B737 crew depends on FMS for computations and miss crossing restr.

Attributes
ACN	453490
Time
Date	199910
Day	Mon
Local Time Of Day	1801 To 2400
Place
State Reference	VA
Altitude	msl bound lower : 14000 msl bound upper : 15100
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zdc.artcc tower : cak.tower
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : atp pilot : cfi
Experience	flight time last 90 days : 135 flight time total : 8000 flight time type : 3800
ASRS Report	453490
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : multi engine
Events
Anomaly	altitude deviation : crossing restriction not met non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	none taken : insufficient time
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight from isp-bwi. Speed and altitude controled from takeoff because of flow in washington airspace. During descent, airspeed was controled from 250 KTS to 280 KTS. This was changed back and forth a couple of times. Descent altitudes were given in 1000 and 2000 ft blocks until the center told me to be at zizzi at 14000 ft. I was already in a 1000-1200 FPM descent when given this clearance. I entered the altitude into the FMC so the computer could help figure the descent required. Although the FMS took the change, the descent page showed the descent based on the altitude over the OM which was still 40 NM away. It showed a descent rate of 1100 FPM, which is what I was doing. (My partner was getting ATIS from bwi during this period.) approximately 7 NM from zizzi, I noticed the discrepancy. We were very high, assigned 280 KTS for spacing. I deployed the spoilers and went to idle. Passed over zizzi 1000-1100 ft high. Reached 14000 ft, 3 - 3 1/2 NM past zizzi. No traffic conflict was noted. The controller did not say anything. The FMC is a great tool, but do not depend on it to keep you legal.

Original NASA ASRS Text

Title: B737 CREW DEPENDS ON FMS FOR COMPUTATIONS AND MISS XING RESTR.

Narrative: FLT FROM ISP-BWI. SPD AND ALT CTLED FROM TKOF BECAUSE OF FLOW IN WASHINGTON AIRSPACE. DURING DSCNT, AIRSPD WAS CTLED FROM 250 KTS TO 280 KTS. THIS WAS CHANGED BACK AND FORTH A COUPLE OF TIMES. DSCNT ALTS WERE GIVEN IN 1000 AND 2000 FT BLOCKS UNTIL THE CTR TOLD ME TO BE AT ZIZZI AT 14000 FT. I WAS ALREADY IN A 1000-1200 FPM DSCNT WHEN GIVEN THIS CLRNC. I ENTERED THE ALT INTO THE FMC SO THE COMPUTER COULD HELP FIGURE THE DSCNT REQUIRED. ALTHOUGH THE FMS TOOK THE CHANGE, THE DSCNT PAGE SHOWED THE DSCNT BASED ON THE ALT OVER THE OM WHICH WAS STILL 40 NM AWAY. IT SHOWED A DSCNT RATE OF 1100 FPM, WHICH IS WHAT I WAS DOING. (MY PARTNER WAS GETTING ATIS FROM BWI DURING THIS PERIOD.) APPROX 7 NM FROM ZIZZI, I NOTICED THE DISCREPANCY. WE WERE VERY HIGH, ASSIGNED 280 KTS FOR SPACING. I DEPLOYED THE SPOILERS AND WENT TO IDLE. PASSED OVER ZIZZI 1000-1100 FT HIGH. REACHED 14000 FT, 3 - 3 1/2 NM PAST ZIZZI. NO TFC CONFLICT WAS NOTED. THE CTLR DID NOT SAY ANYTHING. THE FMC IS A GREAT TOOL, BUT DO NOT DEPEND ON IT TO KEEP YOU LEGAL.

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.