What happened
On October 21, 1999, an Aero Commander 500S, registration PP-SEA, operated by CETTA Táxi Aéreo, was performing a multi-leg cargo flight transporting mail and medicines across northeastern Brazil. The flight originated in Recife, with scheduled stops in several cities including Patos, Souza, Moss and Caicó, before returning to Recife.
After approximately 3 hours and 50 minutes of flight time, while descending toward Recife on the final leg of the circuit, both engines failed. The pilot declared an emergency, reporting that the aircraft was 10 nautical miles from Recife and required a forced landing. During the attempt to land in an open area, the pilot deployed the landing gear and flaps. While attempting to reduce speed, the pilot realized the aircraft would overshoot the chosen landing site and commanded the gear to be retracted. During this maneuver, the left main landing gear struck a tree and subsequently hit power lines. The aircraft then impacted an irregular surface covered in dense vegetation.
The two crew members sustained minor injuries and were rescued by local residents and a Brazilian Air Force helicopter approximately 30 minutes after the accident. The aircraft sustained severe damage.
The investigation
CENIPA investigators determined that the engines failed due to a total lack of fuel. While the crew believed a fuel leak had occurred, inspections of the fuel system, lines, and engine cowlings showed no evidence of leakage or structural integrity issues.
The investigation examined the refueling process and found that the pilot used an empirical, inaccurate fuel consumption rate of 115 liters/hour, whereas the actual consumption was approximately 120 liters/hour. Furthermore, the pilot's flight planning failed to account for taxi time or the impact of headwinds.
Technical analysis of the aircraft's fuel system revealed that the single refueling point on the right wing, combined with the wing dihedral, could lead to the formation of air bubbles. This could create a false impression that the tanks were full when they were not. Additionally, the aircraft's fuel gauge (liquidometer) was found to be insufficient, as it could only indicate up to 135 gallons, while the total capacity was 156 gallons.
Findings
- Fuel Exhaustion: The primary cause of the engine failure was the total depletion of fuel.
- Inaccurate Planning: The pilot utilized an incorrect hourly fuel consumption estimate and failed to account for taxiing and wind conditions.
- Human Factors: An excess of confidence due to flight familiarity, combined with a lack of Crew Resource Management (CRM), led to a reduction in situational awareness and a failure to cross-check fuel calculations.
- Design Deficiencies: The fuel system design allowed for air bubbles to mask low fuel levels, and the fuel gauge was incapable of measuring the full capacity of the tanks.
- Operational Deficiencies: The operator lacked standardized procedures for fuel monitoring and flight planning, relying instead on the empirical methods of the pilot in command.