What happened
On 16 December 2009, a Piper PA 30, registration M-ALAN, was conducting a private flight from Guernsey to Ronaldsway. While cruising at 8,000 ft over the Irish Sea, the pilot identified a runaway propeller condition on the right engine. After attempting to stabilise the RPM through throttle and lever adjustments, the pilot shut down the right engine and began a diversion to Blackpool Airport.
Six minutes into this diversion, the left engine also lost power. The manifold pressure remained at 17 inches, which was insufficient to maintain level flight. Calculating that the aircraft could only glide approximately 12 nm and noting that Blackpool was 18 nm away, the pilot decided to ditch the aircraft near a gas rig support vessel. During the ditching, the aircraft struck the water in a "belly flop" manner. The pilot, who was uninjured, was rescued by a boat from a nearby vessel.
The investigation
The AAIB examined the wreckage, which had been submerged for five months and was heavily contaminated by seawater. The investigation focused on the mechanical condition of both engines and the propeller control systems.
For the right engine, investigators checked the propeller control governor and the propeller itself. While no mechanical anomalies were found, the air charge pressure was significantly lower than expected. For the left engine, the investigation concentrated on the fuel and ignition components. The examination of the fuel system and magnetos revealed no mechanical defects or evidence of fuel contamination.
Findings
- The right engine experienced an uncontrollable overspeed, which may have been caused by low air charge pressure or a stuck governor pilot valve.
- The left engine failed to produce sufficient power for level flight, though no mechanical cause could be identified.
- It is possible that induction icing on the impact tubes reduced fuel flow to the left engine.
- The pilot's decision to ditch near a support vessel likely facilitated a rapid rescue.