Narrative:

During originating checks; it was discovered that all lateral and vertical guidance buttons on the flight guidance control panel (fgcp) would not engage. Additionally; the yaw damp buttons would not engage. As a part of the write up process; the captain entered these separate line items in the aircraft maintenance record and conferred with maintenance control who advised that MEL 22-1 (autopilot) could be applied to both items. The MEL procedure was completed and the flight was operated using raw data. After further reflection; the crew determined the following:1 - the inoperative yaw damp line item should have been MEL'd using 22-4(b) yaw damper channels - both inoperative.2 - based on the inoperability of the left/right automated flight control system (afcs) control button; the underlying problem may have been the flight guidance computers (FGC). Had this been the case; the aircraft should not have been dispatched as one of the two FGC must be operative per MEL 22-6(a) flight guidance computers.as to the first determination (yd channels); the PIC; in conjunction with maintenance control should not have applied the autopilot MEL (22-1) as an all-encompassing MEL. Further exploration of possible mels should have been accomplished as to apply the correct MEL.the application of MEL (22-1) was largely predicated on the use of the same MEL the previous day. Accurate repair of inoperative items; aside; a recurring write up should have directed both the PIC and maintenance control to consider related systems further. Per the preamble of the MEL book; the interrelationships between multiple inoperative items should be considered to ensure an acceptable level of safety is maintained. Again; further reflection on the part of the PIC should have caused consideration of the flight guidance computers as the underlying problem. Perhaps a note; as appears in MEL 22-4; could be inserted into MEL 22-1 drawing attention to the need to confirm operation of the at least one of the fgcs.

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Original NASA ASRS Text

Title: The flight crew of a De Havilland Canada DHC-8-200 reported that maintenance authorized the deferral of the autopilot when both of the flight guidance computers were inoperative; which would make this an illegal deferral.

Narrative: During originating checks; it was discovered that all lateral and vertical guidance buttons on the Flight Guidance Control Panel (FGCP) would not engage. Additionally; the yaw damp buttons would not engage. As a part of the write up process; the Captain entered these separate line items in the aircraft maintenance record and conferred with Maintenance Control who advised that MEL 22-1 (Autopilot) could be applied to both items. The MEL procedure was completed and the flight was operated using raw data. After further reflection; the crew determined the following:1 - The inoperative yaw damp line item should have been MEL'd using 22-4(b) Yaw Damper Channels - both inoperative.2 - Based on the inoperability of the left/right Automated Flight Control System (AFCS) control button; the underlying problem may have been the Flight Guidance Computers (FGC). Had this been the case; the aircraft should not have been dispatched as one of the two FGC must be operative per MEL 22-6(a) Flight Guidance Computers.As to the first determination (YD Channels); the PIC; in conjunction with Maintenance Control should not have applied the Autopilot MEL (22-1) as an all-encompassing MEL. Further exploration of possible MELs should have been accomplished as to apply the correct MEL.The application of MEL (22-1) was largely predicated on the use of the same MEL the previous day. Accurate repair of inoperative items; aside; a recurring write up should have directed both the PIC and Maintenance Control to consider related systems further. Per the preamble of the MEL book; the interrelationships between multiple inoperative items should be considered to ensure an acceptable level of safety is maintained. Again; further reflection on the part of the PIC should have caused consideration of the Flight Guidance Computers as the underlying problem. Perhaps a note; as appears in MEL 22-4; could be inserted into MEL 22-1 drawing attention to the need to confirm operation of the at least one of the FGCs.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.