Autoplt malfunction overshot assigned altitude.

Attributes
ACN	168642
Time
Date	199101
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 37000 msl bound upper : 37300
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau tower : anc
Operator	general aviation : instructional
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 8000 flight time type : 200
ASRS Report	168642
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

The aircraft was in the flight director autoplt navigation mode using the INS for navigation when just prior to reaching FL370 the aircraft stated banking left and right at which time I noticed a red navigation flag in indicator #1. In order to get the aircraft back under control, I engaged the heading mode and moved the heading bug to my present heading. Just at that time, the altitude warning chime went off indicating the aircraft was at FL373. I immediately pitched down using the trim button because the aircraft was not responding fast enough. I disengaged the autoplt and with greater force I pitched the aircraft down even further in order to get back to FL370. After reaching FL370 I engaged the altitude hold button, but it did not come on. I repeatedly tried to engage it with no success. I then asked my copilot to try and after holding steady firm pressure while wiggling the button, it finally came on. After a few mins, I disengaged it and tried to engage it again with exactly the same result. Only after continued firm pressure while wiggling the button would it engage. During this sequence of events, I was still unable to correct the problem with the flight director navigation mode and had to use the heading mode. During this time the only call from ATC concerning altitude was to verify at FL370, and that was after a frequency change. I continued on to my destination, washington dc, with no further problems.

Original NASA ASRS Text

Title: AUTOPLT MALFUNCTION OVERSHOT ASSIGNED ALT.

Narrative: THE ACFT WAS IN THE FLT DIRECTOR AUTOPLT NAV MODE USING THE INS FOR NAV WHEN JUST PRIOR TO REACHING FL370 THE ACFT STATED BANKING L AND R AT WHICH TIME I NOTICED A RED NAV FLAG IN INDICATOR #1. IN ORDER TO GET THE ACFT BACK UNDER CTL, I ENGAGED THE HDG MODE AND MOVED THE HDG BUG TO MY PRESENT HDG. JUST AT THAT TIME, THE ALT WARNING CHIME WENT OFF INDICATING THE ACFT WAS AT FL373. I IMMEDIATELY PITCHED DOWN USING THE TRIM BUTTON BECAUSE THE ACFT WAS NOT RESPONDING FAST ENOUGH. I DISENGAGED THE AUTOPLT AND WITH GREATER FORCE I PITCHED THE ACFT DOWN EVEN FURTHER IN ORDER TO GET BACK TO FL370. AFTER REACHING FL370 I ENGAGED THE ALT HOLD BUTTON, BUT IT DID NOT COME ON. I REPEATEDLY TRIED TO ENGAGE IT WITH NO SUCCESS. I THEN ASKED MY COPLT TO TRY AND AFTER HOLDING STEADY FIRM PRESSURE WHILE WIGGLING THE BUTTON, IT FINALLY CAME ON. AFTER A FEW MINS, I DISENGAGED IT AND TRIED TO ENGAGE IT AGAIN WITH EXACTLY THE SAME RESULT. ONLY AFTER CONTINUED FIRM PRESSURE WHILE WIGGLING THE BUTTON WOULD IT ENGAGE. DURING THIS SEQUENCE OF EVENTS, I WAS STILL UNABLE TO CORRECT THE PROB WITH THE FLT DIRECTOR NAV MODE AND HAD TO USE THE HDG MODE. DURING THIS TIME THE ONLY CALL FROM ATC CONCERNING ALT WAS TO VERIFY AT FL370, AND THAT WAS AFTER A FREQ CHANGE. I CONTINUED ON TO MY DEST, WASHINGTON DC, WITH NO FURTHER PROBS.

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.