What happened
On October 6, 2009, an Aero Boero AB-115, registration PP-GNU, departed from the Goiânia Aerodrome, Brazil, for a flight instruction session. The aircraft was occupied by two crew members: an experienced instructor and a student pilot undergoing familiarization.
During the climb, as the aircraft reached approximately 4,500 feet, the crew experienced engine vibrations. This was followed by a continuous drop in RPM and a loss of engine power. The instructor took control of the aircraft as the engine failed completely. To avoid further complications, the instructor performed a forced landing in an open field near the city. During the descent, the aircraft struck a six-meter-tall tree before impacting the ground and sliding approximately 10 meters. Both occupants survived the accident without injuries.
The investigation
CENIPA investigators examined the aircraft and the circumstances surrounding the flight. While the fuel was found to be free of water contamination and the fuel lines were unobstructed, investigators identified significant issues with the electrical system.
The aircraft had been parked in an uncovered area the previous night during heavy rainfall. Investigators found that the rubber grommet in the firewall, which protects the magneto kill switch wiring as it passes through the engine compartment, was improperly installed. This allowed the wiring to come into contact with the aircraft structure.
Upon inspection, the magneto wiring showed signs of severe wear, including exposed cores, burn marks, and evidence of friction against the airframe. The investigation determined that moisture from the previous night's rain had accumulated in the wiring passage. This moisture triggered a short circuit, which caused the magneto wires to contact the aircraft's ground (mass). This electrical fault likely interrupted the ignition to the eight spark plugs, resulting in the engine failure.
Findings
- Electrical short-circuit caused by moisture accumulation in the firewall wiring passage.
- Improper maintenance of the aircraft wiring, specifically the failure to ensure adequate protection of the magneto cables.
- Inadequate management supervision regarding maintenance processes.
- Exposure of the aircraft to heavy rain due to overnight parking in an uncovered area.