Narrative:

On departure out of lax I was flying. After liftoff and during the after takeoff checklist we realized we had a dual IRS failure (flags on attitude indicator and pdi card which gave us stuck cards on heading and attitude.' captain took over aircraft and flew by standby horizon and outside references. During this time lax departure called and told us to fly a 250 degree heading. (Both pdi showed 250 degrees, but were stuck.) the aircraft had drifted 30-40 degrees south of course. The captain pulled down the whiskey compass and complied with lax departures instructions. At this time, I went to att on both IRS's to reestablish our attitude and heading information in the FMC. We accomplished the above according to the approved air carrier abnormal procedures as per fom. Considering that our destination was VFR and we had reestablished both attitude, navigation aids and components, the captain elected to continue on to seattle. After arriving in seattle we reset the whole system and called maintenance control to report the problem. We had no further problems with either IRS unit for the next 2 legs. Callback conversation with reporter revealed the following: reporter states both systems failed simultaneously and for a period the flight crew was unsure of their exact position. No IRS situation or warning lights illuminated both IFR selectors were in the navigation mode. Reporter thinks that system fast align was used before this flight. Once aligned on the ground after arrival at destination both systems functioned completely normally and reporter knows of no further problems with aircraft.

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Original NASA ASRS Text

Title: TRACK DEVIATION. ACR ADVTECH MLG MAY HAVE EXPERIENCED DUAL IRS FAILURE.

Narrative: ON DEP OUT OF LAX I WAS FLYING. AFTER LIFTOFF AND DURING THE AFTER TKOF CHKLIST WE REALIZED WE HAD A DUAL IRS FAILURE (FLAGS ON ATTITUDE INDICATOR AND PDI CARD WHICH GAVE US STUCK CARDS ON HDG AND ATTITUDE.' CAPT TOOK OVER ACFT AND FLEW BY STANDBY HORIZON AND OUTSIDE REFERENCES. DURING THIS TIME LAX DEP CALLED AND TOLD US TO FLY A 250 DEG HDG. (BOTH PDI SHOWED 250 DEGS, BUT WERE STUCK.) THE ACFT HAD DRIFTED 30-40 DEGS S OF COURSE. THE CAPT PULLED DOWN THE WHISKEY COMPASS AND COMPLIED WITH LAX DEPS INSTRUCTIONS. AT THIS TIME, I WENT TO ATT ON BOTH IRS'S TO REESTABLISH OUR ATTITUDE AND HDG INFO IN THE FMC. WE ACCOMPLISHED THE ABOVE ACCORDING TO THE APPROVED ACR ABNORMAL PROCS AS PER FOM. CONSIDERING THAT OUR DEST WAS VFR AND WE HAD REESTABLISHED BOTH ATTITUDE, NAV AIDS AND COMPONENTS, THE CAPT ELECTED TO CONTINUE ON TO SEATTLE. AFTER ARRIVING IN SEATTLE WE RESET THE WHOLE SYS AND CALLED MAINT CTL TO RPT THE PROB. WE HAD NO FURTHER PROBS WITH EITHER IRS UNIT FOR THE NEXT 2 LEGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES BOTH SYSTEMS FAILED SIMULTANEOUSLY AND FOR A PERIOD THE FLT CREW WAS UNSURE OF THEIR EXACT POS. NO IRS SITUATION OR WARNING LIGHTS ILLUMINATED BOTH IFR SELECTORS WERE IN THE NAV MODE. RPTR THINKS THAT SYS FAST ALIGN WAS USED BEFORE THIS FLT. ONCE ALIGNED ON THE GND AFTER ARR AT DEST BOTH SYSTEMS FUNCTIONED COMPLETELY NORMALLY AND RPTR KNOWS OF NO FURTHER PROBS WITH ACFT.

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.