What happened
On Wednesday, December 10, 1997, at 11:25 AM, a Cessna T 337 G (registration D-ICHO) was performing a private flight when the pilot encountered difficulties with the landing gear deployment. During the approach for landing, the pilot commanded the gear to extend. While the unlocking mechanism engaged, the green indicator light failed to illuminate, and the hydraulic pump continued to run, indicating the gear was not properly locked.
The pilot attempted emergency deployment procedures, but these were unsuccessful. Although the relative wind caused the nose gear to lock into position, the main landing gear legs remained unsecured and hanging. Due to the gear configuration, the pilot elected to perform a precautionary landing on the paved runway at Cannes-Mandelieu. Upon touchdown, the main landing gear collapsed, causing the aircraft to come to a halt after sustaining significant damage to the propeller, gear doors, the lower fuselage, and the dual vertical stabilizers.
There were two persons on board, and no fatalities were reported.
The investigation
The investigation focused on the mechanical failure of the landing gear system. Investigators examined the hydraulic components and the maintenance history of the aircraft. The inspection of the hydraulic actuator revealed that the body of one of the main gear command cylinders had a longitudinal split. This fracture resulted in a significant loss of hydraulic fluid, preventing the gear from extending and locking.
Regarding maintenance, the investigation found that the aircraft's maintenance manual did not explicitly require a detailed inspection of these specific actuators; the manual only mandated the periodic replacement of O-rings. While a visual inspection of the cylinders had been performed during the most recent O-ring replacement, the aircraft had completed approximately fifty landings since that service. The pilot's pre-flight inspection had not revealed any abnormalities.
Findings
- The primary cause of the landing gear failure was the rupture of a landing gear command actuator.
- The longitudinal split in the actuator body caused a hydraulic fluid leak, which prevented the gear from reaching the locked position.
- The existing maintenance program focused on O-ring replacement rather than structural inspections of the actuator bodies.
- The pilot's pre-flight inspection was unable to detect the internal structural failure of the component.