ERA12LA165 · Piper PA-31-310

On the morning of the accident, the pilot had the airplane topped off with 22 gallons of fuel, which he visually confirmed. The pilot flew the airplane to an offshore island that did not have fuel, deplaned passengers, and was returning to the mainland. The pilot planned for 4.6 hours of round trip operation and had previously flown similar flights to the same destination with durations of 4.6 to 5.1 hours. The outbound leg was completed without any anomalies noted; the pilot reported that the preflight inspection, start, taxi, runup and takeoff checks for the returning accident flight were "normal." Throughout the climb after takeoff, the pilot noted less manifold pressure on the left engine, and, by the time the airplane reached a cruising altitude of 10,500 feet, the engine was unable to maintain more than 55 percent power at 2,200 rpm and 26 inches of manifold pressure. The pilot matched the right engine power setting to the left and switched from the main fuel tanks to the outboard tanks at the top of the climb.

He consulted the pilot operating handbook, which indicated a 4 gallon-per-hour reduction in fuel consumption at that power setting. En route, the left outboard tank emptied about 15 minutes before the right tank, which the pilot later reported was unusual because both engines normally burned evenly. About 60 nautical miles (nm) from the destination, the pilot initiated a descent, and about 55 nm from the destination, the left engine began surging. According to the pilot, the fuel gauges at the time indicated just below 1/4 full on the left main fuel tank and above 1/4 full on the right main fuel tank. The pilot turned on the emergency boost pump and selected fuel crossflow, which restored power to the left engine.

The pilot then turned the airplane toward the nearest mainland airport, about 32 nm away, and contacted approach control. Shortly thereafter, the left engine surged, then lost power, followed closely by the right engine. The pilot turned on the emergency boost pumps, switched to the outboard and inboard fuel tanks sequentially (separately and with cross flow) but was unable to restore engine power. With the airplane descending through about 7,500 feet, the pilot completed the feathering procedure for both engines and established a best glide attitude, eventually landing the airplane on a beach.

On-scene examination of the airplane did not reveal the presence of fuel, and no evidence of fuel leakage. The investigation did not reveal any mechanical malfunctions or failures that would have precluded normal operation, and the pilot did not note any preexisting anomalies with the fuel quantity indicators. Insufficient and contradictory information precluded a determination as to why the airplane ran out of fuel. The pilot had previously flown the same route with ample fuel remaining, but couldn't for this flight. The left engine would not produce normal power, so the pilot reduced right engine power, which should have resulted in more en route flight time, but didn't. Lower power settings should have resulted in a longer time to destination, yet based on provided flight times, it didn't. The left outboard fuel tank ran out of fuel sooner than normal, indicating that either the left engine was utilizing an excessive amount of fuel, or the fuel tank had not been filled completely or fuel was drained from it at the intermediate stop. Also, when the left engine stopped the first time, the fuel gauge, which had not been previously been noted as inaccurate, reportedly still indicated the presence of fuel at just under 1/4 tank.

A direct line plot from the departure airport for the accident flight to the intended destination indicated the airplane overflew an island airport with fuel facilities about 105 nm from the destination and about 50 nm before the left engine began to surge. It is unknown if the pilot had sufficient information at that point to properly judge whether he should bypass an available en route fuel stop. However, with the information he did have, he judged that he had adequate fuel to complete his flight, which ultimately proved to be incorrect.

Verbatim NTSB analysis and probable cause from the NTSB dataset