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Air carrier descended below assigned altitude due to miscom in the cockpit.
| Attributes | |
| ACN | 145137 |
| Time | |
| Date | 199005 |
| Day | Sun |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : aus |
| State Reference | TX |
| Altitude | msl bound lower : 17000 msl bound upper : 18000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other |
| Flight Phase | descent other |
| Route In Use | arrival other enroute airway : zhu |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 160 flight time total : 10000 flight time type : 1500 |
| ASRS Report | 145137 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : flight engineer |
| Experience | flight time last 90 days : 240 flight time total : 6000 flight time type : 1500 |
| ASRS Report | 144808 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : required legal separation non adherence : clearance other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance |
| Consequence | Other |
| Miss Distance | horizontal : 18000 vertical : 500 |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
On arwy between act and aus at FL180. Given pilot's discretion to 11000'. A few mins later (still at FL180) we were told to turn right to a heading (about 250 degrees) and maintain FL180. About 2 more mins on that heading and we were then cleared direct aus, marcs 1 sat. Shortly after this I advised the first officer I was leaving the center frequency to get the ATIS. While copying the ATIS I observed the first officer begin a descent, talk to ATC, and (I thought) reset the altitude alerter to 11000'. I returned to center frequency a few moments later just in time to hear ATC ask if we were descending. We were now at 17100'. ATC told us we had traffic at 12 O'clock and 3 mi at 17500'. They then cleared us to 12000'. It seems the first officer never heard the clearance to maintain FL180 when we were turned to the 250 degree heading. Still thinking our discretion to 11000', he left FL180 and reported leaving to ATC. They did not acknowledged. He thinks 11000' was set in the alerter. When I saw him talking to ATC, I assumed he was being cleared to a lower altitude! Supplemental information from acn 144808: we were level at FL180, then given pilot's discretion to 11000'. We maintained FL180 and ATC gave us a vector. ATC then cleared us direct aus VOR for marcs 1 arrival and to maintain FL180. I heard clear to aus, but not to maintain FL180. The captain went off frequency to get ATIS. I was still thinking we were cleared to 11000'. I reported leaving FL170 for 11000', but didn't get a reply.
Original NASA ASRS Text
Title: ACR DESCENDED BELOW ASSIGNED ALT DUE TO MISCOM IN THE COCKPIT.
Narrative: ON ARWY BTWN ACT AND AUS AT FL180. GIVEN PLT'S DISCRETION TO 11000'. A FEW MINS LATER (STILL AT FL180) WE WERE TOLD TO TURN RIGHT TO A HDG (ABOUT 250 DEGS) AND MAINTAIN FL180. ABOUT 2 MORE MINS ON THAT HDG AND WE WERE THEN CLRED DIRECT AUS, MARCS 1 SAT. SHORTLY AFTER THIS I ADVISED THE F/O I WAS LEAVING THE CENTER FREQ TO GET THE ATIS. WHILE COPYING THE ATIS I OBSERVED THE F/O BEGIN A DSNT, TALK TO ATC, AND (I THOUGHT) RESET THE ALT ALERTER TO 11000'. I RETURNED TO CENTER FREQ A FEW MOMENTS LATER JUST IN TIME TO HEAR ATC ASK IF WE WERE DSNDING. WE WERE NOW AT 17100'. ATC TOLD US WE HAD TFC AT 12 O'CLOCK AND 3 MI AT 17500'. THEY THEN CLRED US TO 12000'. IT SEEMS THE F/O NEVER HEARD THE CLRNC TO MAINTAIN FL180 WHEN WE WERE TURNED TO THE 250 DEG HDG. STILL THINKING OUR DISCRETION TO 11000', HE LEFT FL180 AND RPTED LEAVING TO ATC. THEY DID NOT ACKNOWLEDGED. HE THINKS 11000' WAS SET IN THE ALERTER. WHEN I SAW HIM TALKING TO ATC, I ASSUMED HE WAS BEING CLRED TO A LOWER ALT! SUPPLEMENTAL INFO FROM ACN 144808: WE WERE LEVEL AT FL180, THEN GIVEN PLT'S DISCRETION TO 11000'. WE MAINTAINED FL180 AND ATC GAVE US A VECTOR. ATC THEN CLRED US DIRECT AUS VOR FOR MARCS 1 ARR AND TO MAINTAIN FL180. I HEARD CLR TO AUS, BUT NOT TO MAINTAIN FL180. THE CAPT WENT OFF FREQ TO GET ATIS. I WAS STILL THINKING WE WERE CLRED TO 11000'. I RPTED LEAVING FL170 FOR 11000', BUT DIDN'T GET A REPLY.
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.