What happened
On 25 July 2010, a PA 31-310 Navajo, registration N80HF, was conducting a private flight from Antwerp Airport to North Weald Aerodrome. After completing customs in Belgium, the pilot departed for the return leg of the journey. During the flight, the aircraft climbed to FL50 before descending across the English Channel toward Essex.
As the aircraft approached North Weald, the pilot noticed the right engine's manifold pressure and propeller RPM began to fluctuate, accompanied by a surging noise. After switching the fuel selector to the outboard tank, the right engine failed. Shortly thereafter, the left engine experienced similar fluctuations and subsequently ran down. The pilot feathered both propellers and prepared for an emergency landing on the paved runway surface, opting to keep the landing gear retracted to maintain a level attitude for touchdown.
The aircraft touched down at 1521 hrs, decelerating rapidly in the middle of the runway. The landing resulted in severe damage to the fuselage skin and frames, as well as damage to the propeller tips. There were no injuries to the pilot or the four passengers on board.
The investigation
The AAIB examined the aircraft's fuel system and the pilot's planning. Post-accident testing of the fuel tanks revealed that the inboard tanks contained very little fuel, while the outboard tanks were empty. No external leaks were found, and the fuel filters showed no signs of contamination.
The investigation also reviewed the pilot's fuel calculations. The pilot had relied on an Information Manual that provided fuel consumption figures for specific power settings. However, the pilot's technique involved leaning the engines to peak EGT and then slightly enriching the mixture, a practice that can increase fuel flow beyond the manual's stated figures. Additionally, the investigation noted that the pilot had no reliable way to verify the exact amount of fuel onboard, as the aircraft lacked a method for dipping the tanks and the fuel gauges were not entirely reliable.
Findings
- The aircraft experienced fuel exhaustion.
- The loss of power was caused by a combination of factors, including a potential discrepancy in the actual fuel loaded at departure and a higher fuel consumption rate than the pilot had calculated.
- The pilot's engine-leaning technique likely increased the actual fuel flow above the figures provided in the manufacturer's Information Manual.
- The lack of a reliable method to verify fuel quantity via tank dipping or accurate gauges contributed to the error in fuel planning.