Heading track deviation on a direct after INS input on amended clearance route change.

Attributes
ACN	186185
Time
Date	199108
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zau
State Reference	IL
Altitude	msl bound lower : 37000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	Heavy Transport, Low Wing, 4 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : direct
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 : 15000 flight time type : 150
ASRS Report	186185
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was en route from sfo to iad. In chicago center area we were cleared INS direct bradford VOR from our present position, at approximately PM35Z. I changed INS to 0 to 8 (present position 0, bradford VOR 8), and inserted. First officer monitored change. Autoplt was in 'auxiliary navigation' mode (INS) and changed heading for course direct bradford. Approximately 20 mins later I checked our position in relation to an intermediate VOR abeam, and relationship did not seem proper. Checked xtk/tke mode of INS, and we were 42 NM left of intended track. Discovered that autoplt had switched, at an unknown time, from 'auxiliary navigation' to 'turn knob' position and aircraft had wandered, due to xwinds. ATC was never involved with our situation, and we returned aircraft to course for bradford VOR. Rest of trip uneventful, autoplt operation satisfactory. I feel that autoplt design that allows selector to pop from 'auxiliary navigation' to 'turn knob' without aural or visual warning is unsatisfactory.

Original NASA ASRS Text

Title: HDG TRACK DEV ON A DIRECT AFTER INS INPUT ON AMENDED CLRNC RTE CHANGE.

Narrative: ACFT WAS ENRTE FROM SFO TO IAD. IN CHICAGO CENTER AREA WE WERE CLRED INS DIRECT BRADFORD VOR FROM OUR PRESENT POS, AT APPROX PM35Z. I CHANGED INS TO 0 TO 8 (PRESENT POS 0, BRADFORD VOR 8), AND INSERTED. FO MONITORED CHANGE. AUTOPLT WAS IN 'AUX NAV' MODE (INS) AND CHANGED HDG FOR COURSE DIRECT BRADFORD. APPROX 20 MINS LATER I CHKED OUR POS IN RELATION TO AN INTERMEDIATE VOR ABEAM, AND RELATIONSHIP DID NOT SEEM PROPER. CHKED XTK/TKE MODE OF INS, AND WE WERE 42 NM L OF INTENDED TRACK. DISCOVERED THAT AUTOPLT HAD SWITCHED, AT AN UNKNOWN TIME, FROM 'AUX NAV' TO 'TURN KNOB' POS AND ACFT HAD WANDERED, DUE TO XWINDS. ATC WAS NEVER INVOLVED WITH OUR SITUATION, AND WE RETURNED ACFT TO COURSE FOR BRADFORD VOR. REST OF TRIP UNEVENTFUL, AUTOPLT OP SATISFACTORY. I FEEL THAT AUTOPLT DESIGN THAT ALLOWS SELECTOR TO POP FROM 'AUX NAV' TO 'TURN KNOB' WITHOUT AURAL OR VISUAL WARNING IS UNSATISFACTORY.

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.