What happened
On May 18, 2007, a Diamond DA 40D departed Hof-Plauen airport for a VFR flight to Calvi, Corsica. During taxi and early flight, the passenger noted several "Attention" indications on the instrument panel, though the pilot reported seeing no warning lights prior to takeoff. Approximately 30 minutes into the flight, the integrated avionics displays failed. The crew abandoned the original destination and attempted to navigate using a handheld GPS and a radio powered by batteries.
At 12:10 PM, while approximately 32 NM south of Bayreuth, the engine experienced a brief failure. Although the pilot managed to restart the engine using the emergency battery, subsequent engine failures occurred repeatedly starting at 12:14 PM. During the approach to Bayreuth airport, the pilot was unable to confirm altitude or airspeed due to the lack of available GPS data. The aircraft touched down on a grass strip near runway 24, but failed to stop on the airfield. The aircraft crossed an adjacent road and collided with an embankment, resulting in two serious injuries and heavy damage to the aircraft.
The investigation
The BFU examined the electrical system, the engine control units (ECU), and the aircraft's documentation. Investigators found that the alternator's cable lug had broken, and the connection point showed evidence of melting. The investigation also reviewed the Garmin G1000 avionics behavior, noting that displays fail when voltage drops below 8.3V. Furthermore, the investigators analyzed the Pilot Operating Handbook (POH), finding that instructions regarding the backup instruments and the organization of abnormal procedures were potentially confusing or incomplete.
Findings
- The primary cause of the electrical failure was a broken cable lug at the alternator, which interrupted the aircraft's power supply.
- The pilot failed to respond to the "LOW VOLTS" caution during the pre-flight and early flight phases.
- Insufficient system knowledge led to a delayed decision to perform a precautionary landing.
- The loss of electrical supply to the ECU eventually caused the engine to fail.
- The pilot's landing technique was inadequate, causing the aircraft to overshoot the airfield boundaries.
- The backup altimeter was incorrectly set, as the POH lacked specific instructions for preparing backup instruments.