What happened
On January 16, 2016, a Mooney M20B, registration PP-SID, was conducting a training flight consisting of touch-and-go maneuvers at the Apucarana (SSAP) and Governador José Richa (SBLO) aerodromes. The flight originated from the Silvio Name Junior Airport (SBMG) in Maringá, Brazil.
Upon returning to SBMG, the aircraft landed as planned. However, during the landing roll, the nose and main landing gear inadvertently retracted. This caused the aircraft to drag along the runway, veering to the left—likely because the left main gear retracted before the right—until it came to a complete stop. The aircraft sustained substantial damage, though both the pilot and the passenger were unharmed.
The investigation
The CENIPA investigation focused on the mechanics of the landing gear control lever and the runway conditions. Investigators examined the M20B's landing gear system, noting that to extend the gear, the control lever must be pulled vertically into a specific receptacle where a spring-loaded transverse pin locks it in place. To retract the gear, the pin must be compressed while the lever is moved downward.
Testing revealed a critical vulnerability in the cockpit's indication system: when the lever was placed in the receptacle, the green light would illuminate and the gear-unlocked warning alarm would disarm even if the lever had not been fully locked. This could create a false sense of security regarding the gear's status.
Additionally, the investigation looked into the runway surface at SBMG. Records indicated that the pavement on runway 10 had experienced degradation, with irregularities noted as early as December 2015. The investigators considered whether vibrations caused by this degraded pavement could have caused the control lever to shift out of its receptacle or interfered with the microswitches intended to prevent inadvertent retraction on the ground.
Findings
- The landing gear control lever may have shifted out of its locking position during the landing roll.
- The aircraft's cockpit indication system could provide misleading information, showing the gear as locked even if the lever was not fully seated in the receptacle.
- Degraded runway pavement at the airport may have contributed to the incident by inducing vibrations that facilitated the movement of the control lever.