Introduction
On September 28, 2011, at 1715 eastern daylight time, a Mitsubishi MU-2B-25, registration N344KL, operated by Laurel Mountain Aviation LLC, sustained a nose landing gear collapse during the landing roll at Cobb County Airport-McCollum Field (RYY) in Atlanta, Georgia. The flight, conducted under 14 CFR Part 91, originated from Huntsville International Airport (HSV) in Alabama at 1541 central daylight time. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The airline transport rated pilot and two passengers reported no injuries. The airplane received structural damage to the nose and structure aft of the primary bulkhead.
Flight Details
The pilot reported that after departing HSV, he climbed to a cruise altitude of 11,000 feet mean sea level. Upon arrival near RYY, he was cleared for a visual approach to runway 27. After entering a right closed traffic pattern and completing all required checklist items, the airplane touched down. During the landing roll, the nose landing gear collapsed, and the airplane came to rest upright on the runway.
Maintenance Issues
Examination of the nose landing gear down lock installation revealed that the strut part number 010A-39117-11, installed on the right side of the trunnion, was installed incorrectly. The bearing stake marks should have been on the outboard side of the strut. Incorrect installation could allow the bearing to pull loose from the pin on the right side of the trunnion.
Maintenance records indicated recent work on the nose gear involving the strut. The design of the strut is typical for both left and right sides; both have the base part number 010A-39117, permanently marked by cast numbers on the outboard side. According to the manufacturer, the right strut should display part number 010A-39117-12 and the left -11. The manufacturer issued Service Bulletin No. 200B on June 24, 1994, addressing orientation and adjustment. The MU-2 Maintenance Manual did not address the installation or correct orientation of the strut. The service bulletin notes that the part number may be visible from the outboard sides and that inked part numbers may fade. The accident strut exhibited only the base number. The left strut was installed in accordance with the service bulletin.
The last annual and 200-hour inspection was conducted on July 11, 2011, 10 flight hours before the accident. The airplane was subsequently flown to a repair station for additional maintenance. The airplane had a previous nose landing gear failure and had been repaired by the pilot's mechanic. At the repair station, a mechanic observed only 2 millimeters of clearance in the nose landing gear down lock and informed the pilot that engagement was insufficient. The pilot instructed the mechanic to fix the problem, and the mechanic installed a short block part number 010A-39108-125 to achieve proper engagement per the maintenance manual. A review of logbooks could not determine who had previously worked on the drag strut.
Examination
The investigation focused on the incorrect installation of the strut as the cause of the collapse. The strut's orientation did not comply with manufacturer specifications, leading to inadequate retention of the bearing.