Narrative:

The flight was operating from nrt to sfo and was scheduled for 8 hours 50 mins flying time. Class ii navigation utilized 3 INS units, all operating in triple-mix. Approaching the sfo gateway fix and establishing radar contact with oakland, the radar controller advised that the flight was 20 mi north of track. All INS indications showed 'on track.' a xchk of a distant VOR station did show north of the gateway. At sfo a check of all INS units indicated that all units were within 'write-up' tolerance (3 mph plus 3 mi, in this case approximately 30 mi). All units were outside the parameters normally seen (2-5 mi) at the end of a flight of this length. Further examination of previous flts of that aircraft's logbook showed deviations greater than normal but within limits. Callback conversation with reporter revealed the following: reporter more or less repeated what was in his report. He seems to think that the width of the protected airspace suddenly reduces from 100 mi to 10 mi at the gateway. He said they are routinely picked up by ARTCC radar about 200 mi offshore.

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Original NASA ASRS Text

Title: RPTR QUESTIONS THE ADEQUACY OF SEPARATION PROVIDED BY INS ON LONG TRIPS. HE THINKS TOLERANCES MAY BE TOO LOOSE.

Narrative: THE FLT WAS OPERATING FROM NRT TO SFO AND WAS SCHEDULED FOR 8 HRS 50 MINS FLYING TIME. CLASS II NAV UTILIZED 3 INS UNITS, ALL OPERATING IN TRIPLE-MIX. APCHING THE SFO GATEWAY FIX AND ESTABLISHING RADAR CONTACT WITH OAKLAND, THE RADAR CTLR ADVISED THAT THE FLT WAS 20 MI N OF TRACK. ALL INS INDICATIONS SHOWED 'ON TRACK.' A XCHK OF A DISTANT VOR STATION DID SHOW N OF THE GATEWAY. AT SFO A CHK OF ALL INS UNITS INDICATED THAT ALL UNITS WERE WITHIN 'WRITE-UP' TOLERANCE (3 MPH PLUS 3 MI, IN THIS CASE APPROX 30 MI). ALL UNITS WERE OUTSIDE THE PARAMETERS NORMALLY SEEN (2-5 MI) AT THE END OF A FLT OF THIS LENGTH. FURTHER EXAMINATION OF PREVIOUS FLTS OF THAT ACFT'S LOGBOOK SHOWED DEVS GREATER THAN NORMAL BUT WITHIN LIMITS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR MORE OR LESS REPEATED WHAT WAS IN HIS RPT. HE SEEMS TO THINK THAT THE WIDTH OF THE PROTECTED AIRSPACE SUDDENLY REDUCES FROM 100 MI TO 10 MI AT THE GATEWAY. HE SAID THEY ARE ROUTINELY PICKED UP BY ARTCC RADAR ABOUT 200 MI OFFSHORE.

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.