Incident
On 20 April 2023, a Piper PA-28-181 'Archer' aircraft, registered VH-FEY, departed Carnarvon, Western Australia for a private flight with the owner-pilot and two passengers on board. The aircraft initially proceeded to Geraldton to drop off one passenger before continuing to Jandakot (Perth). The pilot considered there was sufficient fuel remaining for the return journey and did not refuel at Geraldton. After cruising at 5,500 ft, the pilot descended due to airspace restrictions. About 10 km north of Fremantle, while tracking coastal over water, engine power subsided to idle over a couple of seconds then recovered to cruise power. The pilot selected mixture to full RICH and carburettor heat to ON. The engine power subsided and recovered several times over about two minutes. There were no indications of mechanical failure. Unable to maintain height, the pilot turned for a forced landing on the beach but saw people there, so decided to ditch in the ocean. The aircraft contacted the water, skipped, then the right wing dropped and dug in, stopping the aircraft. The pilot and passenger exited uninjured and swam to shore.
ATSB Findings
The pilot departed Carnarvon with sufficient fuel for the intended flight but did not carry out regular fuel quantity checks or keep a written fuel log. During cruise at 1,900 ft, engine power subsided to low power then returned to normal, occurring several times, probably because of a lack of usable fuel in the selected (right) tank. The pilot responded with some emergency procedures but did not select the other (left) tank, which contained usable fuel. Engine power was not restored, leading to the ditching. Prior to departure from Geraldton, the pilot drained significant water from both fuel tanks and the fuel strainer, but no evidence of fuel contamination was found. The engine had been in service for 28 years since overhaul and 13 years since a bulk strip, more than double the recommended 12-year interval, but no engine defects were identified, and the maintenance was carried out, so this was not a factor.
Fuel Management
The pilot did not compile a flight or fuel plan for the return journey. The expected fuel remaining was based on experience rather than progressive recording. The pilot's practice was to change tanks using fuel gauge indications as a prompt, equating to roughly one-hour intervals. However, ATSB calculations showed some intervals were less than one hour. Effective fuel management requires regular in-flight fuel quantity checks, cross-checking available data, and recording fuel consumed and remaining per tank.
Emergency Procedures
An intermittent or partial engine power loss is an ambiguous condition. The pilot did not switch tanks, which was the necessary corrective action. Pilots should prepare for a complete engine power loss and follow applicable procedures to optimize recovery. Familiarity with ditching procedures is recommended.
Probable Cause
The ATSB determined that the engine power loss was probably due to a lack of usable fuel in the selected (right) tank, and the pilot did not select the other (left) tank, which contained usable fuel.