landing on a flat area approximately 1500 feet southwest of the runway 13 threshold. There were no injuries, though the aircraft sustained substantial damage.
The investigation
The investigation focused on the fuel source and the engine failure sequence. It was discovered that the aircraft had been refueled using two 45-gallon drums. While the first drum contained the correct 100LL AVGAS, the second drum contained contaminated "slops." The investigation found that the fuel handler had mistakenly delivered the drum of slops because it was placed near the fresh stock of 100LL AVGAS and featured similar markings.
Because the aircraft's fuel system design allows fuel from the wing cells to flow into a central cell, the contaminated fuel from the second drum was distributed to both engines. During the initial takeoff attempt and subsequent run-up, the engines were operated at lower power settings, which prevented the detection of the issue. However, the higher power settings used during the second takeoff caused the contaminated fuel to detonate, leading to the loss of power.
Findings
- The fuel handler selected the drum of slops in error because it was located near the sealed stock of 100LL AVGAS.
- The contaminated drum had markings similar to the correct fuel, making it difficult to identify.
- The fuel handler failed to notice that the large bung plug on the second drum was unsealed.
- The pilots, who were inexperienced in refueling from 45-gallon drums, did not verify the fuel grade in the second drum.
- The use of contaminated fuel caused both engines to lose power due to detonation at high temperatures.
- The aircraft's fuel system design allowed the contaminated fuel to reach both engines via the central fuel cell.