Narrative:

Prior to departure from anc for a flight to ord, the first officer became too ill to operate the trip. After several hours and 3 replacement pilots, the company assigned a deadheading captain (hereinafter referred to as, 'first officer') to perform the first officer duties. All 3 INS's were aligned to the anc ramp and waypoints were inserted and x-chked for the intended route to ord. After the aircraft was cleared to the first waypoint, the captain engaged the a autoplt to the #1 INS and climbed to assigned cruising altitude. Once level he left the flight deck for a few mins, and while gone yeg center cleared the flight, 'present position direct' yeg (waypoint #6). At the time the aircraft was in an area not covered by radar. The first officer programmed all 3 INS's '0-6,' after which the captain returned to his station. Approximately abeam position of interim waypoints were noted and logged on the flight plan. When the flight came back into radar coverage northeast of yxj, yeg center advised that the aircraft would not cross yeg on present heading. Xtrack on the #1 INS was checked at 32 NM left. After a new clearance was received, the INS was reset '0-6.' at that point it was observed that the navigation mode switch had been inadvertently left in the heading position. It was rest to INS and the aircraft turned to 30 dgs right to a new heading of 120 degrees. On landing at ord, the INS errors were: #1 was 24 NM, #2 was 10 NM, #3 was 7 NM. At no time was there any mention of a traffic conflict. I do feel that having 2 captain's flying together was a contributing factor.

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Original NASA ASRS Text

Title: HEADING TRACK DEVIATION ON AN INS DIRECT CLRNC.

Narrative: PRIOR TO DEP FROM ANC FOR A FLT TO ORD, THE F/O BECAME TOO ILL TO OPERATE THE TRIP. AFTER SEVERAL HRS AND 3 REPLACEMENT PLTS, THE COMPANY ASSIGNED A DEADHEADING CAPT (HEREINAFTER REFERRED TO AS, 'F/O') TO PERFORM THE F/O DUTIES. ALL 3 INS'S WERE ALIGNED TO THE ANC RAMP AND WAYPOINTS WERE INSERTED AND X-CHKED FOR THE INTENDED RTE TO ORD. AFTER THE ACFT WAS CLRED TO THE FIRST WAYPOINT, THE CAPT ENGAGED THE A AUTOPLT TO THE #1 INS AND CLBED TO ASSIGNED CRUISING ALT. ONCE LEVEL HE LEFT THE FLT DECK FOR A FEW MINS, AND WHILE GONE YEG CENTER CLRED THE FLT, 'PRESENT POS DIRECT' YEG (WAYPOINT #6). AT THE TIME THE ACFT WAS IN AN AREA NOT COVERED BY RADAR. THE F/O PROGRAMMED ALL 3 INS'S '0-6,' AFTER WHICH THE CAPT RETURNED TO HIS STATION. APPROX ABEAM POS OF INTERIM WAYPOINTS WERE NOTED AND LOGGED ON THE FLT PLAN. WHEN THE FLT CAME BACK INTO RADAR COVERAGE NE OF YXJ, YEG CENTER ADVISED THAT THE ACFT WOULD NOT CROSS YEG ON PRESENT HDG. XTRACK ON THE #1 INS WAS CHKED AT 32 NM LEFT. AFTER A NEW CLRNC WAS RECEIVED, THE INS WAS RESET '0-6.' AT THAT POINT IT WAS OBSERVED THAT THE NAV MODE SWITCH HAD BEEN INADVERTENTLY LEFT IN THE HDG POS. IT WAS REST TO INS AND THE ACFT TURNED TO 30 DGS RIGHT TO A NEW HDG OF 120 DEGS. ON LNDG AT ORD, THE INS ERRORS WERE: #1 WAS 24 NM, #2 WAS 10 NM, #3 WAS 7 NM. AT NO TIME WAS THERE ANY MENTION OF A TFC CONFLICT. I DO FEEL THAT HAVING 2 CAPT'S FLYING TOGETHER WAS A CONTRIBUTING FACTOR.

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.