Flight crew of a widebody transport drifted off altitude due to an autoplt disconnect problem.

Attributes
ACN	316700
Time
Date	199509
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 35000 msl bound upper : 35700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	DC-10 10
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	other other : other pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 215 flight time total : 11600 flight time type : 2750
ASRS Report	316700
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 other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

We were in cruise flight at FL350 in a DC10-10, autoplt 2 disengaged. Flashing red disconnect lights did not illuminate. We climbed to FL357. Amber warning light did not illuminate indicating this deviation. Aural warning did not sound. All altitude alerter warnings were inoperative. Altitude hold on FMA was still illuminated. Our first indication was a transmission from ATC asking us if we were aware that we were at 35700 ft. None of the 3 crew members were aware of our deviation. We returned to FL350. I asked if there had been a conflict. ATC answered 'no conflict.' I asked if there was going to be a problem. ATC answered, 'absolutely not, no problem.' autoplt #2 was the culprit. We reengaged autoplt #2 at XA55 PDT. Approximately 1 min later with altitude hold illuminated, the aircraft started to climb. No aural or light warnings occurred. Returned to autoplt #1 for remainder of flight. This was a repeat write-up which was signed off the day before as 'operations (check) ok.'

Original NASA ASRS Text

Title: FLC OF A WDB DRIFTED OFF ALT DUE TO AN AUTOPLT DISCONNECT PROB.

Narrative: WE WERE IN CRUISE FLT AT FL350 IN A DC10-10, AUTOPLT 2 DISENGAGED. FLASHING RED DISCONNECT LIGHTS DID NOT ILLUMINATE. WE CLBED TO FL357. AMBER WARNING LIGHT DID NOT ILLUMINATE INDICATING THIS DEV. AURAL WARNING DID NOT SOUND. ALL ALT ALERTER WARNINGS WERE INOP. ALT HOLD ON FMA WAS STILL ILLUMINATED. OUR FIRST INDICATION WAS A XMISSION FROM ATC ASKING US IF WE WERE AWARE THAT WE WERE AT 35700 FT. NONE OF THE 3 CREW MEMBERS WERE AWARE OF OUR DEV. WE RETURNED TO FL350. I ASKED IF THERE HAD BEEN A CONFLICT. ATC ANSWERED 'NO CONFLICT.' I ASKED IF THERE WAS GOING TO BE A PROB. ATC ANSWERED, 'ABSOLUTELY NOT, NO PROB.' AUTOPLT #2 WAS THE CULPRIT. WE REENGAGED AUTOPLT #2 AT XA55 PDT. APPROX 1 MIN LATER WITH ALT HOLD ILLUMINATED, THE ACFT STARTED TO CLB. NO AURAL OR LIGHT WARNINGS OCCURRED. RETURNED TO AUTOPLT #1 FOR REMAINDER OF FLT. THIS WAS A REPEAT WRITE-UP WHICH WAS SIGNED OFF THE DAY BEFORE AS 'OPS (CHK) OK.'

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.