An MD80 flight crew overshot altitude when the altitude capture feature of the autoplt malfunctioned...

Attributes
ACN	577181
Time
Date	200303
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : ptw.vortac
State Reference	PA
Altitude	msl bound lower : 28000 msl bound upper : 28800
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	577181
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude flight crew : became reoriented
Consequence	other
Supplementary
Problem Areas	ATC Human Performance Aircraft Flight Crew Human Performance Maintenance Human Performance Company
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During climb to FL280, autoplt #1 failed to capture altitude. Altitude capture was annunciated, autoplt mode changed to 'altitude' only, not 'altitude hold.' 2 prior logbook entries about this, but captured intermediate altitudes ok. I was distraction, preparing my cruise PA, and did not notice slow climb until FL288. Disconnected autoplt and descended promptly to FL280. Autoplt #2 used for remainder of flight. Autoplt #1 placarded at arrival station. No ATC deviations noted. I learned a good lesson -- not to assume altitude capture will always become altitude hold.

Original NASA ASRS Text

Title: AN MD80 FLT CREW OVERSHOT ALT WHEN THE ALT CAPTURE FEATURE OF THE AUTOPLT MALFUNCTIONED.

Narrative: DURING CLB TO FL280, AUTOPLT #1 FAILED TO CAPTURE ALT. ALT CAPTURE WAS ANNUNCIATED, AUTOPLT MODE CHANGED TO 'ALT' ONLY, NOT 'ALT HOLD.' 2 PRIOR LOGBOOK ENTRIES ABOUT THIS, BUT CAPTURED INTERMEDIATE ALTS OK. I WAS DISTR, PREPARING MY CRUISE PA, AND DID NOT NOTICE SLOW CLB UNTIL FL288. DISCONNECTED AUTOPLT AND DSNDED PROMPTLY TO FL280. AUTOPLT #2 USED FOR REMAINDER OF FLT. AUTOPLT #1 PLACARDED AT ARR STATION. NO ATC DEVS NOTED. I LEARNED A GOOD LESSON -- NOT TO ASSUME ALT CAPTURE WILL ALWAYS BECOME ALT HOLD.

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.