Flight crew of a B757 undershot descent altitude resulting in not meeting a crossing restr. The flight crew's inattn to the aircraft autoplt action, of which they thought was preprogrammed to descend the aircraft in time to meet the crossing restr, caused the aircraft to be 2000 ft high at crossing fix.

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Attributes
ACN	365344
Time
Date	199704
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : fnt
State Reference	MI
Altitude	msl bound lower : 31000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 170 flight time total : 20000 flight time type : 2000
ASRS Report	365344
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	other other : other pilot : atp
Experience	flight time last 90 days : 100 flight time total : 9000 flight time type : 150
ASRS Report	365347
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : crossing restriction not met altitude deviation : undershoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While 70 NM east of dewitt, we were given a clearance to cross dewitt at FL310. The MCA altitude was set to FL310 and the restr entered into the FMC. 5 NM from the programmed top of descent, 'descend now' was activated. The throttles came back and the descent began. After beginning the descent, I briefed the upcoming approach. I expected the aircraft to automatically fly the restr like it is supposed to do. The center asked if we had a crossing restr. We looked up from our briefing and saw that we had crossed dewitt and were still descending through FL330 at about 1000 FPM. We checked and we were still in VNAV but the throttles were not at idle. We quickly idled the throttles and expedited descent. Center had traffic at FL330. Confused at why the aircraft did not make its restr, we set up a similar situation but this time the aircraft met the restr. We don't know why the aircraft didn't meet the first restr but we can only guess we did something wrong. Perhaps the early pickup (XA15 home time) contributed. I normally go to sleep around XB00 at home and didn't even come close to a full night's sleep prior to the incident.

Original NASA ASRS Text

Title: FLC OF A B757 UNDERSHOT DSCNT ALT RESULTING IN NOT MEETING A XING RESTR. THE FLC'S INATTN TO THE ACFT AUTOPLT ACTION, OF WHICH THEY THOUGHT WAS PREPROGRAMMED TO DSND THE ACFT IN TIME TO MEET THE XING RESTR, CAUSED THE ACFT TO BE 2000 FT HIGH AT XING FIX.

Narrative: WHILE 70 NM E OF DEWITT, WE WERE GIVEN A CLRNC TO CROSS DEWITT AT FL310. THE MCA ALT WAS SET TO FL310 AND THE RESTR ENTERED INTO THE FMC. 5 NM FROM THE PROGRAMMED TOP OF DSCNT, 'DSND NOW' WAS ACTIVATED. THE THROTTLES CAME BACK AND THE DSCNT BEGAN. AFTER BEGINNING THE DSCNT, I BRIEFED THE UPCOMING APCH. I EXPECTED THE ACFT TO AUTOMATICALLY FLY THE RESTR LIKE IT IS SUPPOSED TO DO. THE CTR ASKED IF WE HAD A XING RESTR. WE LOOKED UP FROM OUR BRIEFING AND SAW THAT WE HAD CROSSED DEWITT AND WERE STILL DSNDING THROUGH FL330 AT ABOUT 1000 FPM. WE CHKED AND WE WERE STILL IN VNAV BUT THE THROTTLES WERE NOT AT IDLE. WE QUICKLY IDLED THE THROTTLES AND EXPEDITED DSCNT. CTR HAD TFC AT FL330. CONFUSED AT WHY THE ACFT DID NOT MAKE ITS RESTR, WE SET UP A SIMILAR SIT BUT THIS TIME THE ACFT MET THE RESTR. WE DON'T KNOW WHY THE ACFT DIDN'T MEET THE FIRST RESTR BUT WE CAN ONLY GUESS WE DID SOMETHING WRONG. PERHAPS THE EARLY PICKUP (XA15 HOME TIME) CONTRIBUTED. I NORMALLY GO TO SLEEP AROUND XB00 AT HOME AND DIDN'T EVEN COME CLOSE TO A FULL NIGHT'S SLEEP PRIOR TO THE INCIDENT.

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.