MD-83
Flight Crew Air Transport Pilot (ATP)
Confusion; Distraction; Human-Machine Interface; Troubleshooting; Workload
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented; General Declared Emergency; General Maintenance Action
Aircraft
Descending approximately 15 miles east of destination through 6;000 MSL the A/P [Autopilot] and A/T [Autothrottles] disconnected. Master Caution 'Yaw Damp Inoperative' and 'Mach Trim Inoperative' messages illuminated on the EOAP [Electrical Overhead Annunciator Panel]. Both Nav Displays showed MAP FAIL and both Flight Directors went out of view. Both FMAs went to test mode and the A/P MCP went blank. The MCDUs showed GNS [Garmin Navigation System] FAIL. The Airspeed indicator and Altimeter appeared unaffected. Airspeed was later cross referenced with a request to ATC for indicated groundspeed and appeared to be consistent with what was presented on the instrument. No groundspeed was available on cockpit instruments. I took manual control of the aircraft while the First Officer searched the QRH for a relevant checklist. At this time ATC was giving vectors to avoid our destination's Class B airspace and as we had not yet verified that we had good heading information. Given the procedure for referencing the STBY Compass; I elected to declare an emergency. As we descended below the cloud bases; familiar landmarks were referenced and we were able to ascertain that we had good heading information from the RMIs. After a short discussion that it had to be coming from somewhere and given the lack of guidance from the QRH; we switched to DFGC [Digital Flight Guidance Computer] 2 and everything but the Captain's FD [Flight Director] started working. Placing the F/D selector switch to 'BOTH ON 2' gave F/D indications on the Captain's EADI [Electronic Attitude Direction Indicator]. We advised ATC that we had our instruments back and were vectored to the ILS. The approach and landing were uneventful. On the ground; reports were made to Local Maintenance and Dispatch. Messages were left with the Duty Pilot and Maintenance Control.
An MD-83 flight crew tangled with multiple Nav system failures as they descended near their destination. With assistance from ATC they were able to recover adequate navigation and attitude reference to complete their arrival.