What happened
On February 18, 2014, a privately operated Cessna 340, registration N876DT, departed from Vannes for a flight to Toussus-le-Noble. During the approach phase, the pilot noticed that the right main landing gear indicator remained red and a "gear unlocked" message appeared on the instrument panel. Despite attempting to cycle the landing gear and utilizing the manual extension crank, the pilot could not achieve a locked indication.
While the air traffic controller indicated that the gear appeared to be extended, the pilot proceeded with a precautionary landing on runway 25L, attempting to minimize stress on the gear. During the landing roll, the right main landing gear retracted, causing the aircraft to tilt to the right and veer off the runway into the grass. The incident resulted in no fatalities, but the aircraft sustained damage to the right wing and right propeller.
The investigation
The investigation focused on the mechanical failure of the landing gear assembly. The aircraft's landing gear system is driven by an electric motor, though a manual crank is available to bypass motor failure. However, both the electric motor and the manual crank operate the same underlying mechanism.
Physical examination of the landing gear revealed that the control rod for the right main gear actuation mechanism had failed at the ball joint connected to the bellcrank. The nature of the break allowed the rod to remain connected to the bellcrank, but it was unable to exert the necessary tensile force to lock the gear in the extended position. Fractographic analysis determined that the rod failed due to a tensile overload. No material defects, pre-existing damage, or geometric anomalies were identified in the component. Maintenance records indicated that no work had been performed on this specific part of the landing gear since the year 2000.
Findings
- The right main landing gear failed to lock in the down position because the control rod was broken.
- The failure of the control rod prevented the gear from being secured, even when using the manual extension method, because both the electric and manual systems rely on the same damaged mechanism.
- The breakage of the control rod was caused by a tensile overload, though the specific origin of this overload could not be determined.