What happened
On May 19, 2012, a Cessna 3/10R, registration PT-GMA, departed from Guanambi, Bahia, en route to Aeródromo Fazenda do Morro. Due to unfavorable weather conditions, the pilot diverted the flight to the Amargosa airfield (SNAZ).
During the landing roll at Amargosa, the right main landing gear began to gradually retract. Upon noticing the malfunction, the pilot shut down the corresponding engine. The aircraft subsequently drifted to the right and came to a stop off the runway. All three occupants—the pilot and two passengers—were uninjured, but the aircraft sustained substantial damage.
The investigation
CENIPA investigators examined the landing gear system and found that several components had failed, including the pivot bolt, the truss assembly support (ear), and the downlock link adjusting screw.
The investigation established that the downlock link was not functioning correctly, preventing the upper and lower side links from reaching the overcenter position. This interrupted the locking cycle, causing irregular stress distribution across the landing gear leg, the downlock link, and the associated mounting hardware. This irregular stress led to the structural failure of the components and the subsequent unintended retraction of the gear.
Crucially, the investigation found that the downlock indicator switch functioned normally, providing a green light to the cockpit indicating the gear was down and locked, which masked the underlying mechanical issue.
Findings
- Inadequate adjustment of the main landing gear retraction system was the primary factor leading to the mechanical failure.
- The failure of the downlock link prevented the gear from reaching a secure overcenter position.
- The resulting irregular distribution of forces caused the fracture of the pivot bolt, the truss assembly support, and the adjusting screw.
- The pilot's cockpit indications (green light) were misleading because the indicator switch was still triggered despite the improper mechanical lock.