What happened
On April 11, 2007, a private Beechcraft A23-24 Muskster, registration EC-BMA, departed Alicante airport on a VFR flight. While cruising at 1,000 feet, the pilot experienced a sudden drop in engine RPM, falling from 2,200 to between 1,800 and 2,000. Despite attempts to recover power by advancing the power and propeller levers and leaning the mixture, the engine failed to regain performance, leading to a descent.
Recognizing the imminent need to land, the pilot notified air traffic control of his intention to land at Tabarca. Before impact, the pilot shut down the engine and moved to the right seat to facilitate an exit, as the left-side door was unavailable. The aircraft performed a water landing approximately 0.5 miles from the island of Tabrica. The aircraft sank, but the pilot successfully exited the craft and utilized a life vest. He was rescued by a nearby fishing vessel and later treated for hypothermia.
The investigation
The investigation focused on the engine's performance and the mechanical state of the aircraft. While initial inspections of the fuel lines and fuel supply showed no obstructions, the engine was subsequently dismantled by the CIAIAC.
Investigators discovered that an alternative air tube, designed to prevent intake icing, was incorrectly positioned. This tube was found to be in contact with the engine intake, which forced the fuel injector's spring-loaded door to remain open. Technical consultation with the airframe manufacturer revealed that the installation of this tube did not meet specifications; the tube was not positioned at the required distance from the cylinder head, and an incorrect type of clamp had been used. While maintenance records indicated the tube was correctly situated during a July 2006 inspection, the investigation concluded the tube had likely shifted into its improper position due to the incorrect installation or a mechanical jolt.
Findings
- The loss of engine power was caused by the admission of hot air into the engine intake.
- The alternative air tube was improperly installed, using an incorrect clamp and failing to meet the manufacturer's specified clearance distances.
- The position of the tube caused the fuel injector's spring-loaded door to stay open, allowing high-temperature air to enter the intake, which reduces engine output.
- The pilot's decision to shut down the engine and prepare for ditching was a response to the unrecoverable drop in RPM.