N216WA

HISTORY OF FLIGHTOn May 1, 2013, about 1445 Pacific daylight time, a Cessna 421A, N216WA, sustained substantial damage as a result of a left main landing gear collapse during landing rollout at the Metropolitan Oakland International Airport (OAK), Oakland, California. The airline transport pilot and the pilot-rated owner were not injured. The personal flight was operated in accordance with 14 Code of Federal Regulations (CFR) Part 91. Visual meteorological conditions prevailed, and no Federal Aviation Administration (FAA) flight plan was filed for the local flight that had departed Buchanan Field (CCR), Concord, California, about 1330.

According to the pilot, earlier in the day, he had conducted several touch-and-go landings at CCR. In a second flight later that day, he and the airplane owner departed CCR, 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 OAK runway 27R, the pilot and the owner independently verified that the landing gear was extended by observing the landing gear position indicator lights. The touchdown was normal, but immediately thereafter, the left wing dropped, and then the airplane veered to the left. The airplane exited the left side of the runway, and came to rest upright. The pilot and owner exited the airplane, and observed that the left main landing gear (LMLG) had collapsed.

An FAA inspector examined the airplane shortly after the event. He reported that a bolt that functioned as the pivot axis for a landing gear extension and retraction component had failed, and that a LMLG bellcrank assembly that was part of the extension and retraction mechanism was also damaged. The bellcrank and bolt were retained for further examination. PERSONNEL INFORMATIONAccording to the pilot, he held an airline transport pilot certificate with multiple ratings. He reported that he had a total flight experience of approximately 6,720 hours, including about 200 hours in the accident airplane make and model. His most recent flight review was completed in October 2012, and his most recent FAA third-class medical certificate was also issued in October 2012. AIRCRAFT INFORMATIONFAA information indicated that the airplane was manufactured in 1969, and was equipped with two Continental Motors GTSIO-520 series engines. It was acquired by its current owner in October 2007. METEOROLOGICAL INFORMATIONThe OAK 1453 automated weather observation included wind from 310 degrees at 12 knots, visibility 10 miles, clear skies, temperature 26 degrees C, dew point 9 degrees C, and an altimeter setting of 30.02 inches of mercury. AIRPORT INFORMATIONFAA information indicated that the airplane was manufactured in 1969, and was equipped with two Continental Motors GTSIO-520 series engines. It was acquired by its current owner in October 2007. WRECKAGE AND IMPACT INFORMATIONThe airplane struck a taxiway sign, and came to rest off the left side of runway 27R. The gear collapse resulted in left engine propeller blade contact with the pavement, which damaged those blades. The left fuel tip tank and left wing, including the spar and aileron, incurred 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 that 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. Damage to the landing gear and airplane structure precluded the determination of the airplane's pre-accident landing gear rigging status. ADDITIONAL INFORMATIONLanding Gear Design

All three landing gear were extended and retracted by a single motor, which operated a series of push-pull rods and links. The main landing gear extended in the outboard direction, and each was locked in the extended position by an overcenter positioning of the side braces of its respective bellcrank assembly. Each aluminum bellcrank pivoted parallel to the airplane lateral axis on a steel bolt. Failure of the bellcrank pivot bolt would partially or completely free the bellcrank from its pivot, prevent the side brace from locking in its overcenter position, and permit landing gear collapse under certain loading conditions.

Cessna Landing Gear Maintenance Guidance

FAA regulations mandate that aircraft maintenance providers "shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable" to the FAA.

The Cessna 421 Service Manual (SM) is the document that contains the specific maintenance guidance for that model airplane. A "warning" appeared as a banner across the first page of the Landing Gear section of the C-421 SM. That warning stated "Anytime a landing gear retraction or extension system component has been removed, replaced or tension on the downlocks adjusted, the entire landing gear system must be re-rigged."

Cessna originally produced its maintenance guidance in hardcopy but transitioned to a computer-based system termed "Cesview." According to Cessna, Cesview was an application suite that enabled users "to view and manage electronic service and maintenance information manuals." Installation options permitted users to configure the system to their needs, from standalone (on DVD) to internet-based guidance. Users paid fees to obtain subscriptions, which ensured that they had access to the most current and complete information, including all updates and supplements.

Additional Cessna Landing Gear Maintenance Guidance

As a result of the in-service experience with the airplane, Cessna issued additional or supplemental maintenance-related guidance for the Cessna 421 or Series 300 and 400 airplanes.

In November 1993, Cessna issued Supplemental Inspection Document (SID) 32-10-03, applicable to all model 421 airplanes. It concerned inspection, and replacement depending on condition, of each main landing gear bellcrank pivot bolt. That SID specified an initial inspection at 1,000 landings or 3 years, whichever came first, and a repetitive cycle of 500 landings or 3 years.

In October 1999, Cessna issued revision 3 of the Continued Airworthiness Inspection (CAI) 32-10-03, applicable to most Series 400 airplanes, including all model 421 airplanes. The original issue date was unable to be determined. The CAI concerned inspection, and replacement depending on condition, of each main landing gear bellcrank pivot bolt. The CAI specified an initial inspection at 1,000 hours, and a repetitive cycle of 500 hours.

In June 2002, Cessna issued SID 32-30-05, applicable to all model 421 airplanes. That SID specified an initial "tear down and inspection" of the landing gear retraction system at 7,500 landings or 15 years, whichever came first, and a repetitive cycle of 5,000 landings or 10 years.

In addition to those three documents, Cessna issued at least an additional two CAI and two SID inspection documents regarding the Cessna 421 landing gear system.

There is no FAA requirement for aircraft in Part 91 operations to track number of landings; tracking an aircraft's number of landings is not the norm in Federal Aviation Regulations Part 91 operations, and the number of landings for the accident airplane was not tracked.

N216WA Maintenance Provider Information

According to the airplane owner, he almost exclusively utilized Pacific States Aviation (PSA), an FAA-certificated repair station at his home airport in California, for the maintenance and inspection of the airplane. PSA subscribed to Cesview to obtain the maintenance guidance specific to each airplane model. According to information provided by PSA, the airplane inspections were accomplished in accordance with the "PSA annual inspection checklist."

Within a few days of the accident, an FAA inspector visited the PSA facility to review their maintenance guidance for the airplane. The PSA maintenance manager and the FAA inspector were unable to locate or access the landing gear SIDs and CAIs in Cesview. They then telephoned Cesview support for assistance, but the Cesview representative was also unable to locate the documents, and was unable to explain why the guidance could not be located. About 2 years after the accident, in response to separate requests of the FAA inspector and the NTSB investigator, the PSA maintenance manager twice again was unable to locate the SID and CAI. Subsequent to that, the Cessna air safety investigator personally guided the maintenance manager through the search process, and the manager was able to access the documents. The reasons for the previous inability of Cesview support to successfully guide the PSA maintenance manager were not determined.

Other Maintenance Provider Information

A representative of one maintenance provider familiar with the Cessna 421 reported that the Cessna-published rigging process is time-consuming complex, with some "gray areas." He stated that a technician who is familiar with the process would typically require 6 to 8 hours per gear leg to accomplish a complete re-rig of the landing gear system, and that a significant portion of that effort would require a second technician. An operator whose fleet included model 402 airplanes, but not any model 421 airplanes, reported that the bellcrank pivot bolt was not part of the model 402 landing gear configuration. However, that operator reported that it had to reduce Cessna-recommended maintenance intervals on some landing gear components due to its in-service experience.

N216WA Landing Gear Maintenance Information

In June 2006, the airplane experienced a LMLG collapse on landing. The pivot bolt had failed, but the damage was minor, and the event was not categorized as an accident by the NTSB. At the time of that event...