History of Flight
On May 1, 2013, about 1445 Pacific daylight time, a Cessna 421A, N216WA, experienced a left main landing gear collapse during landing rollout at Metropolitan Oakland International Airport (OAK), Oakland, California. The airline transport pilot and the pilot-rated owner were not injured. The personal flight was conducted under 14 Code of Federal Regulations Part 91 in visual meteorological conditions. No flight plan was filed for the local flight, which had departed Buchanan Field (CCR), Concord, California, about 1330.
Earlier in the day, the pilot had performed several touch-and-go landings at CCR. On a later flight with the airplane owner, they conducted a touch-and-go at another airport, a low approach at a third airport, and then planned to land at OAK. During the approach to runway 27R, both the pilot and owner independently verified landing gear extension by observing the position indicator lights. The touchdown was normal, but immediately after, the left wing dropped and the airplane veered left. It exited the left side of the runway and came to rest upright. The occupants exited and observed that the left main landing gear (LMLG) had collapsed.
Personnel Information
The pilot held an airline transport pilot certificate with multiple ratings and reported approximately 6,720 total flight hours, including about 200 hours in the accident airplane make and model. His most recent flight review and FAA third-class medical certificate were completed in October 2012.
Aircraft Information
The airplane was manufactured in 1969 and equipped with two Continental Motors GTSIO-520 series engines. It was acquired by its current owner in October 2007.
Meteorological Information
The 1453 automated weather observation at OAK reported wind from 310 degrees at 12 knots, visibility 10 miles, clear skies, temperature 26°C, dew point 9°C, and an altimeter setting of 30.02 inches of mercury.
Wreckage and Impact Information
The airplane struck a taxiway sign and came to rest off the left side of runway 27R. The left engine propeller blades contacted the pavement, resulting in damage. The left fuel tip tank and left wing, including the spar and aileron, sustained substantial damage. Portions of the left main landing gear linkage were also damaged. One lug on the upper landing gear leg was fracture-separated, and the pivot bolt installed through a bushed hole at the apex of the bellcrank and the landing gear trunnion was fractured. The forward clevis lug of the lower end of the main landing gear bellcrank was also fracture-separated.
Maintenance and Component Examination
The landing gear system uses a single motor to extend and retract all three gears via push-pull rods and links. The main landing gear extends outboard and locks in the extended position by an overcenter positioning of side braces. The bellcrank pivot bolt failure would prevent the side brace from locking, allowing collapse under load.
In June 2006, the airplane experienced a similar LMLG collapse on landing due to a pivot bolt failure. At that time, the total time (TT) was 3,463.5 hours. Lane Aviation replaced the bolt and bellcrank, and the airplane returned to service in June 2007. The current owner purchased the airplane after those repairs. Maintenance records show an annual inspection and complete landing gear rigging in November 2007 by TAS Aviation. Subsequent maintenance included corrections to LMLG door spacers (July 2009) and a right main landing gear grease fitting replacement (November 2010). The most recent annual inspection was in January 2013, during which the main landing gear shock struts were serviced.
The bolt that failed in the accident had accumulated only 226.5 hours since installation. None of the maintenance records explicitly referenced compliance with Cessna Supplemental Inspection Document (SID) or Continued Airworthiness Inspection (CAI) 32-10-03, which detail inspection and replacement of the bellcrank pivot bolt. The Cessna 421 Service Manual warns that any time a landing gear component is removed or replaced, the entire system must be re-rigged.
Examination of the bellcrank assembly (part number 5041001-1) at the NTSB Materials Laboratory revealed an overstress fracture on one clevis lug and the bolt. The bolt fracture occurred in the shank about 0.3 inches from the head, consistent with overstress shear. The bolt met specifications (NAS6204 26D) with hardness within allowable range.
Previous Similar Events
The Spanish investigative agency (CIAIAC) reported a similar event on April 6, 2006, involving a Cessna 421 (EC-IPO), where shear failure of the bellcrank pivot bolt was a principal factor. That report cited 11 previous similar events on Cessna 300- and 400-series airplanes. An NTSB database search from April 2006 to January 2015 found at least four other C-421 main landing gear collapses possibly attributable to pivot bolt failure. Since 2006, there were 32 additional accidents and 5 incidents involving landing gear problems on Cessna 300 or 400 series airplanes.
In response to the EC-IPO investigation, CIAIAC issued Safety Recommendation 11/08 to Cessna, recommending improved landing gear rigging guidance. Cessna made no changes. The FAA did not issue any advisory or corrective action regarding the pivot bolts, stating it did not perceive an airworthiness issue warranting an airworthiness directive. Transport Canada issued a Service Difficulty Advisory in March 2010 urging compliance with Cessna SIDs and service bulletins.
The NTSB determined that the maintenance provider, Pacific States Aviation, could not initially locate the relevant SIDs and CAIs in the Cesview system, even with Cesview support assistance. The documents were eventually found about two years after the accident with guidance from a Cessna air safety investigator.