What happened
On October 2, 2016, a Tecnam P2006T was conducting a flight examination for a Multi-Engine Piston (MEP) rating in the vicinity of Wyszków, Poland. As part of the examination syllabus, the pilot performed a maneuver involving the intentional shutdown and subsequent in-flight restart of one engine. While the initial shutdown was performed correctly, multiple attempts to restart the engine were unsuccessful.
As the restart attempts continued, the aircraft's battery became depleted. Due to the loss of electrical power, the crew could not verify the landing gear position via cockpit instruments. During the return flight, another aircraft established communication with the Belloc (EPBC) aerodrome to report the situation, noting that the aircraft was returning without radio communication and with unverified gear status. Consequently, the landing gear was deployed via the emergency extension system. The pilot performed a low approach to runway 28 at EPBC to visually confirm the gear deployment and subsequently landed on the grass runway 10 without further incident.
The investigation
The investigation examined the aircraft's electrical configuration and the sequence of the engine restart attempts. It was established that the specific aircraft involved, serial number 66 (SP-MAC), utilizes a single battery for both engine starting and avionics power. The established procedure for an in-flight restart requires the shutdown of both electrical buses. During this period, the battery must provide power for the starter and maintain essential avionics, such as the Primary Flight Display (PFD). However, while both buses are disconnected, the alternator from the operating engine is unable to charge the battery or power any aircraft systems.
Post-flight inspections by a maintenance organization found no mechanical defects. Both engines were tested on the ground and functioned normally, and the alternator was found to be operational. The aircraft was cleared to return to service after a flight to a maintenance base for further verification.
Findings
- The primary cause of the engine failure to restart remains undetermined, though potential contributing factors included uncoordinated flight, a closed fuel valve, incorrect fuel pump settings, or failure to engage the magnetos.
- The depletion of the battery was caused by the electrical configuration of the aircraft, where the disconnection of both electrical buses prevented the alternator from recharging the battery during the restart attempts.
- Variations in equipment between different Tecnam P2006T models, specifically the presence or absence of an additional starter battery, may have influenced the pilot's expectations regarding power availability.