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B737 flight crew descends below assigned altitude, even though both pilots believe otherwise. Flight crew believes cockpit procedures were correct. No ATC corrective action perceived.
| Attributes | |
| ACN | 397332 |
| Time | |
| Date | 199803 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : jhw |
| State Reference | NY |
| Altitude | msl bound lower : 28500 msl bound upper : 33000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zob |
| Operator | common carrier : air carrier |
| Make Model Name | B737-400 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | descent other |
| Route In Use | enroute other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 250 flight time total : 10000 flight time type : 5000 |
| ASRS Report | 397332 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 80 flight time total : 14500 flight time type : 10000 |
| ASRS Report | 397500 |
| Events | |
| Anomaly | altitude deviation : overshoot non adherence : clearance |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
We were at cruise at FL330. I was flying as first officer at controls, FMS navigating, autoplt was engaged. ATC gave us a clearance to descend to FL280. The captain read back the descent and pointed to the altitude alerter that I had dialed in to correspond to 28000 ft. I selected FL280 in the cruise page of the FMC, executed the command and the autoplt started our 1000 FPM rate of descent. At this phase of the flight, neither the captain nor myself had any cognitive reason to expect any specific altitude to descend to. As we descended through 28500 ft, the controller stated 'air carrier X, verify assigned altitude FL290.' the captain stated 'negative,' assigned FL280. Controller stated to maintain FL290. I immediately set up a 2000 FPM climb in vertical speed mode of autoplt back to FL290. There was no conflict noticed by either the captain or myself on TCASII, nor did the controller ever state a conflict had occurred. We then questioned the controller as to what was our original assigned altitude, and he stated that he had FL290 in 'his box' and that is what he would have to say was correct. Both the captain and I believe we were assigned FL280. Supplemental information from acn 397500: as the crew, we discussed the issue. We have no reason to believe there was a problem with our procedures or understanding of the clearance.
Original NASA ASRS Text
Title: B737 FLC DSNDS BELOW ASSIGNED ALT, EVEN THOUGH BOTH PLTS BELIEVE OTHERWISE. FLC BELIEVES COCKPIT PROCS WERE CORRECT. NO ATC CORRECTIVE ACTION PERCEIVED.
Narrative: WE WERE AT CRUISE AT FL330. I WAS FLYING AS FO AT CTLS, FMS NAVING, AUTOPLT WAS ENGAGED. ATC GAVE US A CLRNC TO DSND TO FL280. THE CAPT READ BACK THE DSCNT AND POINTED TO THE ALT ALERTER THAT I HAD DIALED IN TO CORRESPOND TO 28000 FT. I SELECTED FL280 IN THE CRUISE PAGE OF THE FMC, EXECUTED THE COMMAND AND THE AUTOPLT STARTED OUR 1000 FPM RATE OF DSCNT. AT THIS PHASE OF THE FLT, NEITHER THE CAPT NOR MYSELF HAD ANY COGNITIVE REASON TO EXPECT ANY SPECIFIC ALT TO DSND TO. AS WE DSNDED THROUGH 28500 FT, THE CTLR STATED 'ACR X, VERIFY ASSIGNED ALT FL290.' THE CAPT STATED 'NEGATIVE,' ASSIGNED FL280. CTLR STATED TO MAINTAIN FL290. I IMMEDIATELY SET UP A 2000 FPM CLB IN VERT SPD MODE OF AUTOPLT BACK TO FL290. THERE WAS NO CONFLICT NOTICED BY EITHER THE CAPT OR MYSELF ON TCASII, NOR DID THE CTLR EVER STATE A CONFLICT HAD OCCURRED. WE THEN QUESTIONED THE CTLR AS TO WHAT WAS OUR ORIGINAL ASSIGNED ALT, AND HE STATED THAT HE HAD FL290 IN 'HIS BOX' AND THAT IS WHAT HE WOULD HAVE TO SAY WAS CORRECT. BOTH THE CAPT AND I BELIEVE WE WERE ASSIGNED FL280. SUPPLEMENTAL INFO FROM ACN 397500: AS THE CREW, WE DISCUSSED THE ISSUE. WE HAVE NO REASON TO BELIEVE THERE WAS A PROB WITH OUR PROCS OR UNDERSTANDING OF THE CLRNC.
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.