MD-82
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Workload; Distraction; Situational Awareness
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft; Procedure
We departed the gate late because of the airplane having a maintenance write up on the compass system. Maintenance did replace a part in the gyro compass system and signed off the logbook. During taxi out; all gyro compass indications looked normal. After take off and climbing through about 16;000 FT the heading annunciator on both FMAs illuminated; the Flight Director failed; and the autopilot tripped off. During this time we went through assigned altitude of 25;000 FT by about 200 FT. We advised ATC that we were returning to the departure airport. At times there was a 40 degree split between the two compass systems. Because of the heading issues; we declared an emergency and landed with out incident. This event was caused due to the gyro compass system failure.
A MD82 crew discovered after the FMA annunciated HEADING that the compass headings were up 40 degrees different; so an emergency was declared and the flight returned to the departure airport where maintenance on the compass had previously been performed.