What happened
On July 3, 2006, at approximately 17:30 UTC, a Cessna 402 B, registration EC-ERH, departed from Cuatro Vientos Airport in Madrid for a local test flight. The crew, consisting of a pilot, co-pilot, and mechanic, intended to perform various maneuvers and configuration changes as part of a post-maintenance inspection following a 200-hour annual review.
After completing several maneuvers and requesting permission for touch-and-go operations, the crew performed a smooth landing. During the subsequent takeoff roll, the pilot noticed the aircraft drifting to the right and observed that the right wing was dropping. The pilot immediately cut the engines and alerted the crew to the imminent runway excursion. The aircraft veered to the right and came to a stop approximately 15 meters outside the right edge of the runway.
All 3 occupants escaped without injury. The aircraft sustained minor damage, including a collapsed right main gear, damage to the landing gear door, and deformation to the right flap, aileron, and horizontal stabilizer.
The investigation
The CIAIAC examined the wreckage of the right main landing gear assembly. Investigators found that the bellcrank was loose from its connection to the gear leg due to a broken pivot bolt. Additionally, one of the bellcrank's lugs had fractured due to tension or bending forces.
Laboratory analysis of the bellcrank pivot bolt revealed that the bolt had failed via a ductile shear process caused by overload. While the bolt's hardness exceeded the specified range, investigators noted that work hardening during the failure process could have altered the measured values.
Further investigation into the landing gear mechanism—which uses an electric motor and a series of rods to actuate the gear—focused on the overcenter locking mechanism. The investigation included a comparison with a similar Cessna A-310 to evaluate wear and adjustment procedures. The investigators determined that the mechanical components were subject to lateral loads that the system was not designed to withstand if the geometry was improperly configured.
Findings
- The right main landing gear leg collapsed during the takeoff roll.
- The bellcrank pivot bolt failed due to shear overload.
- A lug on the bellcrank fractured due to tensile or bending stress.
- The failure was triggered by a redistribution of forces caused by an improper adjustment or a shift in the overcenter locking mechanism.
- The investigation concluded that the mechanism was likely adjusted slightly outside of the proper overcenter position, or that accumulated tolerances in the linkage allowed the mechanism to move out of its secure locking state.