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The HSI drifted 25 degrees off heading causing the reporter to go off course on the bsr arrival to sfo. The controller canceled the approach clearance, and vectored the flight to a visual approach.
| Attributes | |
| ACN | 334750 |
| Time | |
| Date | 199604 |
| Day | Sun |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : sfo |
| State Reference | CA |
| Altitude | msl bound lower : 2000 msl bound upper : 10000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : oak |
| Operator | general aviation : personal |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Operating Under FAR Part | Part 91 |
| Navigation In Use | Other Other |
| Flight Phase | descent : approach descent other |
| Route In Use | arrival other arrival star : star |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument |
| Experience | flight time last 90 days : 90 flight time total : 1650 flight time type : 500 |
| ASRS Report | 334750 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe non adherence : clearance other spatial deviation |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
Coming into sfo on the bsr 1 arrival, we were descending out of 10000 ft to maintain 4000 ft and were cleared for the approach, when the captain noticed that the 2 HSI compasses disagreed by about 25 degrees. At about the same time the approach controller told us we were 3 mi left of course, canceled our approach clearance, and vectored us for the visual runway 28R. The 2 ehsi's are identical except for size, therefore, with no compass flag appearing to indicate that one had failed, it was next to impossible to tell which one was right and which was wrong. (Wet compass was useless due to descent and turbulence.) we have since had both remote directional gyros on the airplane replaced.
Original NASA ASRS Text
Title: THE HSI DRIFTED 25 DEGS OFF HDG CAUSING THE RPTR TO GO OFF COURSE ON THE BSR ARR TO SFO. THE CTLR CANCELED THE APCH CLRNC, AND VECTORED THE FLT TO A VISUAL APCH.
Narrative: COMING INTO SFO ON THE BSR 1 ARR, WE WERE DSNDING OUT OF 10000 FT TO MAINTAIN 4000 FT AND WERE CLRED FOR THE APCH, WHEN THE CAPT NOTICED THAT THE 2 HSI COMPASSES DISAGREED BY ABOUT 25 DEGS. AT ABOUT THE SAME TIME THE APCH CTLR TOLD US WE WERE 3 MI L OF COURSE, CANCELED OUR APCH CLRNC, AND VECTORED US FOR THE VISUAL RWY 28R. THE 2 EHSI'S ARE IDENTICAL EXCEPT FOR SIZE, THEREFORE, WITH NO COMPASS FLAG APPEARING TO INDICATE THAT ONE HAD FAILED, IT WAS NEXT TO IMPOSSIBLE TO TELL WHICH ONE WAS RIGHT AND WHICH WAS WRONG. (WET COMPASS WAS USELESS DUE TO DSCNT AND TURB.) WE HAVE SINCE HAD BOTH REMOTE DIRECTIONAL GYROS ON THE AIRPLANE REPLACED.
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.