History of Flight
On January 10, 2009, at approximately 1100 Pacific standard time, a Cessna 172RG, registration N6272R, landed at Carson Airport in Carson City, Nevada, with the right main landing gear only partially extended. The airplane was operated by National Pilot Academy under 14 Code of Federal Regulations Part 91. The flight, which departed Carson Airport around 0930, was a local personal flight. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot reported that after an uneventful preflight, takeoff, and practice area flight, he began returning to Carson City. About five minutes into the return, he heard a loud clunk from beneath the airplane, which he initially attributed to the hydraulic system. When the sound repeated a few minutes later, he became concerned. While on the crosswind leg for landing, he attempted to lower the landing gear but observed an unsafe indication on the gear indicator lights. A visual check confirmed the right main gear had not fully extended. He recycled the gear system, operated the manual pump, and performed load-inducing maneuvers, but the gear remained partially extended. After consulting with maintenance personnel, he landed with the nose and left landing gear retracted. During the landing, the airplane sustained substantial damage to the belly structure.
Tests and Research
Examination of the right main landing gear actuator revealed fractures around its mounting holes, suggesting failure. The operator reported a similar failure on another Cessna 172RG in their fleet (N5242V) and retained the failed part. Both actuators—from N6272R and N5242V—were sent to the Safety Board Materials Laboratory for analysis.
The accident actuator body (part number 9882015-2, serial number 4580, assembly date fourth quarter 1979) showed cracks at three locations near the sector gear opening. One crack at the forward mounting hole propagated through the entire body, leaving a gap. A second crack between the inner body and rear mounting hole had not fully opened, and a third crack near the piston roller bearing was similarly incomplete. Microscopic examination of the forward hole fracture revealed ductile dimples typical of overload. The piston exhibited mechanical damage to its forward edge and scoring on gear teeth consistent with gear contact.
The exemplar actuator from N5242V showed similar cracks at the forward and aft mounting holes but not at the roller bearing. Its piston and rack had similar mechanical damage, and the sector gear had arc-shaped indentations on the last fully engaged tooth when the landing gear was retracted.
An installation examination on an exemplar airframe found no provisions for rigging adjustment; extension and retraction were controlled by end-stops and micro-switches. With the actuator cap removed, cycling the gear showed no impingement of sector gear teeth on the piston surface adjacent to the rack.
Maintenance Records
An FAA inspector reviewed the airplane's maintenance logbooks and found no entry for compliance with Cessna Service Bulletin SEB01-2, which addresses repeated inspections for fatigue-induced cracks in the actuator body near the piston roller bearing. The operator's 100-hour inspection control log also lacked an entry for this bulletin. The last 100-hour inspection occurred on January 8, 2009, at 5,031 total airframe hours. NTSB laboratory examination did not observe the polishing required by the service bulletin.