Narrative:

The flight pushed back on schedule, taxied to the runway, and was cleared for takeoff. As the aircraft entered the runway, the #5 and #6 annunciators illuminated on the flight engineer's anti-skid panel, accompanied by the anti-skid inoperative light on the pilot's panel. The aircraft was taxied clear of the runway and the all checklists were accomplished. Circuit breakers were checked and reset with no relief of the problem and the aircraft was taxied back to its origin, gate X. The anti-skid 'pig tails' on each truck were sprayed with contact cleaner and the anti-skid system was tested for fault illumination. The system tested normally, and the ground crew was alerted for an immediate pushback. A B747 was approximately 15 mins from scheduled departure, and the airport's one available tug had been positioned on that aircraft for their pushback. A significant cumulo nimbus cloud was approaching the departure end of the runway. I briefed the crew that we were near maximum gross weight for the runway, the outboard reversers were not available and we had the possibility of future anti-skid malfunctions. These items, coupled with a wet runway, created an urgency to depart prior to the storms arrival onto the runway area. The ground crew was urged for an immediate pushback. The tug was removed from the other aircraft and hastily repositioned to our aircraft. As the crew was accomplishing the before start checklist, the tug was connected to our nosegear and the aircraft was accidentally moved. Immediately, the 3 red warning lights illuminated on the INS mode panels. From reaction, I moved all 3 mode selectors to the navigation position and the red lights extinguished. All INS data selectors were placed to the dsrtk/sts position and the test buttons were pushed until all faults were cleared. Had the warning lights remained illuminated, or any faults remained in the system, then normal re-initialization would have been performed. However, all faults were cleared from the inu. All mileage and other indications appeared normal. Prior experience with INS system that were moved prior to selecting navigation, had always resulted in unusable system that required complete re-initialization. This system, which is different and more sophisticated than other aircraft in our fleet, cleared all faults and appeared completely normal. Because of the rapidly approaching WX, the perceived aircraft abnormalities, and what appeared to be a normal navigation system, the aircraft was launched. During departure the navigation system was monitored continuously and all indications appeared normal. Gross navigation error checks were plotted at 'kebar,' which is 107 mi from the departure airport. System #1 was 1.5 mi, system #2 was 2 mi, and system #3, 2 mi, total error. Perhaps slightly more 'error' than usual, but not out of tolerance. Further plots were performed, however the aircraft was constantly maneuvering due to heavy WX activity along the track. Permission was received from nan control for deviations up to 20 mi and this maneuvering contributed to the difficulty of precise plotting from the two available (1 NDB and 1 VOR) land navaids, thus eliminating a proper position update during the 1 hour after launch. During cruise, the INS system were continuously evaluated. After more than 4 hours of flight (past the etp), system #3 had acquired several faults that would not clear and differed in mileage by 15 mi, however track centerline was consistent with #1 and #2. System #1 was paralleling system #2 but their ctrlines was approximately 14 mi apart. System #1 led system #2 by 10 mi. Contingent navigation was maintained via computer flight plan magnetic headings, etc. Prior to anticipated VOR capture at hnl, the DME captured without azimuth and ZHN was called and notified of an apparent INS discrepancy. The flight was radar idented and recovered normally. We were advised by ZHN that we were approximately 20 mi off course. Recommendations: further training should be provided all crews concerning the specific INS installation aboard this aircraft. Emphasis should be made that re-initialization is always required after an aircraft movement prior to navigation selection, regardless of system indications.

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Original NASA ASRS Text

Title: GROSS NAV ERROR OCCURS WHEN THE FLC OF A NIGHT FREIGHTER FAILS TO INSURE PROPER ALIGNMENT OF THEIR 3 INERTIAL NAV SYS DURING PREFLT PROCS. ACFT WAS MOVED PREMATURELY BY TUG. WX FACTORS CONTRIBUTED TO RUSHED DEP.

Narrative: THE FLT PUSHED BACK ON SCHEDULE, TAXIED TO THE RWY, AND WAS CLRED FOR TKOF. AS THE ACFT ENTERED THE RWY, THE #5 AND #6 ANNUNCIATORS ILLUMINATED ON THE FE'S ANTI-SKID PANEL, ACCOMPANIED BY THE ANTI-SKID INOP LIGHT ON THE PLT'S PANEL. THE ACFT WAS TAXIED CLR OF THE RWY AND THE ALL CHKLISTS WERE ACCOMPLISHED. CIRCUIT BREAKERS WERE CHKED AND RESET WITH NO RELIEF OF THE PROB AND THE ACFT WAS TAXIED BACK TO ITS ORIGIN, GATE X. THE ANTI-SKID 'PIG TAILS' ON EACH TRUCK WERE SPRAYED WITH CONTACT CLEANER AND THE ANTI-SKID SYS WAS TESTED FOR FAULT ILLUMINATION. THE SYS TESTED NORMALLY, AND THE GND CREW WAS ALERTED FOR AN IMMEDIATE PUSHBACK. A B747 WAS APPROX 15 MINS FROM SCHEDULED DEP, AND THE ARPT'S ONE AVAILABLE TUG HAD BEEN POSITIONED ON THAT ACFT FOR THEIR PUSHBACK. A SIGNIFICANT CUMULO NIMBUS CLOUD WAS APCHING THE DEP END OF THE RWY. I BRIEFED THE CREW THAT WE WERE NEAR MAX GROSS WT FOR THE RWY, THE OUTBOARD REVERSERS WERE NOT AVAILABLE AND WE HAD THE POSSIBILITY OF FUTURE ANTI-SKID MALFUNCTIONS. THESE ITEMS, COUPLED WITH A WET RWY, CREATED AN URGENCY TO DEPART PRIOR TO THE STORMS ARR ONTO THE RWY AREA. THE GND CREW WAS URGED FOR AN IMMEDIATE PUSHBACK. THE TUG WAS REMOVED FROM THE OTHER ACFT AND HASTILY REPOSITIONED TO OUR ACFT. AS THE CREW WAS ACCOMPLISHING THE BEFORE START CHKLIST, THE TUG WAS CONNECTED TO OUR NOSEGEAR AND THE ACFT WAS ACCIDENTALLY MOVED. IMMEDIATELY, THE 3 RED WARNING LIGHTS ILLUMINATED ON THE INS MODE PANELS. FROM REACTION, I MOVED ALL 3 MODE SELECTORS TO THE NAV POS AND THE RED LIGHTS EXTINGUISHED. ALL INS DATA SELECTORS WERE PLACED TO THE DSRTK/STS POS AND THE TEST BUTTONS WERE PUSHED UNTIL ALL FAULTS WERE CLRED. HAD THE WARNING LIGHTS REMAINED ILLUMINATED, OR ANY FAULTS REMAINED IN THE SYS, THEN NORMAL RE-INITIALIZATION WOULD HAVE BEEN PERFORMED. HOWEVER, ALL FAULTS WERE CLRED FROM THE INU. ALL MILEAGE AND OTHER INDICATIONS APPEARED NORMAL. PRIOR EXPERIENCE WITH INS SYS THAT WERE MOVED PRIOR TO SELECTING NAV, HAD ALWAYS RESULTED IN UNUSABLE SYS THAT REQUIRED COMPLETE RE-INITIALIZATION. THIS SYS, WHICH IS DIFFERENT AND MORE SOPHISTICATED THAN OTHER ACFT IN OUR FLEET, CLRED ALL FAULTS AND APPEARED COMPLETELY NORMAL. BECAUSE OF THE RAPIDLY APCHING WX, THE PERCEIVED ACFT ABNORMALITIES, AND WHAT APPEARED TO BE A NORMAL NAV SYS, THE ACFT WAS LAUNCHED. DURING DEP THE NAV SYS WAS MONITORED CONTINUOUSLY AND ALL INDICATIONS APPEARED NORMAL. GROSS NAV ERROR CHKS WERE PLOTTED AT 'KEBAR,' WHICH IS 107 MI FROM THE DEP ARPT. SYS #1 WAS 1.5 MI, SYS #2 WAS 2 MI, AND SYS #3, 2 MI, TOTAL ERROR. PERHAPS SLIGHTLY MORE 'ERROR' THAN USUAL, BUT NOT OUT OF TOLERANCE. FURTHER PLOTS WERE PERFORMED, HOWEVER THE ACFT WAS CONSTANTLY MANEUVERING DUE TO HVY WX ACTIVITY ALONG THE TRACK. PERMISSION WAS RECEIVED FROM NAN CTL FOR DEVS UP TO 20 MI AND THIS MANEUVERING CONTRIBUTED TO THE DIFFICULTY OF PRECISE PLOTTING FROM THE TWO AVAILABLE (1 NDB AND 1 VOR) LAND NAVAIDS, THUS ELIMINATING A PROPER POS UPDATE DURING THE 1 HR AFTER LAUNCH. DURING CRUISE, THE INS SYS WERE CONTINUOUSLY EVALUATED. AFTER MORE THAN 4 HRS OF FLT (PAST THE ETP), SYS #3 HAD ACQUIRED SEVERAL FAULTS THAT WOULD NOT CLR AND DIFFERED IN MILEAGE BY 15 MI, HOWEVER TRACK CTRLINE WAS CONSISTENT WITH #1 AND #2. SYS #1 WAS PARALLELING SYS #2 BUT THEIR CTRLINES WAS APPROX 14 MI APART. SYS #1 LED SYS #2 BY 10 MI. CONTINGENT NAV WAS MAINTAINED VIA COMPUTER FLT PLAN MAGNETIC HEADINGS, ETC. PRIOR TO ANTICIPATED VOR CAPTURE AT HNL, THE DME CAPTURED WITHOUT AZIMUTH AND ZHN WAS CALLED AND NOTIFIED OF AN APPARENT INS DISCREPANCY. THE FLT WAS RADAR IDENTED AND RECOVERED NORMALLY. WE WERE ADVISED BY ZHN THAT WE WERE APPROX 20 MI OFF COURSE. RECOMMENDATIONS: FURTHER TRAINING SHOULD BE PROVIDED ALL CREWS CONCERNING THE SPECIFIC INS INSTALLATION ABOARD THIS ACFT. EMPHASIS SHOULD BE MADE THAT RE-INITIALIZATION IS ALWAYS REQUIRED AFTER AN ACFT MOVEMENT PRIOR TO NAV SELECTION, REGARDLESS OF SYS INDICATIONS.

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.