Spectrum LLC 33, a proto-type experimental twin engine, carbon fibre construction, executive jet aircraft. The aircraft was issued a special airworthiness certificate in the experimental category for the purpose of research and development by the FAA on November 7, 2005. The aircraft had flown approximately 44 hours total flight time since its first flight on January 7, 2006.
On 25 July 2006 the aircraft was taking off from Spanish Fork City Airport, Utah, USA when the airplane rolled right almost immediately after liftoff. The roll continued until the aircraft was banked at 90 degrees right wing down, at which point the right wingtip impacted the ground. The plane did not catch fire but tragically both pilots died from the impact. No flight plan was filed for the 14 CFR Part 91 local maintenance test flight.
Prior to the flight the aircraft had undergone maintenance that required the Main Landing Gear (MLG) struts to be stiffened. This maintenance action was carried out successfully but upon reinstallation of the struts it was discovered that the stiffened MLG impacted on a V bracket which held the aileron control systems upper torque tube. To solve the issue created by the stiffened struts the V bracket was removed and redesigned. The work associated with this required the removal of the aft upper torque tube bell crank from the torque tube. The subsequent reinstallation of the bell crank on the torque tube was done incorrectly. The mechanic who did the job assumed that there was only one way to fit the bell crank when in fact there where two. As a result of the incorrect installation of the bell crank, binding in the aileron system was discovered. Unfortunately the incorrectly installed bell crank was not discovered, so to fix the binding issue aileron tie rods and the upper torque tube were altered. This alteration now meant that the aileron system worked in reverse. Surprisingly at this stage of maintenance, no aileron system check was carried out to check control surface movement against flight control movement. Confounding the fact that the check was not completed is the fact that due to the aircraft being a proof-of-concept aircraft no maintenance documentation to instruct mechanics how to perform or document the work existed. Had a system check been undertaken either by the maintenance mechanic post working on the system or by the flight crew during the pre-flight checks, the aileron rigging error would have been picked up.
Human Factor Points
- Mechanic assumed that there was only one way to fit the bell crank. There is no place for assumptions within aviation.
- No maintenance documentation used for task. Company maintenance managers should have been more vigilant and ensured their mechanics had the appropriate documentation for the job.
- There were two opportunities to have the aileron system checked for correct operation, the maintenance check was not undertaken and the flight crew pre-flight check did not pickup the fault. The NTSB report also found that there were two pre-flight checklists in the flight deck. One checklist dated 25 July 2006 included the item "Flight Controls - CHECK" in both the Pre-Start and the Before Takeoff sections of the checklist. The other checklist dated 17 April 2006 included the items "Control Locks - REMOVED" and "Flight Controls - CHECKED" in the Pre-Start section of the checklist and the item "Gust Locks/Controls - OFF/CHECKED" in the Before Takeoff section of the checklist.
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