Narrative:

Flight was a scheduled air carrier segment from hnl-kix (osaka/kansai). Preflight checks were normal. Both captain and first officer HSI and RMI agreed within +/- 3 degrees. Captain HSI and first officer RMI compasses are fed by #1 inertial navigation. First officer's HSI and captain's RMI are driven by #2 inertial. On taxi out, HSI's and RMI's once again were within limits, as per company procedures. After the taxi check, the DC10 conducted 2 90-degree turns en route to the hold position on the active runway (runway 8R). The aircraft sat in position for approximately 1 min awaiting a departure sequence. Neither the captain, so, nor myself noticed or checked the HSI/RMI versus runway heading. When we received our takeoff clearance, our departure heading was modified from 155 degrees to 140 degrees -- the initial altitude remained unchanged at 5000 ft. After the wheels were up and climbing through 500 ft AGL, a right turn was commenced. After initial check-in with departure control (with included assigned altitude of 5000 ft and heading 140 degrees), I noticed something didn't look right on my HSI. We had already turned about 50 degrees and my heading was only about 090 degrees. About 1/2 way into the turn ATC questioned our assigned heading. I responded we were turning right to 140 degrees. At about the same time the so noticed both HSI's/RMI's deferred from the wet compass by about 50 degrees. ATC told us to turn left and level at 2500 ft. We complied. Apparently, a cessna was sharing the same airspace at 3000 ft. We received 1 'traffic' call on our TCASII, but no RA. Once we were steadied up on a 140 degree magnetic heading, the so resynced both inertial compass slave selectors to the proper heading. We were subsequently cleared to 3000 ft and on up to FL280. In my 20+ yrs of flying I have never seen both inertial headings precess in the same direction, to the same heading, and by such a large amount (50 degrees). I'm not sure when the precession occurred, but our failure to make a final heading check prior to starting the takeoff roll probably contributed to this deviation. Supplemental information from acn 393739: departure issued climb to FL280, followed by say your heading. We responded, turning right to 140 degrees (heading was 120 degrees). Controller said, stop turn and maintain 2500 ft, which I did. Error must have occurred some time between taxi out check and climb. Back to basics -- confirm compass heading with departure runway! ATC gets credit for a job well done.

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Original NASA ASRS Text

Title: A DC10 DEPARTING HNL OVERSHOT ITS ASSIGNED HDG ON INITIAL CLB. DEP CTLR NOTES ERROR AND STOPS TURN AND CLB TO AVERT ANY FURTHER LOSS OF SEPARATION FROM A NEARBY CESSNA AT 3000 FT. THE ACFT'S HSI'S AND RMI'S HAD BOTH PRECESSED APPROX 40 DEGS FROM CORRECT SENSING.

Narrative: FLT WAS A SCHEDULED ACR SEGMENT FROM HNL-KIX (OSAKA/KANSAI). PREFLT CHKS WERE NORMAL. BOTH CAPT AND FO HSI AND RMI AGREED WITHIN +/- 3 DEGS. CAPT HSI AND FO RMI COMPASSES ARE FED BY #1 INERTIAL NAV. FO'S HSI AND CAPT'S RMI ARE DRIVEN BY #2 INERTIAL. ON TAXI OUT, HSI'S AND RMI'S ONCE AGAIN WERE WITHIN LIMITS, AS PER COMPANY PROCS. AFTER THE TAXI CHK, THE DC10 CONDUCTED 2 90-DEG TURNS ENRTE TO THE HOLD POS ON THE ACTIVE RWY (RWY 8R). THE ACFT SAT IN POS FOR APPROX 1 MIN AWAITING A DEP SEQUENCE. NEITHER THE CAPT, SO, NOR MYSELF NOTICED OR CHKED THE HSI/RMI VERSUS RWY HDG. WHEN WE RECEIVED OUR TKOF CLRNC, OUR DEP HDG WAS MODIFIED FROM 155 DEGS TO 140 DEGS -- THE INITIAL ALT REMAINED UNCHANGED AT 5000 FT. AFTER THE WHEELS WERE UP AND CLBING THROUGH 500 FT AGL, A R TURN WAS COMMENCED. AFTER INITIAL CHK-IN WITH DEP CTL (WITH INCLUDED ASSIGNED ALT OF 5000 FT AND HDG 140 DEGS), I NOTICED SOMETHING DIDN'T LOOK RIGHT ON MY HSI. WE HAD ALREADY TURNED ABOUT 50 DEGS AND MY HDG WAS ONLY ABOUT 090 DEGS. ABOUT 1/2 WAY INTO THE TURN ATC QUESTIONED OUR ASSIGNED HDG. I RESPONDED WE WERE TURNING R TO 140 DEGS. AT ABOUT THE SAME TIME THE SO NOTICED BOTH HSI'S/RMI'S DEFERRED FROM THE WET COMPASS BY ABOUT 50 DEGS. ATC TOLD US TO TURN L AND LEVEL AT 2500 FT. WE COMPLIED. APPARENTLY, A CESSNA WAS SHARING THE SAME AIRSPACE AT 3000 FT. WE RECEIVED 1 'TFC' CALL ON OUR TCASII, BUT NO RA. ONCE WE WERE STEADIED UP ON A 140 DEG MAGNETIC HDG, THE SO RESYNCED BOTH INERTIAL COMPASS SLAVE SELECTORS TO THE PROPER HDG. WE WERE SUBSEQUENTLY CLRED TO 3000 FT AND ON UP TO FL280. IN MY 20+ YRS OF FLYING I HAVE NEVER SEEN BOTH INERTIAL HDGS PRECESS IN THE SAME DIRECTION, TO THE SAME HDG, AND BY SUCH A LARGE AMOUNT (50 DEGS). I'M NOT SURE WHEN THE PRECESSION OCCURRED, BUT OUR FAILURE TO MAKE A FINAL HDG CHK PRIOR TO STARTING THE TKOF ROLL PROBABLY CONTRIBUTED TO THIS DEV. SUPPLEMENTAL INFO FROM ACN 393739: DEP ISSUED CLB TO FL280, FOLLOWED BY SAY YOUR HDG. WE RESPONDED, TURNING R TO 140 DEGS (HDG WAS 120 DEGS). CTLR SAID, STOP TURN AND MAINTAIN 2500 FT, WHICH I DID. ERROR MUST HAVE OCCURRED SOME TIME BTWN TAXI OUT CHK AND CLB. BACK TO BASICS -- CONFIRM COMPASS HDG WITH DEP RWY! ATC GETS CREDIT FOR A JOB WELL DONE.

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.