Operators of Hawker midsize business jets have been warned by the US Federal Aviation Administration that failure to maintain aileron control systems correctly could lead to wing and aileron oscillations that have the potential to cause structural fatigue.
In a special airworthiness information bulletin published on 27 November, the FAA revealed it has received reports of wing/aileron oscillations from operators of 800XP and 850XP business jets, at altitudes above 33,000ft (10,100m) and at speeds over Mach 0.73. “These oscillations were not divergent, and when airplane speed was reduced and the airplane was flown at an altitude below 30,000ft, the oscillations ceased,” says the FAA.
The agency says that further investigation revealed missing aileron bushings, low cable tension and improperly installed brackets, and that after the operators had corrected these faults according to the aircraft maintenance manual, “the oscillations did not recur”.
The FAA warns: “These oscillations could reduce the fatigue life of the aircraft, and in some severe cases could adversely affect the wing structure by causing the wing spars and stiffeners to crack. It is imperative that the wing structure be thoroughly checked after any such severe oscillations. The aileron and aileron tabs should also be checked to determine if the free play is within the limits recommended in the maintenance manual.”
The agency adds there is a risk that if instructions are not followed, the so-far harmless wing oscillations “could develop into divergent flutter, causing severe damage to the structure”. Although the fault has only shown itself on the Hawker 800XP and 850XP, the FAA recommends these checks should be carried out on all the types of the BAe 125-based business jet series, including the 750, 900XP, the 800 and 1000 families.