A Lead Mechanic reports on the use of an alternate tool to measure AOA vane deflection against a fixed scale on a Challenger 601 to satisfy an airworthiness directive. Aircraft was grounded later; after alternate tool was considered not a manufacturer or AD approved tool.

Narrative

While performing an Angle of Attack (AOA) Transducer Resistance Inspection associated with Airworthiness Directive (AD) 2003-22-12; and Alternate Method of Compliance (AMOC) letter; dated March 2004; an alternate tool was used to measure AOA deflection against a fixed scale. Resistance values were measured at various degrees with no defects noted. All values were within allowable tolerances. The use of the alternate tool was thought to be acceptable based on Bombardier's Tooling Manual reference; allowing for the use of 'commercially' available equipment as long as the tool can be determined to meet; or exceed; operating tolerance of Bombardier's equipment. Once the alternate tool use was discovered; the aircraft was grounded until such time the tool referenced in the maintenance manual was procured and the test was accomplished. Results of the test with this tool were same as with the alternate tool. Mechanic was counseled about the use of the correct tool; even though Bombardier's Tooling Manual suggests the use of alternate tools if certain parameters are met. Aircraft scheduling might have played a role in mechanic's decision to use what he thought was an acceptable tool. The decision was made to never use alternate tools unless written authorization is obtained from aircraft manufacturer.