Narrative:

On takeoff from runway 1R at sfo, the sfo 8 departure calls for a right turn to a 030 degree heading. Both compass system were off by 25 degrees (with no flags), so that when I went to turn at 500 ft, a heading of 030 degrees was actually a left turn of 5 degrees. We knew something wasn't right, so we compared compass system #1 and #2 with the standby (wet) compass and by 1000 ft we were turning the desired direction toward oakland airport. In the turn, bay departure must have noticed our delayed turn and cleared us to maintain heading 030 degrees. Later they asked us if we were cleared on the sfo 8 departure, and we responded in the affirmative, but that we had a gyro compass problem and we were troubleshooting. We used the compass system #1 and #2 fast slew knob to match our headings with the standby compass and the headings indicated normal the remainder of the flight. We could not recall the indicated heading during the taxi check (should have been 192 degrees on taxiway a), but our responses showed our instruments did match. Normally at least 1 compass system reads inaccurately at the gate because the jetway and ground equipment interferes with the flux valves in the wing. Most likely, both compass system read the same on taxi out, but both had the same error of about 25 degrees created while sitting at the gate. Our taxi time of 16 mins evidently was not long enough to automatically slew to the correct heading. In summary, it is not enough to compare compass system #1 versus #2, you must compare your instruments with a known heading or a standby compass. Supplemental information from acn 504271: both gyros failed to synchronize for takeoff for approximately 25 degrees off course indication. During sfo 8 departure, the heading of 030 degrees was flown on our HSI for 1-2 mi until troubleshooting determined that our gyro was off 25 degrees. Controller did query the crew and an immediate 20 degree turn to right was commenced to make us back on course. No traffic conflict occurred. Logbook maintenance write-up followed. Indications were normal the remainder of the flight. Supplemental information from acn 504765: on taxi out from sfo, captain and first officer both read same heading as we checked the heading cards. (I read the checklist.) both headings were off by 30 degrees. After takeoff, we realized the problem when they turned the wrong way! Should have matched headings with the runway!

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Original NASA ASRS Text

Title: A DC10 CREW, ON DEP, TURNED TO THE WRONG HDG DUE TO A 25 DEG ERROR IN THE COMPASS SYS.

Narrative: ON TKOF FROM RWY 1R AT SFO, THE SFO 8 DEP CALLS FOR A R TURN TO A 030 DEG HDG. BOTH COMPASS SYS WERE OFF BY 25 DEGS (WITH NO FLAGS), SO THAT WHEN I WENT TO TURN AT 500 FT, A HDG OF 030 DEGS WAS ACTUALLY A L TURN OF 5 DEGS. WE KNEW SOMETHING WASN'T RIGHT, SO WE COMPARED COMPASS SYS #1 AND #2 WITH THE STANDBY (WET) COMPASS AND BY 1000 FT WE WERE TURNING THE DESIRED DIRECTION TOWARD OAKLAND ARPT. IN THE TURN, BAY DEP MUST HAVE NOTICED OUR DELAYED TURN AND CLRED US TO MAINTAIN HDG 030 DEGS. LATER THEY ASKED US IF WE WERE CLRED ON THE SFO 8 DEP, AND WE RESPONDED IN THE AFFIRMATIVE, BUT THAT WE HAD A GYRO COMPASS PROB AND WE WERE TROUBLESHOOTING. WE USED THE COMPASS SYS #1 AND #2 FAST SLEW KNOB TO MATCH OUR HDGS WITH THE STANDBY COMPASS AND THE HDGS INDICATED NORMAL THE REMAINDER OF THE FLT. WE COULD NOT RECALL THE INDICATED HDG DURING THE TAXI CHK (SHOULD HAVE BEEN 192 DEGS ON TXWY A), BUT OUR RESPONSES SHOWED OUR INSTS DID MATCH. NORMALLY AT LEAST 1 COMPASS SYS READS INACCURATELY AT THE GATE BECAUSE THE JETWAY AND GND EQUIP INTERFERES WITH THE FLUX VALVES IN THE WING. MOST LIKELY, BOTH COMPASS SYS READ THE SAME ON TAXI OUT, BUT BOTH HAD THE SAME ERROR OF ABOUT 25 DEGS CREATED WHILE SITTING AT THE GATE. OUR TAXI TIME OF 16 MINS EVIDENTLY WAS NOT LONG ENOUGH TO AUTOMATICALLY SLEW TO THE CORRECT HDG. IN SUMMARY, IT IS NOT ENOUGH TO COMPARE COMPASS SYS #1 VERSUS #2, YOU MUST COMPARE YOUR INSTS WITH A KNOWN HDG OR A STANDBY COMPASS. SUPPLEMENTAL INFO FROM ACN 504271: BOTH GYROS FAILED TO SYNCHRONIZE FOR TKOF FOR APPROX 25 DEGS OFF COURSE INDICATION. DURING SFO 8 DEP, THE HDG OF 030 DEGS WAS FLOWN ON OUR HSI FOR 1-2 MI UNTIL TROUBLESHOOTING DETERMINED THAT OUR GYRO WAS OFF 25 DEGS. CTLR DID QUERY THE CREW AND AN IMMEDIATE 20 DEG TURN TO R WAS COMMENCED TO MAKE US BACK ON COURSE. NO TFC CONFLICT OCCURRED. LOGBOOK MAINT WRITE-UP FOLLOWED. INDICATIONS WERE NORMAL THE REMAINDER OF THE FLT. SUPPLEMENTAL INFO FROM ACN 504765: ON TAXI OUT FROM SFO, CAPT AND FO BOTH READ SAME HDG AS WE CHKED THE HDG CARDS. (I READ THE CHKLIST.) BOTH HDGS WERE OFF BY 30 DEGS. AFTER TKOF, WE REALIZED THE PROB WHEN THEY TURNED THE WRONG WAY! SHOULD HAVE MATCHED HDGS WITH THE RWY!

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.