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Misunderstood clearance leaves B737 flight crew at wrong altitude in spite of readback until possible traffic conflict is caught by controller.
| Attributes | |
| ACN | 453210 |
| Time | |
| Date | 199910 |
| Day | Fri |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| State Reference | CA |
| Altitude | msl bound lower : 28000 msl bound upper : 29000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zla.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | climbout : intermediate altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp pilot : multi engine pilot : flight engineer |
| Experience | flight time last 90 days : 210 flight time total : 16000 flight time type : 4000 |
| ASRS Report | 453210 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument pilot : multi engine |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other controllerb |
| Resolutory Action | controller : issued new clearance controller : issued advisory flight crew : returned to assigned altitude |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance ATC Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Intra Facility Coordination Failure Pilot Deviation |
Narrative:
We understood from ZLA, going by gorman VOR, that we were cleared to FL290. We were given a frequency change as we leveled at FL290. We checked in and flew at FL290 for several mins. ZLA then came on and said that we were assigned FL280 and that we needed to return to FL280 within 40 seconds. First, however, center said to turn left 40 degrees for our climb. We turned left and descended to FL280. Nothing more was said. I asked for the center phone number to call upon our arrival. I was working the radio at the time, my first officer set in the assigned altitude. We were not advised of any loss of separation with any other aircraft.
Original NASA ASRS Text
Title: MISUNDERSTOOD CLRNC LEAVES B737 FLC AT WRONG ALT IN SPITE OF READBACK UNTIL POSSIBLE TFC CONFLICT IS CAUGHT BY CTLR.
Narrative: WE UNDERSTOOD FROM ZLA, GOING BY GORMAN VOR, THAT WE WERE CLRED TO FL290. WE WERE GIVEN A FREQ CHANGE AS WE LEVELED AT FL290. WE CHKED IN AND FLEW AT FL290 FOR SEVERAL MINS. ZLA THEN CAME ON AND SAID THAT WE WERE ASSIGNED FL280 AND THAT WE NEEDED TO RETURN TO FL280 WITHIN 40 SECONDS. FIRST, HOWEVER, CTR SAID TO TURN L 40 DEGS FOR OUR CLB. WE TURNED L AND DSNDED TO FL280. NOTHING MORE WAS SAID. I ASKED FOR THE CTR PHONE NUMBER TO CALL UPON OUR ARR. I WAS WORKING THE RADIO AT THE TIME, MY FO SET IN THE ASSIGNED ALT. WE WERE NOT ADVISED OF ANY LOSS OF SEPARATION WITH ANY OTHER ACFT.
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.