Air carrier medium large transport altitude preselect fails to capture even though properly set.

Attributes
ACN	138183
Time
Date	199003
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sjc
State Reference	CA
Altitude	msl bound lower : 7500 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : private
Experience	flight time last 90 days : 130 flight time total : 3500 flight time type : 300
ASRS Report	138183
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

FGS was set at clamp, altitude armed at 8000' and annunciated so, heading select, IAS. The autoplt didn't capture at 8000' MSL. Was arrested at 7500' MSL manually and immediately returned to 8000', as cleared. This happens all too often with this FGS. Realizing that it is my responsibility to watch the autoplt during maneuvers such as these, I'm now going to push altitude hold when approaching assigned altitude. This is nonstandard procedure, but now seems necessary, since this is the third time in 3 days that the FGS has malfunctioned.

Original NASA ASRS Text

Title: ACR MLG ALT PRESELECT FAILS TO CAPTURE EVEN THOUGH PROPERLY SET.

Narrative: FGS WAS SET AT CLAMP, ALT ARMED AT 8000' AND ANNUNCIATED SO, HDG SELECT, IAS. THE AUTOPLT DIDN'T CAPTURE AT 8000' MSL. WAS ARRESTED AT 7500' MSL MANUALLY AND IMMEDIATELY RETURNED TO 8000', AS CLRED. THIS HAPPENS ALL TOO OFTEN WITH THIS FGS. REALIZING THAT IT IS MY RESPONSIBILITY TO WATCH THE AUTOPLT DURING MANEUVERS SUCH AS THESE, I'M NOW GOING TO PUSH ALT HOLD WHEN APCHING ASSIGNED ALT. THIS IS NONSTANDARD PROC, BUT NOW SEEMS NECESSARY, SINCE THIS IS THE THIRD TIME IN 3 DAYS THAT THE FGS HAS MALFUNCTIONED.

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.