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Requesting lower altitude. Both pilots in a B757 hear a garbled transmission from ZHU center ending with the number four and start down.
| Attributes | |
| ACN | 535787 |
| Time | |
| Date | 200201 |
| Day | Sat |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| State Reference | LA |
| Altitude | msl single value : 35000 |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zhu.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B757 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : zhu.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| ASRS Report | 535787 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 535788 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude inflight encounter : turbulence non adherence : far |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance none taken : anomaly accepted |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
We were level at FL350 with a rough ride. Captain flying. I requested a descent to FL310 for better ride. Several other aircraft on frequency with a '4' as he last number in their call sign and ATC controller was working at lest one other frequency. No response to initial request so I requested again. Radios somewhat garbled but we both thought we heard a descent clearance for us. I confirmed our clearance by saying aircraft X descending from FL350 to fl 310 and we got no response. We started down and at about FL335 ATC asked us to say altitude. We did responding that we were at FL335 descending to FL310. ATC requested we stop at FL330 and we did. A few seconds later ATC cleared us to FL310. ATC frequency was very congested by other traffic attempting to do the same thing, i.e., descending due to bad rides. I am not sure if we took someone else's clearance or if ATC didn't hear us. TCAS didn't go off and ATC wasn't obviously upset. Supplemental information from acn 537788: we both understood the clearance to descend to FL310 but center did not respond. They stated that we were not cleared to FL310. There was another same air carrier flight on the frequency with a similar sounding call sign.
Original NASA ASRS Text
Title: REQUESTING LOWER ALT. BOTH PLTS IN A B757 HEAR A GARBLED TRANSMISSION FROM ZHU CENTER ENDING WITH THE NUMBER FOUR AND START DOWN.
Narrative: WE WERE LEVEL AT FL350 WITH A ROUGH RIDE. CAPTAIN FLYING. I REQUESTED A DSCNT TO FL310 FOR BETTER RIDE. SEVERAL OTHER ACFT ON FREQ WITH A '4' AS HE LAST NUMBER IN THEIR CALL SIGN AND ATC CTLR WAS WORKING AT LEST ONE OTHER FREQ. NO RESPONSE TO INITIAL REQUEST SO I REQUESTED AGAIN. RADIOS SOMEWHAT GARBLED BUT WE BOTH THOUGHT WE HEARD A DSCNT CLRNC FOR US. I CONFIRMED OUR CLRNC BY SAYING ACFT X DESCENDING FROM FL350 TO FL 310 AND WE GOT NO RESPONSE. WE STARTED DOWN AND AT ABOUT FL335 ATC ASKED US TO SAY ALT. WE DID RESPONDING THAT WE WERE AT FL335 DESCENDING TO FL310. ATC REQUESTED WE STOP AT FL330 AND WE DID. A FEW SECS LATER ATC CLRED US TO FL310. ATC FREQ WAS VERY CONGESTED BY OTHER TFC ATTEMPTING TO DO THE SAME THING, I.E., DESCENDING DUE TO BAD RIDES. I AM NOT SURE IF WE TOOK SOMEONE ELSE'S CLRNC OR IF ATC DIDN'T HEAR US. TCAS DIDN'T GO OFF AND ATC WASN'T OBVIOUSLY UPSET. SUPPLEMENTAL INFO FROM ACN 537788: WE BOTH UNDERSTOOD THE CLRNC TO DESCEND TO FL310 BUT CENTER DID NOT RESPOND. THEY STATED THAT WE WERE NOT CLRED TO FL310. THERE WAS ANOTHER SAME ACR FLT ON THE FREQ WITH A SIMILAR SOUNDING CALL SIGN.
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.