What happened
On June 5, 2011, a Piper PA-34-200T Seneca II, registration HB-LSD, departed from Son Bonet, Spain, on an IFR flight toward Basel-Mulhouse with three passengers. During the flight at FL110, the pilot noticed the left engine alternator charge indicator dropping toward zero, while the right engine showed approximately 35 amps. After attempting to reset the alternators, the pilot began shedding electrical loads, retaining only essential communication, navigation, and GPS functions.
Approximately 20 minutes later, the flight director began providing erroneous information, prompting the pilot to disengage the autopilot. As weather conditions deteriorated near the Martigues VOR, the pilot activated the weather radar, but shortly after, the right alternator charge dropped to 5A with intermittent warning lights. Following a second load shedding, the aircraft suffered a total electrical failure.
Unable to contact air traffic control before the failure, the pilot descended to 1,000 feet to clear the cloud layer and initially intended to divert to Avignon. However, encountering a thunderstorm, the pilot diverted to Nîmes Garons. During the landing configuration, the pilot was unable to successfully operate the mechanical emergency gear extension. Due to the approaching storm, the pilot proceeded to land with the landing gear retracted, resulting in heavy damage to the aircraft.
The investigation
The investigation focused on the cause of the electrical failure and the failure of the emergency gear extension. Regarding the landing gear, inspectors found no mechanical malfunction in the emergency extension system; the procedure requires moving a metal cover to access the manual control.
Regarding the electrical system, the left engine alternator had been replaced shortly before the flight. The pilot had previously requested a maintenance check because the alternators were showing unbalanced loads, and the technician had noted that a satisfactory adjustment could not be achieved and was scheduled to be completed after the flight. Post-accident analysis revealed that a component within the drive mechanism of both alternators had failed.