History of Flight
On October 21, 2009, about 1015 mountain daylight time, an Aero Commander 690, registration N690TR, operated by Kolab Canyon Air Services, LLC, experienced the collapse of its right main landing gear during landing rollout at Cedar City Regional Airport (CDC), Cedar City, Utah. The airplane was on a positioning flight to pick up passengers in Milford, Utah. Visual meteorological conditions prevailed, and a company flight plan had been filed. The airplane sustained substantial damage, and the commercial pilot was not injured. The flight was conducted under 14 Code of Federal Regulations Part 91 and had originated from CDC about 0709.
The pilot reported to the National Transportation Safety Board investigator that he attempted to lower the landing gear on approach to Milford Municipal Airport. The nose gear and left main landing gear locked down, but the right main landing gear did not fully extend. The pilot performed emergency procedures from the airplane's flight manual, but the right landing gear failed to lock down. He then flew back to CDC and landed.
During rollout, the right main landing gear collapsed. As the airplane decelerated, it slid off the runway and came to rest in an adjacent dirt area. Examination of the airplane revealed several bent bulkheads and stringers.
Examination and Testing
The operator reported maintaining the airplane using the manufacturer's approved inspection program. No anomalies, including preexisting damage, were reported with the landing gear extension system.
Following the accident, the landing gear operating system was examined. Two components associated with the gear extension system were bench tested: the accumulator/regulator (part number EA1563) and the priority valve (part number 2979-3 (790301-501)). Both did not meet specifications. When the accumulator/regulator was serviced with nitrogen to the specified test pressure, it would not pressurize. When the priority valve was pressurized, it operated only below specified limits for its part number.
According to the Federal Aviation Administration (FAA) coordinator, the inability of the accumulator/regulator to be pressurized resulted in the landing gear's failure to properly extend. Additionally, the priority valve installed in the airplane was an incorrect part. Twin Commander's technical service manager reported that the correct priority valve part number was 790301-505. The installation of the improper valve "...most likely contributed to the failure of the landing gear to fully extend to the down and locked position."