FLC RAISED QUESTION AS TO THE LEGALITY OF THEIR FLT THAT OPERATED MORE THAN 50 MI OFFSHORE IN AN OVERWATER OP.

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MY CURRENT POS IS R SEAT; 757. FAIRLY NEW TO THE ACFT; WITH PAST EXPERIENCE 4 ENG TURBOJET. SUPERFICIALLY AWARE OF RESTRS PERTAINING TO OVERWATER FLT WITH 2 ENG ACFT; BUT OBVIOUSLY NOT FLUENT. WE WERE A 'RESERVE' CREW; ON AN ACFT THAT HAS DOMESTIC USE ONLY. THIS WAS A SPONTANEOUS FLT; ADDED ON WITH NO ADVANCE WARNING. IT WAS CLRLY UNFAMILIAR TERRITORY TO FLC AND TO THE DISPATCHER. THE FACT THAT THE ACFT MAY NOT BE LEGAL FOR OVERWATER DISPATCH WAS CONSIDERED; HOWEVER; IT WAS DISMISSED PREDICATED ON 121.161 (A); REGARDING BEING WITHIN 60 MINS OF A SUITABLE ARPT. AFTER THE FLT; THERE WAS SOME DISCUSSION AMONG OTHER FLCS AS TO THE LEGALITY OF THE FLT; QUOTING 121.161 (B). AS OF THIS WRITING; IT APPEARS THAT THE RTING WAS LEGAL (BEYOND 50 MI LIMIT OF SHORE); BUT STEPS ARE BEING TAKEN TO INSURE THAT IN THE FUTURE; THE CREWS AND DISPATCH ARE MADE MORE COMFORTABLE WITH REGS THAT ARE RARELY USED. SUPPLEMENTAL INFO FROM ACN 270584: ACFT OPERATED BEYOND 50 MI LIMIT OF SHORELINE; SUBSEQUENT DISCUSSION PERTAINING TO LEGALITY OF FLT. OPERATED B-727 FOR ANOTHER AIRLINE FOR SEVERAL YEARS OVER SAME RTE WITH NO QUESTION OF LEGALITY. TO INSURE COMPLIANCE; OPERATED RETURN TRIP OVER LAND; BRIEFED PLT UNION TO INITIATE MORE CLARIFICATION ON REG FROM COMPANY.