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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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Falcon aircraft in cruise had erroneous altitude readout from transponder mode C. Controller had flight crew verify altitude and shortly an air carrier aircraft TCASII responded to the altitude readout and commanded evasive action. Problem corrected when changing altitudes.
| Attributes | |
| ACN | 368435 |
| Time | |
| Date | 199705 |
| Day | Mon |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : zab |
| State Reference | NM |
| Altitude | msl bound lower : 31000 msl bound upper : 32400 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zab |
| Operator | general aviation : corporate |
| Make Model Name | Falcon 10C |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | MD-80 Series (DC-9-80) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 14000 |
| ASRS Report | 368435 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument |
| Events | |
| Anomaly | aircraft equipment problem : less severe conflict : airborne less severe other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other controllera |
| Resolutory Action | aircraft : equipment problem dissipated flight crew : took evasive action other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
On may/xx/97, falcon, en route to palm springs, ca, was assigned FL310 by ZAB and was maintaining FL310 as verified by both aircraft altimeters and GPS altitude readouts. ZAB requested confirmation of our altitude and last assigned altitude. The assigned altitude and aircraft altitude was confirmed at FL310. ZAB then informed us it was indicating an altitude of FL324 and advised us of air carrier X position at 11 O'clock, FL330, at which time air carrier X reported traffic on their TCASII at that altitude and said they were taking evasive action. We then switched to #2 transponder and asked ZAB for an altitude readout at which time ZAB reported our altitude to be FL310. Moments later, we requested air carrier X position from ZAB and ZAB reported air carrier X to be at 9 O'clock position, 4 mi, but not in sight by us or them. Now someone on air carrier X flight stated this was unacceptable and wanted the aircraft's call sign to file some paperwork on this situation. Later, after we were assigned FL350, both xponders read the same and correct altitudes. In all other ATC sectors all the way to destination, including approach control at destination. I believe this situation was caused by some type electronic interference in that sector. How to prevent recurrence is unknown.
Original NASA ASRS Text
Title: FALCON ACFT IN CRUISE HAD ERRONEOUS ALT READOUT FROM XPONDER MODE C. CTLR HAD FLC VERIFY ALT AND SHORTLY AN ACR ACFT TCASII RESPONDED TO THE ALT READOUT AND COMMANDED EVASIVE ACTION. PROB CORRECTED WHEN CHANGING ALTS.
Narrative: ON MAY/XX/97, FALCON, ENRTE TO PALM SPRINGS, CA, WAS ASSIGNED FL310 BY ZAB AND WAS MAINTAINING FL310 AS VERIFIED BY BOTH ACFT ALTIMETERS AND GPS ALT READOUTS. ZAB REQUESTED CONFIRMATION OF OUR ALT AND LAST ASSIGNED ALT. THE ASSIGNED ALT AND ACFT ALT WAS CONFIRMED AT FL310. ZAB THEN INFORMED US IT WAS INDICATING AN ALT OF FL324 AND ADVISED US OF ACR X POS AT 11 O'CLOCK, FL330, AT WHICH TIME ACR X RPTED TFC ON THEIR TCASII AT THAT ALT AND SAID THEY WERE TAKING EVASIVE ACTION. WE THEN SWITCHED TO #2 XPONDER AND ASKED ZAB FOR AN ALT READOUT AT WHICH TIME ZAB RPTED OUR ALT TO BE FL310. MOMENTS LATER, WE REQUESTED ACR X POS FROM ZAB AND ZAB RPTED ACR X TO BE AT 9 O'CLOCK POS, 4 MI, BUT NOT IN SIGHT BY US OR THEM. NOW SOMEONE ON ACR X FLT STATED THIS WAS UNACCEPTABLE AND WANTED THE ACFT'S CALL SIGN TO FILE SOME PAPERWORK ON THIS SIT. LATER, AFTER WE WERE ASSIGNED FL350, BOTH XPONDERS READ THE SAME AND CORRECT ALTS. IN ALL OTHER ATC SECTORS ALL THE WAY TO DEST, INCLUDING APCH CTL AT DEST. I BELIEVE THIS SIT WAS CAUSED BY SOME TYPE ELECTRONIC INTERFERENCE IN THAT SECTOR. HOW TO PREVENT RECURRENCE IS UNKNOWN.
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.