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A B737-400 experienced a transponder anomaly that indicated a climb when the aircraft was descending to a cleared altitude.
| Attributes | |
| ACN | 636857 |
| Time | |
| Date | 200411 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | airport : clt.airport |
| State Reference | NC |
| Altitude | msl bound lower : 29000 msl bound upper : 31000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B737-400 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : vacating altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi pilot : multi engine pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 29000 flight time type : 12000 |
| ASRS Report | 636857 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : less severe other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | flight crew : overcame equipment problem |
| Consequence | other |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
Cleared to FL290 from FL310. We read back the clearance correctly and confirmed the proper target altitude on the mode control panel. Shortly thereafter, we were asked if we could be at FL290 within 2 mins. We replied affirmative. The controller then asked what our altitude was, and if we had climbed instead of descended. There was some confusion with ATC, presumably because of a mode C anomaly. We switched xponders, and leveled at FL290 within approximately 1 min. There was no traffic conflict. The flight continued normally, and the transponder was reported to maintenance.
Original NASA ASRS Text
Title: A B737-400 EXPERIENCED A XPONDER ANOMALY THAT INDICATED A CLB WHEN THE ACFT WAS DSNDING TO A CLRED ALT.
Narrative: CLRED TO FL290 FROM FL310. WE READ BACK THE CLRNC CORRECTLY AND CONFIRMED THE PROPER TARGET ALT ON THE MODE CTL PANEL. SHORTLY THEREAFTER, WE WERE ASKED IF WE COULD BE AT FL290 WITHIN 2 MINS. WE REPLIED AFFIRMATIVE. THE CTLR THEN ASKED WHAT OUR ALT WAS, AND IF WE HAD CLBED INSTEAD OF DSNDED. THERE WAS SOME CONFUSION WITH ATC, PRESUMABLY BECAUSE OF A MODE C ANOMALY. WE SWITCHED XPONDERS, AND LEVELED AT FL290 WITHIN APPROX 1 MIN. THERE WAS NO TFC CONFLICT. THE FLT CONTINUED NORMALLY, AND THE XPONDER WAS RPTED TO MAINT.
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.