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Turbo commander 690 aircraft was showing 1000 ft low, flight crew notified by approach controller. Transponder switched to #2 which appeared fine. Postflt inspection found no problem with the #1.
| Attributes | |
| ACN | 395947 |
| Time | |
| Date | 199803 |
| Day | Mon |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : bhm |
| State Reference | AL |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : bhm |
| Operator | general aviation : corporate |
| Make Model Name | Turbo Commander 690C |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other descent : approach |
| Route In Use | enroute airway : bhm enroute other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : instrument pilot : atp |
| Experience | flight time total : 4000 |
| ASRS Report | 395947 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : commercial |
| Events | |
| Anomaly | aircraft equipment problem : less severe other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
The approach control at bhm showed me to be exactly 1000 ft less than what I was flying. I checked both altimeters and verified both altimeter settings. We tried switching to #2 transponder but there was not enough time for it to warm up before landing. On the 2ND leg of the flight, we used #2 transponder, which seemed to work correctly and had our #1 checked after the flight. However, it showed no problems. I have seen altitude discrepancies before, but usually only 100 or 200 ft and never exactly 1000 ft. If you can shed some light on the possible cause of this event, please give me a call.
Original NASA ASRS Text
Title: TURBO COMMANDER 690 ACFT WAS SHOWING 1000 FT LOW, FLC NOTIFIED BY APCH CTLR. XPONDER SWITCHED TO #2 WHICH APPEARED FINE. POSTFLT INSPECTION FOUND NO PROB WITH THE #1.
Narrative: THE APCH CTL AT BHM SHOWED ME TO BE EXACTLY 1000 FT LESS THAN WHAT I WAS FLYING. I CHKED BOTH ALTIMETERS AND VERIFIED BOTH ALTIMETER SETTINGS. WE TRIED SWITCHING TO #2 XPONDER BUT THERE WAS NOT ENOUGH TIME FOR IT TO WARM UP BEFORE LNDG. ON THE 2ND LEG OF THE FLT, WE USED #2 XPONDER, WHICH SEEMED TO WORK CORRECTLY AND HAD OUR #1 CHKED AFTER THE FLT. HOWEVER, IT SHOWED NO PROBS. I HAVE SEEN ALT DISCREPANCIES BEFORE, BUT USUALLY ONLY 100 OR 200 FT AND NEVER EXACTLY 1000 FT. IF YOU CAN SHED SOME LIGHT ON THE POSSIBLE CAUSE OF THIS EVENT, PLEASE GIVE ME A CALL.
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.