Narrative:

At cruise altitude and at intermediate assigned altitude of FL350, ATC cleared us to FL270 to cross FL290 in 2 mins or less. Captain initiated descent selecting 1700 FPM vertical speed on autoplt mode control panel where upon he selected 3000 FPM rate to comply with the descent restriction. He then began to program, or attempt to program, the FMS for the descent. After descending approximately 3000' (at FL320), he apparently changed descent mode from vertical speed to another mode, what I believe was VNAV on the FMS. The aircraft slowed the rate of descent and almost leveled off just below FL320. As I started to make a reference to our restriction and the fact that we were not descending, ATC called and asked if we were going to make the restriction. The captain replied that he could. I replied to the controller that we still had some time left, but would appreciate a vector to be sure. The captain selected vertical speed again, then flight level change deploying the spoilers, and we descended through FL240 after turning approximately 30 degrees toward the controller's assigned heading. For both the captain and and I, this was our second trip on the widebody transport. The captain's attempt to use all the electronic aids available to comply with an intermediate descent that should have been little more than routine. Though a descent clearance from high altitude requiring a 3000 FPM rate of descent or more is a little unusual, it was not beyond the capability of the aircraft, even if not the most comfortable for the passenger. Though the FMS and associated capabilities greatly reduce workload when parameters can be preprogrammed or easily entered and executed, sometimes it is not the most expeditious way to carry out a task. The descent restriction could have been made with the initial selection of V/south. Incorporating the FMS almost caused us to miss it altogether.

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Original NASA ASRS Text

Title: MISSED CROSSING RESTRICTION ACCOUNT FMS REVERTED TO VNAV AND WAS NOT NOTICED BY THE FLT CREW.

Narrative: AT CRUISE ALT AND AT INTERMEDIATE ASSIGNED ALT OF FL350, ATC CLRED US TO FL270 TO CROSS FL290 IN 2 MINS OR LESS. CAPT INITIATED DSCNT SELECTING 1700 FPM VERT SPD ON AUTOPLT MODE CTL PANEL WHERE UPON HE SELECTED 3000 FPM RATE TO COMPLY WITH THE DSCNT RESTRICTION. HE THEN BEGAN TO PROGRAM, OR ATTEMPT TO PROGRAM, THE FMS FOR THE DSCNT. AFTER DSNDING APPROX 3000' (AT FL320), HE APPARENTLY CHANGED DSCNT MODE FROM VERT SPD TO ANOTHER MODE, WHAT I BELIEVE WAS VNAV ON THE FMS. THE ACFT SLOWED THE RATE OF DSCNT AND ALMOST LEVELED OFF JUST BELOW FL320. AS I STARTED TO MAKE A REF TO OUR RESTRICTION AND THE FACT THAT WE WERE NOT DSNDING, ATC CALLED AND ASKED IF WE WERE GOING TO MAKE THE RESTRICTION. THE CAPT REPLIED THAT HE COULD. I REPLIED TO THE CTLR THAT WE STILL HAD SOME TIME LEFT, BUT WOULD APPRECIATE A VECTOR TO BE SURE. THE CAPT SELECTED VERT SPD AGAIN, THEN FLT LEVEL CHANGE DEPLOYING THE SPOILERS, AND WE DSNDED THROUGH FL240 AFTER TURNING APPROX 30 DEGS TOWARD THE CTLR'S ASSIGNED HDG. FOR BOTH THE CAPT AND AND I, THIS WAS OUR SECOND TRIP ON THE WDB. THE CAPT'S ATTEMPT TO USE ALL THE ELECTRONIC AIDS AVAILABLE TO COMPLY WITH AN INTERMEDIATE DSCNT THAT SHOULD HAVE BEEN LITTLE MORE THAN ROUTINE. THOUGH A DSCNT CLRNC FROM HIGH ALT REQUIRING A 3000 FPM RATE OF DSCNT OR MORE IS A LITTLE UNUSUAL, IT WAS NOT BEYOND THE CAPABILITY OF THE ACFT, EVEN IF NOT THE MOST COMFORTABLE FOR THE PAX. THOUGH THE FMS AND ASSOCIATED CAPABILITIES GREATLY REDUCE WORKLOAD WHEN PARAMETERS CAN BE PREPROGRAMMED OR EASILY ENTERED AND EXECUTED, SOMETIMES IT IS NOT THE MOST EXPEDITIOUS WAY TO CARRY OUT A TASK. THE DSCNT RESTRICTION COULD HAVE BEEN MADE WITH THE INITIAL SELECTION OF V/S. INCORPORATING THE FMS ALMOST CAUSED US TO MISS IT ALTOGETHER.

Data retrieved from NASA's ASRS site as of August 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.