What happened
On September 14, 2002, an ATR 42-300, registration PT-MTS, operated by Total Linhas Aéreas S/A, was performing a cargo flight for the Brazilian Postal Service (Correios) from Guarulhos (SBGR) to Londrina (SBLO). The aircraft climbed to Flight Level 180 and maintained normal communications with air traffic control until approximately 05:40P.
During the flight, the aircraft experienced a sudden and severe pitch trim runaway. The crew attempted to manage the emergency, but the aircraft eventually collided with the ground in the municipality of Estância de Paranapan and São Paulo. The impact occurred at a high velocity of approximately 366 knots. The aircraft was completely destroyed, and both pilots on board were killed.
The investigation
CENIPA's investigation focused on the mechanical failure of the pitch trim system and the crew's response. Investigators examined the aircraft's maintenance logs, which revealed that a trim control panel had recently been swapped between aircraft. The investigation also scrutinized the operational testing procedures outlined in the technical instructions (JIC 27-32-00), finding that the wording was ambiguous, which could allow for incomplete verification of the relays.
Technical analysis identified that failures in specific relays (15CG and 16CG) could lead to an uncommanded nose-up or nose-down trim movement if certain conditions were met. Furthermore, the investigation looked into the lack of specific emergency procedures in the manufacturer's manuals regarding trim runaway events and the lack of independent redundancy in the trim system's actuators.
Findings
- Design Flaw: The pitch trim system lacked sufficient independence between the primary and standby systems and had a low tolerance for error.
- Maintenance/Testing Ambiguity: The operational test procedure (JIC 27-32-00) was not sufficiently clear, potentially allowing an aircraft with a failed relay to be released for flight.
- Human Factors: The crew's ability to respond was hindered by a lack of specific training for this particular emergency and a lack of clear communication during the high-stress event.
- Operational Deficiencies: The operator had not provided regular Crew Resource Management (CRM) training, and the pilot had not participated in simulator training for over a year.