What happened
On July 10, 2004, a Cessna 402-B, registration EC-FCC, was taxiing toward runway 12 at Valencia Airport for a scheduled cargo flight to Palma de Mallorca. The aircraft, operated by Victor Echo, was carrying 300 kg of newspapers at the time of the incident. As the crew increased engine power to begin the takeoff roll, the left main landing gear leg suddenly collapsed. This failure caused the left wing and the left horizontal stabilizer to strike the runway pavement, while the tip of the left propeller also impacted the ground.
Both crew members on board escaped the incident without injuries, though the aircraft sustained important damage, including a deformed left wing, damaged landing gear components, and deformed propeller blades.
The investigation
Investigators examined the wreckage and focused on the mechanical failure of the landing gear assembly. The inspection revealed that the bellcranck pivot bolt had sheared, leading to the deformation of the forward fitting and the adjusting screw. The mechanical geometry of the overcenter locking mechanism was subsequently disturbed, causing the gear leg to retract into the gear well.
To identify the root cause, the broken bellcrank pivot bolt (P/N NAS 464P4-26) was sent to a laboratory for fractographic and chemical analysis. While the aircraft's maintenance records showed that the bolt had been replaced relatively recently—on August 14, 2003—and was well within its service life, the laboratory results provided a critical discovery regarding the component's integrity.
Findings
- The primary cause of the landing gear collapse was the shearing of the bellcrank pivot bolt.
- Laboratory analysis determined that the bolt's strength was significantly substandard; it measured 142 KSI, which is 11.25% lower than the minimum strength of 160 KSI required by the NAS464 specification.
- The failure was a static failure caused by shear loads, made possible because the bolt did not meet the necessary metallurgical strength standards.
- Maintenance records confirmed that the operator had followed all manufacturer instructions, and the bolt was still 616 landings away from its next required inspection.
- Inspection of the right main landing gear showed no abnormalities, ruling out a widespread misrigging error during maintenance.
Safety action
- It is recommended that Cessna Aircraft Company review the quality control systems of its vendors, specifically Honeywell TPG/Tristar, to ensure that all spare parts provided for assembly meet the required type design specifications.