What happened
On August 6, 2004, a Moragón M-1 ultralight aircraft, registration CS-UMS, departed from Santarém aerodrome for a recreational flight to Alqueidão. Approximately ten minutes into the flight, while cruising at 1,000 feet, the engine suffered a sudden and complete stoppage. The pilot attempted to restart the engine using the manufacturer's recommended procedures, but was unsuccessful.
Following the engine failure, the pilot executed an emergency landing in a flat, unobstructed field on the left bank of the Tejo River, near Mouchão, close to Muge. The aircraft landed into the wind and rolled for approximately 50 meters. During the final part of the landing roll, the nose gear collapsed, causing the nose of the aircraft to strike the ground. This impact damaged the propeller, the engine cowling, and the landing gear. The pilot and passenger were uninjured.
The investigation
The GPIAAF investigation focused on the electrical system and the recent maintenance performed on the aircraft. Investigators found that the instrument panel, switches, and electrical wiring had been replaced a few weeks prior to the accident. However, this work had not been certified by the competent aeronautical authority, nor had it been recorded in the aircraft's documentation.
Upon examining the electrical system, investigators discovered that the electrical terminals were secured with simple nuts and washers, lacking any locking or self-retaining mechanisms. Due to engine vibrations, these nuts had loosened, creating intermittent connectivity. This loose connection caused electrical sparking between the terminals and the fixing bolts. These sparks created an electrical overload that caused the main circuit breaker to trip, effectively cutting power to the ignition system and causing the engine to stop.
Findings
- The primary cause of the engine failure was a loss of electrical power to the ignition system caused by the tripping of the main circuit breaker.
- The circuit breaker tripped due to electrical discharges (sparking) resulting from improperly secured electrical terminals.
- The use of non-aviation standard fasteners (simple nuts without locking mechanisms) allowed vibrations to loosen the terminals.
- The engine lacked an independent high-voltage ignition system (such as a magneto) that could maintain operation during a general electrical failure.
- The recent installation of the instrument panel and wiring was not performed according to applicable aeronautical standards and was not properly documented.