Aircraft placarded one autoplt inoperative. Flight crew accepted aircraft. In flight, autoplt clicke...

Attributes
ACN	126686
Time
Date	198910
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 33000 msl bound upper : 33400
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 170 flight time total : 7000 flight time type : 170
ASRS Report	126686
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

The aircraft that we were dispatched with out of lax to dtw had the #1 autoplt placarded as inoperative. The MEL permits the use of just 1 autoplt for dispatch, so we took the aircraft. Shortly after level off at FL330 the autoplt clicked 'off', effectively turning off the navigation and pitch/roll functions of the autoflt system. For some reason, the autoplt did not have the aircraft in a trimmed condition, so it immediately initiated a climb. I rather abruptly grabbed the yoke, applied forward pressure, and 'leveled off' at about 33,300' then I slowly eased the aircraft back down to FL330 and smoothly reengaged all the autoplt systems. Approximately 10 mins later the autoplt tripped off again. Once again we were in smooth air, and unfortunately the autoplt was not trimmed straight and level so the aircraft immediately started to climb, again. The results were about the same again for the recovery. We climbed about 250-300' and then slid on back down to our assigned altitude. This happened a total of 13 times en route to detroit. We mentioned it to ATC. Each time the altitude deviation exceeded 300' and once it was 400'. ATC always said something like 'ok don't worry about it.'

Original NASA ASRS Text

Title: ACFT PLACARDED ONE AUTOPLT INOPERATIVE. FLT CREW ACCEPTED ACFT. IN FLT, AUTOPLT CLICKED OFF 13 TIMES, WITH AN ALT EXCURSION EACH TIME.

Narrative: THE ACFT THAT WE WERE DISPATCHED WITH OUT OF LAX TO DTW HAD THE #1 AUTOPLT PLACARDED AS INOP. THE MEL PERMITS THE USE OF JUST 1 AUTOPLT FOR DISPATCH, SO WE TOOK THE ACFT. SHORTLY AFTER LEVEL OFF AT FL330 THE AUTOPLT CLICKED 'OFF', EFFECTIVELY TURNING OFF THE NAVIGATION AND PITCH/ROLL FUNCTIONS OF THE AUTOFLT SYSTEM. FOR SOME REASON, THE AUTOPLT DID NOT HAVE THE ACFT IN A TRIMMED CONDITION, SO IT IMMEDIATELY INITIATED A CLIMB. I RATHER ABRUPTLY GRABBED THE YOKE, APPLIED FORWARD PRESSURE, AND 'LEVELED OFF' AT ABOUT 33,300' THEN I SLOWLY EASED THE ACFT BACK DOWN TO FL330 AND SMOOTHLY REENGAGED ALL THE AUTOPLT SYSTEMS. APPROX 10 MINS LATER THE AUTOPLT TRIPPED OFF AGAIN. ONCE AGAIN WE WERE IN SMOOTH AIR, AND UNFORTUNATELY THE AUTOPLT WAS NOT TRIMMED STRAIGHT AND LEVEL SO THE ACFT IMMEDIATELY STARTED TO CLIMB, AGAIN. THE RESULTS WERE ABOUT THE SAME AGAIN FOR THE RECOVERY. WE CLIMBED ABOUT 250-300' AND THEN SLID ON BACK DOWN TO OUR ASSIGNED ALT. THIS HAPPENED A TOTAL OF 13 TIMES ENRTE TO DETROIT. WE MENTIONED IT TO ATC. EACH TIME THE ALT DEVIATION EXCEEDED 300' AND ONCE IT WAS 400'. ATC ALWAYS SAID SOMETHING LIKE 'OK DON'T WORRY ABOUT IT.'

Data retrieved from NASA's ASRS site as of August 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.

Aircraft placarded one autoplt inoperative. Flight crew accepted aircraft. In flight, autoplt clicked off 13 times, with an altitude excursion each time.