Narrative:

We were assigned to fly the angels 2 FMS SID when departing lax. I was the PF. At 400 ft AGL, as per company procedure, I called for LNAV to be engaged. Approaching the second FMC fix, we were asked by departure control if we were flying the SID. The captain, who was the PNF, responded by saying that we were. Departure control then cleared us direct to peeve intersection. As we were over pevee intersection and in the turn to the east, the controller then asked if we were flying the trm transition. The captain said we were in the turn. We thought this all seemed strange so the captain immediately did another FMC position accuracy check. This check showed the FMC's to be at the accurate position. I had already gone to VOR navigation, just to be sure. As the flight progressed, we did several more accuracy checks. We found en route that with radio updating the FMC position was accurate. However, both IRS position were off by 5-9 mi. Upon arrival, a maintenance logbook entry was made for maintenance personnel. Looking back, I cannot think of anything else that could have been done to make the IRS's more accurate. When initializing them, I did so by using gate coordinates instead of the airport coordinates. The captain later stated that he doublechked accuracy while holding short of the departure runway. This appears to have been a maintenance problem that possibly affected our navigation performance in the departure phase. I say possibly because the controller never did inform us that we were not flying the SID as published. We assumed we were due to all indications as well as the multiple accuracy checks that were done.

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Original NASA ASRS Text

Title: DEP CTLR QUESTIONED THE FLC OF A B737-300 IF THEY WERE FLYING THE SID DURING CLBING THROUGH 3000 FT DURING DEP. THEY CONFIRMED THAT THEY WERE WHEN REFING THEIR FMC DISPLAY. HOWEVER, THEY SUBSEQUENTLY RECHKED THE ACCURACY OF THEIR NAV COMPUTER AND FOUND IT OK, BUT THAT THE IRS SYS SHOWED AN ERROR OF 5-9 MI.

Narrative: WE WERE ASSIGNED TO FLY THE ANGELS 2 FMS SID WHEN DEPARTING LAX. I WAS THE PF. AT 400 FT AGL, AS PER COMPANY PROC, I CALLED FOR LNAV TO BE ENGAGED. APCHING THE SECOND FMC FIX, WE WERE ASKED BY DEP CTL IF WE WERE FLYING THE SID. THE CAPT, WHO WAS THE PNF, RESPONDED BY SAYING THAT WE WERE. DEP CTL THEN CLRED US DIRECT TO PEEVE INTXN. AS WE WERE OVER PEVEE INTXN AND IN THE TURN TO THE E, THE CTLR THEN ASKED IF WE WERE FLYING THE TRM TRANSITION. THE CAPT SAID WE WERE IN THE TURN. WE THOUGHT THIS ALL SEEMED STRANGE SO THE CAPT IMMEDIATELY DID ANOTHER FMC POS ACCURACY CHK. THIS CHK SHOWED THE FMC'S TO BE AT THE ACCURATE POS. I HAD ALREADY GONE TO VOR NAV, JUST TO BE SURE. AS THE FLT PROGRESSED, WE DID SEVERAL MORE ACCURACY CHKS. WE FOUND ENRTE THAT WITH RADIO UPDATING THE FMC POS WAS ACCURATE. HOWEVER, BOTH IRS POS WERE OFF BY 5-9 MI. UPON ARR, A MAINT LOGBOOK ENTRY WAS MADE FOR MAINT PERSONNEL. LOOKING BACK, I CANNOT THINK OF ANYTHING ELSE THAT COULD HAVE BEEN DONE TO MAKE THE IRS'S MORE ACCURATE. WHEN INITIALIZING THEM, I DID SO BY USING GATE COORDINATES INSTEAD OF THE ARPT COORDINATES. THE CAPT LATER STATED THAT HE DOUBLECHKED ACCURACY WHILE HOLDING SHORT OF THE DEP RWY. THIS APPEARS TO HAVE BEEN A MAINT PROB THAT POSSIBLY AFFECTED OUR NAV PERFORMANCE IN THE DEP PHASE. I SAY POSSIBLY BECAUSE THE CTLR NEVER DID INFORM US THAT WE WERE NOT FLYING THE SID AS PUBLISHED. WE ASSUMED WE WERE DUE TO ALL INDICATIONS AS WELL AS THE MULTIPLE ACCURACY CHKS THAT WERE 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.