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.