Narrative:

While in descent from 11;000 to 8;000 ft we received a heading annunciation on the FMA comparator panel; both captains and first officers heading looked alike but checking them with the stby compass we were 45 degrees off magnetic heading. At this time the controller was vectoring us to the ILS final. Attempted to slew headings closer to stby heading and advised the ATC controller of diminished navigation capability since our heading system was reading erroneously. The controller continued to issue us numerous heading assignments and traffic information on traffic ahead of us on the approach. We advised the controller that the field was in sight but he continued with heading and traffic advisories. While approximately 18 DME on final I declared an emergency with the controller again advising him of the heading system malfunction; really to gain traffic priority and to stop issuing heading assignments which we were unable to follow. Fortunately for us it was severe VFR and traffic and identifying the airport were never a problem. At about 14 DME the #1 and #2 transponder data bus annunciated on the TCAS screen telling us the transponder was not working properly; we advised the controller who acknowledged it and finally cleared us for the visual approach. Remainder of approach and landing were uneventful and wrote up discrepancies at the gate.

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Original NASA ASRS Text

Title: MD80 flight crew experiences a dual compass system failure during approach. An emergency is declared with the runway in sight and a normal landing ensues. During the approach both transponders also fail.

Narrative: While in descent from 11;000 to 8;000 FT we received a heading annunciation on the FMA Comparator Panel; both Captains and First Officers heading looked alike but checking them with the STBY compass we were 45 degrees off magnetic heading. At this time the Controller was vectoring us to the ILS final. Attempted to slew headings closer to STBY heading and advised the ATC Controller of diminished navigation capability since our heading system was reading erroneously. The Controller continued to issue us numerous heading assignments and traffic information on traffic ahead of us on the approach. We advised the Controller that the field was in sight but he continued with heading and traffic advisories. While approximately 18 DME on final I declared an emergency with the Controller again advising him of the heading system malfunction; really to gain traffic priority and to stop issuing heading assignments which we were unable to follow. Fortunately for us it was severe VFR and traffic and identifying the airport were never a problem. At about 14 DME the #1 and #2 Transponder Data Bus annunciated on the TCAS screen telling us the transponder was not working properly; we advised the Controller who acknowledged it and finally cleared us for the visual approach. Remainder of approach and landing were uneventful and wrote up discrepancies at the gate.

Data retrieved from NASA's ASRS site as of April 2012 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.