What happened
On September 14, 2002, a Canadair CL-600 operating a charter flight from Cagliari, Italy, arrived at Munich Airport for an ILS approach to runway 26L. During the landing approach, the crew received a 'GEAR DISAGREE' warning, indicating that the nose landing gear (NLG) was not in the same position as the main landing gear. The crew subsequently aborted the landing and retracted the gear to attempt a reset. Despite several attempts using both normal and emergency extension procedures, the nose gear failed to extend and lock. During a flyby of the control tower, it was observed that only the nose gear doors were open, with no visible sign of the gear or tires.
Following the failed attempts, the crew prepared for a landing with the nose gear retracted. The aircraft touched down on the main gear at 120 kt, but at 80 kt, the nose of the fuselage made contact with the runway. The aircraft came to a halt on the runway centerline. Although no injuries were reported among the 49 passengers and 4 crew members, the aircraft sustained heavy damage, including destruction of the nose gear doors and abrasions to the fuselage skin and frames. Light smoke and the smell of burning were noted in the cockpit immediately after the aircraft stopped, prompting an evacuation.
The investigation
The BFU examined the aircraft's flight data recorder (FDR) and cockpit voice recorder (CVR), which confirmed the gear malfunction and the crew's adherence to emergency checklists. Maintenance records revealed that an A-check had been performed between September 4 and September 11, 2002, during which all landing gear components, including the NLG extension/retraction actuator and the uplock assembly, were replaced.
During the on-site investigation, the nose gear was found to have been mechanically held in the retracted position. Physical examination of the hydraulic system's return filter revealed metal shavings, which were identified as high-alloy Cr-Ni-Mn steel from a machining process. Further technical analysis of the uplock assembly revealed that the distance between the latch and the uplock pin in the locked position was significantly smaller than the required specification (0.09448 inches instead of the required 0.125 to 0.195 inches). Additionally, the uplock pin was found to be non-rotatable, creating excessive friction that prevented the gear from extending.
Findings
- The primary cause of the accident was that the nose landing gear was mechanically held in the retracted position due to an improper installation setting.
- The distance between the latch and the uplock pin in the locked position was too small, causing the pin to contact the latch.
- The uplock pin was not rotatable, which created high frictional forces that prevented the gear from releasing.
- The Aircraft Maintenance Manual (AMM) lacked specific instructions for verifying the required clearance between the latch and the pin during the installation of the nose landing gear and the uplock assembly.
- Maintenance instructions for the overhaul of the nose gear did not sufficiently emphasize the requirement for the uplock pin to remain rotatable.