Narrative:

Flight cruise level of FL270, stepped down to FL250, then FL220. Received clearance to cross falko intersection at 10000 ft, at 250 KIAS. Programmed the FMS to cruise at FL220, and to cross falko intersection at 10000 ft, at 250 KIAS. I normally keep the FMS on the 'progress' page to display distance to computer top of descent. I thought the FMS showed 70 mi to top of descent, when in fact it was displaying 70 mi to end of descent, indicating that we were already past the computed top of descent. On my next scan of the FMS I noticed the readout was 65 mi to end of descent, and I immediately realized that our descent was very late. I retarded the throttles to idle, extended the speed brakes and began a rapid descent. At this time ATC called and asked us to begin our descent, to which we replied that we were hurrying down now. As we approached falko, it was very obvious that we were not going to make the crossing restr, so the first officer informed ATC and asked if we could be vectored for the descent or if it would be okay if we were high and fast. ATC told us to standby. As we passed falko at approximately 12500 ft at 300 KIAS, ATC said that the high and fast would be ok. Flight proceeded to iad without further incident. This incident seems to have been a result of the failure of the FMS to initiate the descent at the computed top of descent point. However, I failed to detect the problem soon enough to avert the deviation. My only excuse, and it is obviously a very weak one, can be summed up in 1 word -- complacency. After literally hundreds of FMS initiated dscnts at the precise point, one tends to make a potentially fatal mistake -- reliance on the machine. I have had this lesson brought home before, but with the modern glass cockpit and computer aided flight it is so terribly easy to expect the machine to be correct (as it is 999 times out of 1000) that the ultimate computer -- the human brain -- ceases to function.

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Original NASA ASRS Text

Title: ALT XING RESTR. ACR MISPROGRAMS FMC AND ENDS UP HIGH AND FAST AT THE XING POINT.

Narrative: FLT CRUISE LEVEL OF FL270, STEPPED DOWN TO FL250, THEN FL220. RECEIVED CLRNC TO CROSS FALKO INTXN AT 10000 FT, AT 250 KIAS. PROGRAMMED THE FMS TO CRUISE AT FL220, AND TO CROSS FALKO INTXN AT 10000 FT, AT 250 KIAS. I NORMALLY KEEP THE FMS ON THE 'PROGRESS' PAGE TO DISPLAY DISTANCE TO COMPUTER TOP OF DSCNT. I THOUGHT THE FMS SHOWED 70 MI TO TOP OF DSCNT, WHEN IN FACT IT WAS DISPLAYING 70 MI TO END OF DSCNT, INDICATING THAT WE WERE ALREADY PAST THE COMPUTED TOP OF DSCNT. ON MY NEXT SCAN OF THE FMS I NOTICED THE READOUT WAS 65 MI TO END OF DSCNT, AND I IMMEDIATELY REALIZED THAT OUR DSCNT WAS VERY LATE. I RETARDED THE THROTTLES TO IDLE, EXTENDED THE SPD BRAKES AND BEGAN A RAPID DSCNT. AT THIS TIME ATC CALLED AND ASKED US TO BEGIN OUR DSCNT, TO WHICH WE REPLIED THAT WE WERE HURRYING DOWN NOW. AS WE APCHED FALKO, IT WAS VERY OBVIOUS THAT WE WERE NOT GOING TO MAKE THE XING RESTR, SO THE FO INFORMED ATC AND ASKED IF WE COULD BE VECTORED FOR THE DSCNT OR IF IT WOULD BE OKAY IF WE WERE HIGH AND FAST. ATC TOLD US TO STANDBY. AS WE PASSED FALKO AT APPROX 12500 FT AT 300 KIAS, ATC SAID THAT THE HIGH AND FAST WOULD BE OK. FLT PROCEEDED TO IAD WITHOUT FURTHER INCIDENT. THIS INCIDENT SEEMS TO HAVE BEEN A RESULT OF THE FAILURE OF THE FMS TO INITIATE THE DSCNT AT THE COMPUTED TOP OF DSCNT POINT. HOWEVER, I FAILED TO DETECT THE PROB SOON ENOUGH TO AVERT THE DEV. MY ONLY EXCUSE, AND IT IS OBVIOUSLY A VERY WEAK ONE, CAN BE SUMMED UP IN 1 WORD -- COMPLACENCY. AFTER LITERALLY HUNDREDS OF FMS INITIATED DSCNTS AT THE PRECISE POINT, ONE TENDS TO MAKE A POTENTIALLY FATAL MISTAKE -- RELIANCE ON THE MACHINE. I HAVE HAD THIS LESSON BROUGHT HOME BEFORE, BUT WITH THE MODERN GLASS COCKPIT AND COMPUTER AIDED FLT IT IS SO TERRIBLY EASY TO EXPECT THE MACHINE TO BE CORRECT (AS IT IS 999 TIMES OUT OF 1000) THAT THE ULTIMATE COMPUTER -- THE HUMAN BRAIN -- CEASES TO FUNCTION.

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.