What happened
On April 6, 1999, a Cessna T500, registration F-GJDG, operated by Air Normandie, was performing a maintenance test flight at Le Havre aerodrome. Following takeoff, the pilot attempted to use the electric trim to pitch the aircraft up. Instead, the aircraft began to enter a progressive nose-down attitude.
As the pilot continued to apply nose-up trim to compensate, the aircraft's speed increased and the descent deepened. At an altitude of approximately 30/0 feet, the pilot responded by reducing engine power to decrease airspeed. This reduction in aerodynamic forces allowed the pilot to maintain control and complete a low-altitude circuit to land the aircraft safely. Upon ground inspection, it was discovered that the cables operating the elevator trim actuator were installed in reverse.
The investigation
The investigation focused on the recent maintenance performed on the aircraft, specifically the replacement of the trim actuator cylinder. The component had been replaced during a major inspection by an approved maintenance facility. The new part had been ordered from Cessna Europe and imported from the manufacturer's facility in Wichita.
Investigators examined the color-coding system used to prevent installation errors on French-registered aircraft. For these aircraft, specific color markers (white or orange) are applied to cables and components to ensure correct assembly. The investigation revealed that the new actuator arrived with the color-coded markers on the housing reversed: the upper portion was orange and the lower portion was white, which was the opposite of the required configuration.
Findings
- The primary cause of the pitch control issue was the reversed installation of the trim control cables.
- A manufacturing error at the factory resulted in the inversion of the color-coded identification markers on the new trim actuator.
- The maintenance technician failed to detect the error during installation because the color-coded markers strongly suggested the incorrect connection was correct.
- The pilot was unable to identify the source of the malfunction during flight because the cockpit trim indicator and the trim wheel both showed a full nose-up position, masking the actual aerodynamic effect of the reversed cables.