What happened
On March 9, 1983, at approximately 18:30, a Cessna A 188B agricultural aircraft, registration CS-AHS, was performing a flight from Salvaterra to Coruche. The aircraft, operated by FOMAL, had just completed aerial spraying applications and was returning to the Casas Novas landing strip. During the flight, the engine suffered an unexpected and total failure.
The pilot attempted an emergency landing in a field at Herdade de Mata Lobos – Biscainha. Although the pilot successfully reached the field, the ground was saturated with water. As the aircraft touched down, the left wheel sank into the soft soil, causing the aircraft to lose stability and capsize. There were no fatalities and the pilot escaped without injury.
The investigation
The GPIAAF investigation focused on the cause of the engine failure and the subsequent aircraft behavior. Investigators examined the aircraft's fuel system and performed tests on the fuel quantity indicator. The investigation confirmed that the engine stopped because the fuel tanks were empty.
Technical tests conducted at the Aeroavia workshop revealed that the fuel gauge was providing highly inaccurate readings. When fuel was added to the aircraft, the gauge failed to correspond to the actual volume; for example, while the gauge indicated a level of approximately 1/8 to 1/4 of the tank, the actual amount of fuel remaining was insufficient to maintain engine operation. The investigation also noted that the aircraft's engine and propeller were recoverable, though the airframe sustained damage to the cowling, windshield, and vertical stabilizer due to the rollover.
Findings
- The primary cause of the engine failure was fuel exhaustion.
- The fuel quantity indicator was malfunctioning, providing false readings that led the pilot to believe sufficient fuel remained for the flight.
- The soft, wet condition of the landing site contributed to the aircraft's wheels sinking and the subsequent capsize.
- The pilot was properly certified and qualified for the specific type of agricultural operation being performed.