What happened
On January 25, 2013, a Mitsubishi MU-2B-60, registration PR-JFN, departed from Aeródromo Santa Genoveva (SBGO) in Goiânia, Brazil, for a local flight. The purpose of the flight was to perform a functional check of the aircraft's pressurization system following the replacement of the cockpit windshield and side windows.
During the flight, the pilot reached flight level 240 but encountered icing conditions, prompting a return to the airfield. During the landing approach, the pilot attempted to extend the landing gear but noticed that the "gear in transit" light remained illuminated. After attempting to resolve the issue through coordination with air traffic control and an unsuccessful attempt to cycle the gear—which caused a circuit breaker to trip—the pilot declared an emergency. The pilot ultimately decided to land on runway 32 with the landing gear retracted. The aircraft sustained substantial damage during the landing, and the airfield was temporarily closed, though the pilot escaped uninjured.
The investigation
CENIPA investigators examined the landing gear mechanism and discovered that the shear pin installed in the main landing gear door release shaft was not the original part. While the required part (PN: 035A-38864) is made of an aluminum 7075 alloy, the installed pin was a custom-machined component made of a copper alloy (brass USN C37700). This substitute material was significantly harder and lacked the necessary properties to shear under pressure, which prevented the doors from opening via gravity during an emergency deployment attempt.
Furthermore, the investigation identified mechanical discrepancies in the emergency operation system. The locking hook for the left main landing gear door was improperly adjusted, resulting in a smaller gap between the hook and the door roller compared to the right side. This misalignment kept the left door locked, blocking the landing gear leg from extending. Additionally, a conduit terminal for the cable connecting to the left door mechanism was found displaced from its fixation point.
Findings
- Improper maintenance of the aircraft, specifically the installation of a non-standard, incorrectly specified shear pin.
- Inadequate supervision regarding maintenance practices.
- The use of a brass alloy pin instead of the specified aluminum alloy prevented the mechanical release of the landing gear doors.
- Mechanical misalignment of the left main landing gear door locking hook prevented the emergency extension sequence.