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An air carrier crew discovers their compass system to be unreliable. With ATC assistance, a normal arrival is completed as WX improves.
| Attributes | |
| ACN | 571637 |
| Time | |
| Date | 200301 |
| Day | Sat |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : djb.vortac |
| State Reference | OH |
| Environment | |
| Flight Conditions | IMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zob.artcc tracon : d21.tracon tower : smf.tower |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : commercial pilot : flight engineer pilot : atp pilot : cfi |
| Experience | flight time last 90 days : 100 flight time total : 16000 flight time type : 3000 |
| ASRS Report | 571637 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : critical other anomaly other |
| Independent Detector | other flight crewa other flight crewb |
| Resolutory Action | flight crew : diverted to alternate flight crew : overrode automation |
| Consequence | other other |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
Flight from rdu to dtw. On climb out, observed 7-15 degree difference between captain and first officer compass system. Crosschecked standby compass and first officer's system seemed ok. Captain's system off. First officer compass system. Drives captain HSI so no problem flying aircraft. Heading difference fluctuated zero-20 degrees out in climb and cruise. Approximately 100 NM east of djb, cle center gave direct to djb. In turn, we observed first officer HSI (captain's RMI) locked up, then jumped left while in a right turn. Captain RMI (first officer HSI) froze on a 315 degree heading. Captain HSI read 290 degrees, but standby compass showed 220 degrees. We advised cle of unreliable compass system and requested gyro out procedures. Contacted our airline dispatch and maintenance control on communication #2 to advise of problem. Dtw had been 2000 ft overcast 1 1/2 snow. Cmh was 6000 ft overcast 10 mi visibility. Dispatch advised that dtw was improving -- 4000 ft overcast 4 mi visibility, also dtw approach agreed to take us on gyro out. We agreed to continue to dtw for 1 attempt. Then missed approach to cmh (already our alternate, fuel on board was more than sufficient). Dtw was 6000 ft overcast 10 mi visibility by then, and approach was uneventful. Excellent cooperation and coordination by cle ATC and dtw approach allowed us to complete the scheduled flight safely. Aircraft was written up and grounded in dtw. Callback conversation with reporter revealed the following information: the aircraft was taken out of service. It had a previous history of similar problems that resulted in maintenance replacing some wiring and ferrous rivets and screws near the right flux valve. This flux valve was replaced after this incident, and the aircraft released for service. Similar problems continued to occur for the next month when technical specialists were called in to demagnetize or replace more rivets. Problems continued until it was found that the left flux valve was out of adjustment. At the time of the callback, this appears to be the final fix.
Original NASA ASRS Text
Title: AN ACR CREW DISCOVERS THEIR COMPASS SYS TO BE UNRELIABLE. WITH ATC ASSISTANCE, A NORMAL ARR IS COMPLETED AS WX IMPROVES.
Narrative: FLT FROM RDU TO DTW. ON CLBOUT, OBSERVED 7-15 DEG DIFFERENCE BTWN CAPT AND FO COMPASS SYS. XCHKED STANDBY COMPASS AND FO'S SYS SEEMED OK. CAPT'S SYS OFF. FO COMPASS SYS. DRIVES CAPT HSI SO NO PROB FLYING ACFT. HDG DIFFERENCE FLUCTUATED ZERO-20 DEGS OUT IN CLB AND CRUISE. APPROX 100 NM E OF DJB, CLE CTR GAVE DIRECT TO DJB. IN TURN, WE OBSERVED FO HSI (CAPT'S RMI) LOCKED UP, THEN JUMPED L WHILE IN A R TURN. CAPT RMI (FO HSI) FROZE ON A 315 DEG HDG. CAPT HSI READ 290 DEGS, BUT STANDBY COMPASS SHOWED 220 DEGS. WE ADVISED CLE OF UNRELIABLE COMPASS SYS AND REQUESTED GYRO OUT PROCS. CONTACTED OUR AIRLINE DISPATCH AND MAINT CTL ON COM #2 TO ADVISE OF PROB. DTW HAD BEEN 2000 FT OVCST 1 1/2 SNOW. CMH WAS 6000 FT OVCST 10 MI VISIBILITY. DISPATCH ADVISED THAT DTW WAS IMPROVING -- 4000 FT OVCST 4 MI VISIBILITY, ALSO DTW APCH AGREED TO TAKE US ON GYRO OUT. WE AGREED TO CONTINUE TO DTW FOR 1 ATTEMPT. THEN MISSED APCH TO CMH (ALREADY OUR ALTERNATE, FUEL ON BOARD WAS MORE THAN SUFFICIENT). DTW WAS 6000 FT OVCST 10 MI VISIBILITY BY THEN, AND APCH WAS UNEVENTFUL. EXCELLENT COOPERATION AND COORD BY CLE ATC AND DTW APCH ALLOWED US TO COMPLETE THE SCHEDULED FLT SAFELY. ACFT WAS WRITTEN UP AND GNDED IN DTW. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT WAS TAKEN OUT OF SVC. IT HAD A PREVIOUS HISTORY OF SIMILAR PROBS THAT RESULTED IN MAINT REPLACING SOME WIRING AND FERROUS RIVETS AND SCREWS NEAR THE R FLUX VALVE. THIS FLUX VALVE WAS REPLACED AFTER THIS INCIDENT, AND THE ACFT RELEASED FOR SVC. SIMILAR PROBS CONTINUED TO OCCUR FOR THE NEXT MONTH WHEN TECHNICAL SPECIALISTS WERE CALLED IN TO DEMAGNETIZE OR REPLACE MORE RIVETS. PROBS CONTINUED UNTIL IT WAS FOUND THAT THE L FLUX VALVE WAS OUT OF ADJUSTMENT. AT THE TIME OF THE CALLBACK, THIS APPEARS TO BE THE FINAL FIX.
Data retrieved from NASA's ASRS site as of July 2007 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.