Flight crew of MD88 on descent with FMS properly programmed has altitude deviation when autoplt fails to capture altitude. They immediately climb back to assigned altitude.

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Attributes
ACN	396730
Time
Date	199803
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : lhy
State Reference	PA
Altitude	msl bound lower : 10700 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zny
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 250 flight time total : 6500 flight time type : 300
ASRS Report	396730
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	396733
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

In a descent to 11000 ft MSL autoplt on, vertical navigation/FMS in operation, VNAV capture displayed on the FMA approaching 11000 ft. Altitude hold displayed on the FMA at 11000 ft however aircraft continued descent. I engaged vertical speed to bring aircraft back up at approximately 10850 ft. Aircraft went as low as 10700 ft before climbing back up to 11000 ft MSL.

Original NASA ASRS Text

Title: FLC OF MD88 ON DSCNT WITH FMS PROPERLY PROGRAMMED HAS ALTDEV WHEN AUTOPLT FAILS TO CAPTURE ALT. THEY IMMEDIATELY CLB BACK TO ASSIGNED ALT.

Narrative: IN A DSCNT TO 11000 FT MSL AUTOPLT ON, VERT NAV/FMS IN OP, VNAV CAPTURE DISPLAYED ON THE FMA APCHING 11000 FT. ALT HOLD DISPLAYED ON THE FMA AT 11000 FT HOWEVER ACFT CONTINUED DSCNT. I ENGAGED VERT SPD TO BRING ACFT BACK UP AT APPROX 10850 FT. ACFT WENT AS LOW AS 10700 FT BEFORE CLBING BACK UP TO 11000 FT MSL.

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.