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B737-200 crew had the ZTL controller tell them that the radar altitude readout on the radar scope showed an incorrect aircraft altitude.
| Attributes | |
| ACN | 514839 |
| Time | |
| Date | 200106 |
| Day | Tue |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : ztl.artcc |
| State Reference | SC |
| Altitude | msl single value : 35000 |
| Environment | |
| Light | Dusk |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B737-200 |
| Operating Under FAR Part | Part 121 |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 14000 flight time type : 10000 |
| ASRS Report | 514839 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | other anomaly other |
| Independent Detector | atc equipment other atc equipment : radar other other : 5 |
| Resolutory Action | none taken : anomaly accepted none taken : unable |
| Supplementary | |
| Problem Areas | ATC Human Performance ATC Facility |
| Primary Problem | Ambiguous |
Narrative:
Normal climb to FL350, bwi direct atl. After being level at FL350 for some time, the ZTL controller asked us our altitude. Replied level FL350. She then asked altimeter setting. Replied 29.92. She said she had us below FL350 (forget the exact altitude she said). We confirmed again we were level at FL350 with 29.92. We then switched modes on the mode C reporting, went to standby on the transponder, and checked all system -- to no avail. She now had us level at FL310, yet we were still at FL350. She tried for quite some time to get another aircraft (air carrier Y, B737) to see if they could see us, but we had no other aircraft on our TCASII close to us. In addition, we had a normal climb to FL350 and were on top of a cloud system about 1000 ft below us. An additional confusing problem was the fact that the controller kept calling us by the #XXXA instead of #XXXB. We tried several times to correct her. After quite a while of her talking to others, we lost her voice coverage and called in the blind for another frequency -- which we got, but we were never xferred. We don't know if she mixed up aircraft with call signs that were similar or not. On our descent, we got accurate mode C reports from every controller after her -- no indication of failure of degradation in the mode C at all, nor on the succeeding flight where we had repeated checks done all the way up to FL330.
Original NASA ASRS Text
Title: B737-200 CREW HAD THE ZTL CTLR TELL THEM THAT THE RADAR ALT READOUT ON THE RADAR SCOPE SHOWED AN INCORRECT ACFT ALT.
Narrative: NORMAL CLB TO FL350, BWI DIRECT ATL. AFTER BEING LEVEL AT FL350 FOR SOME TIME, THE ZTL CTLR ASKED US OUR ALT. REPLIED LEVEL FL350. SHE THEN ASKED ALTIMETER SETTING. REPLIED 29.92. SHE SAID SHE HAD US BELOW FL350 (FORGET THE EXACT ALT SHE SAID). WE CONFIRMED AGAIN WE WERE LEVEL AT FL350 WITH 29.92. WE THEN SWITCHED MODES ON THE MODE C RPTING, WENT TO STANDBY ON THE XPONDER, AND CHKED ALL SYS -- TO NO AVAIL. SHE NOW HAD US LEVEL AT FL310, YET WE WERE STILL AT FL350. SHE TRIED FOR QUITE SOME TIME TO GET ANOTHER ACFT (ACR Y, B737) TO SEE IF THEY COULD SEE US, BUT WE HAD NO OTHER ACFT ON OUR TCASII CLOSE TO US. IN ADDITION, WE HAD A NORMAL CLB TO FL350 AND WERE ON TOP OF A CLOUD SYS ABOUT 1000 FT BELOW US. AN ADDITIONAL CONFUSING PROB WAS THE FACT THAT THE CTLR KEPT CALLING US BY THE #XXXA INSTEAD OF #XXXB. WE TRIED SEVERAL TIMES TO CORRECT HER. AFTER QUITE A WHILE OF HER TALKING TO OTHERS, WE LOST HER VOICE COVERAGE AND CALLED IN THE BLIND FOR ANOTHER FREQ -- WHICH WE GOT, BUT WE WERE NEVER XFERRED. WE DON'T KNOW IF SHE MIXED UP ACFT WITH CALL SIGNS THAT WERE SIMILAR OR NOT. ON OUR DSCNT, WE GOT ACCURATE MODE C RPTS FROM EVERY CTLR AFTER HER -- NO INDICATION OF FAILURE OF DEGRADATION IN THE MODE C AT ALL, NOR ON THE SUCCEEDING FLT WHERE WE HAD REPEATED CHKS DONE ALL THE WAY UP TO FL330.
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.