Track deviation over the north atlantic when unannunciated autoplt failure was not caught in a timel...

Attributes
ACN	490060
Time
Date	200010
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : czqx.artcc
State Reference	FO
Altitude	msl single value : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czqx.artcc tower : bwi.tower
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : atlantic
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 7500
ASRS Report	490060
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe non adherence : company policies other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended or assigned course
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While cruising over the north atlantic, we experienced an unannunciated autoplt failure which was not immediately detected by the crew, resulting in departure from our desired flight track. The first indication the crew noticed was a change in the sun's position in the windscreen. Upon checking raw data indicators (we were off course) we attempted to return to course using the autoplt, but it would not respond to inputs. The second autoplt was selected and the aircraft returned to proper track. The malfunctioning autoplt maintained a barely perceptible right bank resulting in a turn rate that was not immediately perceptible. The flight management indicators erroneously portrayed on course/on track. We could have minimized the impact of this malfunction by x-chking the raw data more frequently and not relying solely on our flight management displays.

Original NASA ASRS Text

Title: TRACK DEV OVER THE NORTH ATLANTIC WHEN UNANNUNCIATED AUTOPLT FAILURE WAS NOT CAUGHT IN A TIMELY MANNER.

Narrative: WHILE CRUISING OVER THE NORTH ATLANTIC, WE EXPERIENCED AN UNANNUNCIATED AUTOPLT FAILURE WHICH WAS NOT IMMEDIATELY DETECTED BY THE CREW, RESULTING IN DEP FROM OUR DESIRED FLT TRACK. THE FIRST INDICATION THE CREW NOTICED WAS A CHANGE IN THE SUN'S POS IN THE WINDSCREEN. UPON CHKING RAW DATA INDICATORS (WE WERE OFF COURSE) WE ATTEMPTED TO RETURN TO COURSE USING THE AUTOPLT, BUT IT WOULD NOT RESPOND TO INPUTS. THE SECOND AUTOPLT WAS SELECTED AND THE ACFT RETURNED TO PROPER TRACK. THE MALFUNCTIONING AUTOPLT MAINTAINED A BARELY PERCEPTIBLE R BANK RESULTING IN A TURN RATE THAT WAS NOT IMMEDIATELY PERCEPTIBLE. THE FLT MGMNT INDICATORS ERRONEOUSLY PORTRAYED ON COURSE/ON TRACK. WE COULD HAVE MINIMIZED THE IMPACT OF THIS MALFUNCTION BY X-CHKING THE RAW DATA MORE FREQUENTLY AND NOT RELYING SOLELY ON OUR FLT MGMNT DISPLAYS.

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.

Track deviation over the north atlantic when unannunciated autoplt failure was not caught in a timely manner.