AL 1999-05
9 December 1999
Control Column Bobweight Support Cracks
While complying with a Phase 5 Inspection on a Citation II aircraft, maintenance personnel performing a control column inspection noticed cracks on the control column bobweight supports (P/N 5565550-26). The maintenance organization submitted a Service Difficulty Report (SDR) that stated both left and right supports had cracks near the aft (torque tube) end. The submitter stated that the cracks started in the upper flange of the support and extended into the web area approximately one inch from the aft end, on the upper edge of the support. The parts were not made available to Transport Canada for inspection or analysis. At the time there were no other reported instances of this problem. Subsequently, the maintenance organization that submitted the first SDR discovered a similar crack in another 550, which was undergoing a Phase 5 inspection also. Both aircraft had accumulated approximately 3600 hours TSN and 4100 landings.
Fatigue stress damage to the balance weight supports may occur by slamming the control column forward during cockpit entry or egress, certain control column maintenance procedures, or subjecting the aircraft to wind, jet or rotor blasts while parked on a ramp area without engaging the control locks.
According to the illustrated parts catalogues for the 500, 501 and the S550, these aircraft all have similar bobweights installed. While the 500 and 501 use the same part number support, the S550 has two bobweights installed and uses different part number supports.
Both the 500/501 and the 550 maintenance manuals specify a check of the bobweight assembly, while inspecting the control column (inspection item code number A273009 for the 500/501 and A273005 for the 550) at each Phase 5 inspection. The inspection item for the S550 (code number A273007) does not, however, mention the two bobweights specifically.
Although Transport Canada is unaware of an instance of failure of this part, the potential exists for a damaged bobweight support to interfere with the operation of the elevator control system. Transport Canada recommends that at the next access to the affected parts, or the next primary phased inspection (whichever comes first), particular attention is paid to inspection of the bobweight support arms.
Any defects in the bobweight assembly found during an inspection performed as a result of this advisory or other scheduled or unscheduled maintenance, should be reported by sending an SDR to Transport Canada, Continuing Airworthiness, Ottawa.
For further information contact a Transport Canada Centre, or Mr. Mark Stephenson, Continuing Airworthiness, Ottawa, telephone (613) 952-4363, fascimile (613) 996-9178 or e-mail stephma@tc.gc.ca.
For Director, National Aircraft Certification
B. Goyaniuk
Chief, Continuing Airworthiness