Incident
On 6 April 1999, a Cessna T500 registered F-GJDG, operated by Air Normandie, was conducting a check flight after maintenance at Le Havre aerodrome. The aircraft had two crew members and one passenger on board. After takeoff, the pilot actuated the electric trim control to nose-up. The aircraft progressively adopted a nose-down attitude, which the pilot attempted to counter by continuing to operate the trim control. The trim indicator reached the full nose-up stop, and the pilot had to exert significant nose-up force on the control column to maintain level flight. Speed increased and the aircraft continued descending to about 300 feet. The pilot reduced engine power to reduce speed, managed a low-altitude circuit with the elevator control near the aft stop, and landed the aircraft. No damage or injuries occurred.
Investigation
Post-flight inspection revealed that the cables actuating the elevator trim actuator were reversed. The colour coding on the new trim actuator housing was inverted: the upper part was painted orange instead of white, and the lower part white instead of orange. The mechanic connected the cables according to the colour code, resulting in reversed trim operation. The trim indicator in the cockpit showed full nose-up, consistent with the reversed control.
The trim actuator (part number 5565450-93 for French-registered aircraft) had been replaced during a major inspection by Air Normandie's JAR 145 approved workshop. The part was ordered from Cessna Europe, imported from Wichita. The aircraft, previously US-registered (N84AT), had modifications for French certification, including colour markings on control cables and terminals. The Cessna Parts Catalog specifies white and orange markings for French aircraft to prevent assembly errors.
Findings
The maintenance manual procedure for adjustment and test (27-30-00, pages 501-508) does not include a correlation between trim tab position and control direction during travel checks, though section 12 establishes it. Another procedure (Inspection/Check) has different deflection values but was not used. The mechanic did not detect the reversal; the colour code likely influenced him not to question the assembly direction.
The manufacturing error consisted of inverted colour markers on the trim actuator housing, contrary to the specified white on top and orange on bottom. This defect was not detected before installation.