Beech 1900
Time Pressure; Confusion; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Less Severe
General Flight Cancelled / Delayed; General Maintenance Action
Human Factors; MEL; Procedure
The [flight] crew found the Number 1 Yaw Damper Computer to be inoperative and wrote it up upon landing from Flight ABCA. Mechanic X came to MEL and signed-off the write-up. He referenced the 'O' Procedures and chose to pull the Circuit Breaker (C/B) and collar it. He discussed this with the crew and we agreed that the MEL was unclear and confusing; and the most conservative action was to follow that 'O' Procedure.  However; Supervisor for Mechanic X; told Mechanic X that common sense dictated that the 'O' Procedure need not be followed because the MEL allows for one Yaw Damper Computer to be 'inoperative' if the other is 'operative.'  So Mechanic X was instructed to remove the collar and reset the Circuit Breaker.  Because MEL 22-2-2 refers to two scenarios and the 'O' Procedure did not describe which scenario it applied to; we were not sure what was legally binding. So we called Chief Pilot to clarify the situation. She agreed with the common sense argument; so to avoid further delay; we continued. The MEL did state one Yaw Damper Computer 'may be inoperative; provided the operative computer is selected.' And the MEL indicated that two computers were installed and only one was required for flight.  We contacted our Dispatcher for a new Aircraft Release with the MEL added. He understood our confusion; and agreed with the solution. We asked him to clarify the wording on the release so it indicated only one Yaw Damper Computer was inoperative.  Our recommendation is that MEL 22-2-2 be revised.One suggestion would be to divide MEL 22-2-2 into: MEL 22-2-2-a) and MEL 22-2-2-b). MEL 22-2-2-a) should say 'One may be inoperative provided the operative computer is selected. MEL 22-2-2-b) should say 'Both may be inoperative.'Another suggestion is for the 'O' Procedure be numbered MEL 22-2-2-b); this would clarify which scenario the 'O' Procedure applies to. An 'O' Procedure could be added for MEL 22-2-2-a) to instruct the crew to insure the other Yaw Damper Computer is installed and 'Operative'. Part 121.
A pilot recommends a revision to the Beech 1900-D MEL 22-2-2 'Yaw Damper Computer;' to clarify as to 'when' an 'O' Procedure for pulling and collaring the Yaw Damper Computer Circuit Breaker (C/B) should apply.