What happened
On March 22, 2021, a Mitsubishi MU-2B-25, registration PT-JGA, was conducting a private passenger flight from Porto Velho to Ji-Paraná, Brazil. During the approach to Ji-Paraná Aerodrome (SBJI), the pilot discovered that the landing gear could not be deployed using the regular electrical system.
In an attempt to rectify the situation, the pilot initiated the emergency landing gear lowering procedure. According to the aircraft manual, this procedure requires approximately 130 movements of the emergency lever to release the doors and allow the gear to drop via gravity. However, the lever locked after only three actuations, preventing the gear from extending. The pilot subsequently performed a gear-up landing on the asphalt runway. The aircraft traveled 300 meters along the runway before coming to a stop, with the fuselage making contact with the side strip. The pilot and two passengers were unharmed, though the aircraft sustained minor damage to the fuselage and propeller blades.
The investigation
CENIPA investigators examined the aircraft's maintenance records and the mechanical components of the landing gear system. The investigation revealed that the airframe, engine, and propeller logbooks were not updated, and there were no specific maintenance records regarding the replacement or inspection of the landing gear safety pin.
To understand why the emergency system failed, investigators performed a mechanical strength test on the safety pin. While the manufacturer specifies a pin made of AA6061 alloy, chemical analysis revealed the installed pin was made of AA7075. This specific alloy possessed a much higher shear strength than required. During testing, the pin was subjected to a load of 1,553.3 kgf—well beyond the expected failure threshold of approximately 1,000 kgf—without shearing. Because the pin did not break, the mechanism could not release the gear doors.
Findings
- The use of a safety pin made of a different, stronger alloy than specified by the manufacturer prevented the emergency deployment of the landing gear.
- Maintenance records for the aircraft were incomplete, specifically regarding the landing gear and the history of the safety pin.
- The aircraft's logbooks were outdated, with some entries not updated since 2019.
- The pilot was qualified and experienced, and the flight was conducted within weight and balance limits under favorable weather conditions.