Bombardier Q100/200/300 - Service Difficulty Alert

AL 2006-04
18 September 2006

Overhaul of Flap Actuators

Operators of Bombardier Q100/200/300 aircraft have been complying with Alert Service Bulletin A8 27-98, which is mandated by Canadian Airworthiness Directive CF-2002-26R1, which requires a decreasing backlash inspection interval as the flap track actuator backlash increases. These repetitive backlash inspections ensure that a maximum backlash limit of 0.070" is not exceeded. 

Recently Bombardier Aerospace has issued an All Operators Message (AOM) 811, in which they identify the results of an investigation into several overhauled actuators that exhibited high wear rates. It was determined that some overhaul facilities may have been identifying the actuator as « Overhauled », without replacing the ball screw and nut assemblies.

According to Canadian Airworthiness Directive CF 2002 26R1, an « Overhauled » actuator does not need to be checked for backlash until 3000 hours in service following the « Overhaul ». If the ball screw and nut assembly have not been replaced, there is a concern that existing and accelerated wear could result in the maximum backlash limit of 0.070" being exceeded within the 3000 hours in service before the next scheduled backlash check, with the subsequent possibility of premature failure of the actuator.

The investigation has also resulted in Hamilton Sundstrand (OEM) revising the flap actuator component maintenance manual (CMM) to prohibit any future overhaul or repair of the ball screw and nut assembly. Every actuator that is certified as « Overhauled » must now have the ball screw and nut assembly replaced with a new assembly as part of the overhaul. If the ball screw and nut assembly has not been replaced, the actuator should not be identified as « Overhauled » but only identified as « Repaired ».

In addition, references to the Beaver Precision Products CMM 27-50-12, which had been included as appendices to the Hamilton Sundstrand CMM, have been removed and are no longer valid. Operators should ensure that the overhaul facility to which they send the actuator for overhaul, utilizes the current Hamilton Sundstrand CMM, and that any copies of the Beaver CMM are not utilized..

Transport Canada strongly recommends operators and overhaul facilities affected by the content of this Service Difficulty Alert, review the records of installed and spare flap actuators to determine their overhaul condition, in accordance with the latest Hamilton Sundstrand CMM. If it cannot be verified that the ball screw and nut assembly were replaced as part of the overhaul, the actuator is to be considered as suspect.

It is recommended that two such suspect actuators should not be installed on the same flap panel. It is also recommended that operators should be particularly vigilant for any signs of excessive flap actuator wear and should consider reducing the interval between backlash checks for these suspect actuators to establish the wear rate.

Similar defects or further occurrences of this nature are to be reported to Transport Canada, Continuing Airworthiness, Ottawa, via the Service Difficulty Reporting program.

For further information contact a Transport Canada Center, or Mr. Marcel Gauthier, Continuing Airworthiness, Ottawa, telephone 613-952-4364, facsimile 613-996-9178 or e-mail

For Director, National Aircraft Certification

A. Wan
Acting Chief, Continuing Airworthiness

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