History of the Flight
On 9 December 2010 at 1021 hrs, a Cessna 750 Citation X, registration G-CDCX, was positioning from Luton to Doncaster Airport for minor preventative maintenance. The weather was good, and the flight was described as normal. The aircraft was radar vectored onto an ILS approach for Runway 20. The autopilot was disengaged at five miles, and the commander flew the approach manually. The surface wind was reported by ATC as 290° at 11 kt, within the aircraft's crosswind limit.
Pilots described the approach and flare as normal. The landing was to the left of the runway centreline and within the instrument landing area, described as smooth, though the commander recalled the right main landing gear (MLG) touched down slightly before the left. As the nose began to drop, the aircraft rolled gently to the right and a judder was felt through the control yoke. The commander quickly realized a landing gear problem and attempted to keep the aircraft straight using left brake and rudder. The co-pilot advised ATC of the problem and shut down the engines. As speed decreased, directional control was lost and the aircraft veered right, coming to a halt on the edge of the runway. The crew shut down remaining systems and vacated normally.
ATC observed what appeared to be a normal landing, then saw sparks from the right side and a wheel bouncing down the runway. They initiated crash procedures; the fire service responded immediately, reaching the aircraft seconds after it stopped. Considerable debris, including both right mainwheels, was found on the runway.
Aircraft and Crew Information
The aircraft was a Cessna 750 Citation X, manufactured in 2002, with two Rolls-Royce AE 3007C1 turbofan engines. The commander held an Airline Transport Pilot's Licence, aged 34, with 4,800 hours total flying experience (600 on type). The co-pilot was also on board; there were no passengers. Both crew members reported no injuries.
Examination of the Aircraft
The aircraft came to rest just off the paved surface to the right of the runway, having turned about 45° to the right. The ground was frozen hard. The aircraft rested on its right wingtip, flaps, and the remains of the MLG vertical cylinder, which had been partially ground away by runway contact. A small puncture of the right elevator was also noted.
Runway marks showed twin gouges from the trunnion forks, becoming a broader single scrape as the forks wore down. The commencement of gouges was about one metre left of the runway centreline, indicating left displacement on touchdown, but this was not considered to have bearing on the failure. Debris along the slide path included the two mainwheels, most of the fractured trailing link, and the shock absorber oleo strut.
Examination of the Landing Gear
The MLG was a trailing link design (part number 6741013-3). The link was made from 300M ultra-high tensile strength steel, shot-peened, grit-blasted, cadmium plated, and painted. Examinations revealed a circumferential fracture at the forward end of the trailing link, with a longitudinal crack running 27 cm along the upper surface. A darker area at the intersection of these fractures suggested the crack pre-existed the final fracture and caused an overload failure.
The failed link was sectioned longitudinally. Extensive corrosion and loose paint were found on the upper surface near the knee, while the lower half appeared crack-free with no paint loss but a black stain indicating long-term liquid pooling. The crack originated just forward of the knee on the inner surface, propagating forward and aft simultaneously until reaching about 275 mm, at which point instantaneous rupture occurred. Scanning Electron Microscope examination confirmed the crack propagated through stress corrosion cracking (SCC). Surface corrosion was severe, with pitting.
Probable Cause
The trailing link failed due to a pre-existing stress corrosion crack, leading to detachment of the right mainwheels.