AN F2000 CREW PROGRAMMED THE FMS FOR AN EXPECTED TRACK FOLLOWING ATC VECTORS BUT THE FINAL FMS COURSE FLOWN DID NOT MEET THE CLRED RTE AND THE ACFT APCHED A WARNING AREA.

Narrative

WE HAD JUST DEPARTED THE SNA ARPT AND WERE FLYING THE MUSEL SIX DEP HEADING TOWARD THE MUSEL INTXN. ATC TURNED US ON A 090 DEG VECTOR TO JOIN THE DEP PROC. THE NON-FLYING PLT THEN SET UP THE FMS TO PROVIDE COURSE GUIDANCE AFTER THE MUSEL INTXN SINCE THE ASSIGNED HDG WOULD TAKE US E OF MUSEL AND WOULD JOIN THE COURSE THERE. A SHORT TIME LATER; ATC TURNED US TO A 040 DEG HDG TO AVOID THE RESTRICTED AIRSPACE; R-2503C. APPARENTLY THE FMS SEQUENCED IN SUCH A MANNER TO DRAW A 071 DEG COURSE LINE FROM MUSEL DIRECTLY TO TRM (THERMAL) VOR INSTEAD OF A 061 DEG HDG COURSE LINE TO THE TEYKI INTXN AND THEN A 083 DEG HDG COURSE LINE TO TRM. THIS ERROR GOT US CLOSE TO THE RESTRICTED AIRSPACE AND ATC CAUGHT IT AND GAVE US THE HDG CORRECTION. BOTH I AND THE OTHER PLT WERE PERPLEXED AS TO WHY THE FMS SEQUENCED IN THE WAY IT DID INSTEAD OF THE EXPECTED SEQUENCE. THIS IS ANOTHER CASE OF THE AUTOMATION DOING SOMETHING NOT EXPECTED BY THE PLTS. IN RETROSPECT; WE SHOULD HAVE SET UP BACKUP VOR RAW DATA NEEDLES TO BACK UP THE FMS.