Investigation Summary
The accident occurred during a routine mail flight from São Paulo to Londrina. While cruising at FL180, the autopilot suddenly disengaged and the pitch trim system began moving the elevator trim tabs to a full nose-down attitude. Shortly before the failure, the captain had removed himself from his seat to change clothes, though investigators determined he remained within the cockpit area. Although the captain quickly returned to his seat and identified the issue as a trim runaway, communication difficulties and the co-pilot's initial confusion delayed the critical action of pulling the pitch trim circuit breaker. By the time the breaker was deactivated, the aircraft had already accelerated past its maximum operating speed (Vmo). The crew attempted to arrest the descent by pulling back on the control columns with significant force, but the aerodynamic loads at high speed, combined with the full nose-down trim, made recovery impossible. The aircraft impacted the ground in a 45 degree nose-down attitude with a 30 degree left bank.
Final Conclusions
CENIPA released its final report (A-006/CENIPA/2007) on March 30, 2007. The primary cause was a failure in the pitch trim system, likely due to defective relays, switches, or wiring, which triggered a continuous nose-down command. Contributing factors included the lack of a manufacturer-provided emergency procedure for runaway trim, inadequate crew training for such scenarios, and poor cockpit resource management (CRM) during the emergency. The investigation also noted that the normal and standby trim systems were not sufficiently independent, allowing a single failure to compromise the aircraft's controllability.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Pitch Trim Control System
A system that adjusts the elevator trim tabs to reduce the control column forces required to maintain a specific pitch attitude. In this accident, a relay or wiring failure caused a 'runaway' where the system moved the tabs to the full nose-down limit without pilot input.
Pitch Trim Circuit Breaker
A protective switch located on a panel behind the co-pilot. Pulling this breaker is the primary method to cut power to a runaway trim motor, but the pilot cannot reach it from the left seat.
Interesting Facts
- 01The aircraft was manufactured in 1986 and was 16 years old at the time of the accident.
- 02The pitch trim reached its full down stop of five degrees during the runaway.
- 03The aircraft exceeded its maximum operating limit speed (Vmo), reaching 366 knots before impact.
- 04No emergency checklist for a runaway trim scenario existed in the manufacturer's manuals at the time.
- 05The captain had not received simulator training for over one year prior to the accident.
Safety Actions & Advisories
Emergency Procedures Update
The investigation highlighted the lack of a runaway trim checklist, leading to recommendations for manufacturers to include specific procedures for uncommanded compensator activation in flight manuals.
System Independence Review
Investigators recommended reviewing the design of the ATR 42 pitch trim system to ensure that normal and standby systems are truly independent and tolerant of single-point failures.
Maintenance Time Limits
The report noted a lack of defined replacement intervals for elevator trim system components in the 'Time Limits' section of maintenance manuals, leading to recommendations for establishing component life limits.
Location
ACCIDENT SITE · Coordinates taken from the official investigation report.