Pilot deviation autoplt descent below assigned altitude.

Attributes
ACN	293066
Time
Date	199501
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dca
State Reference	DC
Altitude	msl bound lower : 4800 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dca
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 121
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 500
ASRS Report	293066
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cleared to 5000 ft. PF was using autoplt and had engaged altitude hold at 5000 ft. It had locked on and leveled. Approximately 30 seconds later, PNF noted the altitude at 4800 and descending. PF disconnected the autoplt, recovered to 5000 ft. Maximum altitude loss was approximately 275 ft. Supplemental information from acn 293060: autoplt subsequently did not malfunction again.

Original NASA ASRS Text

Title: PLTDEV AUTOPLT DSCNT BELOW ASSIGNED ALT.

Narrative: CLRED TO 5000 FT. PF WAS USING AUTOPLT AND HAD ENGAGED ALT HOLD AT 5000 FT. IT HAD LOCKED ON AND LEVELED. APPROX 30 SECONDS LATER, PNF NOTED THE ALT AT 4800 AND DSNDING. PF DISCONNECTED THE AUTOPLT, RECOVERED TO 5000 FT. MAX ALT LOSS WAS APPROX 275 FT. SUPPLEMENTAL INFO FROM ACN 293060: AUTOPLT SUBSEQUENTLY DID NOT MALFUNCTION AGAIN.

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.