F100 CREW WAS REQUIRED TO FLY A SURVEILLANCE APCH 'ASR' TO RWY 24 AT BHM BECAUSE THE ILS GS FAILED.

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ENRTE WX HAD BEEN GOOD; BUT AN AREA OF RAIN SHOWERS AND TSTMS WERE IN THE VICINITY OF BHM AND EXTENDED E FROM THERE. BHM ATIS INDICATED LIGHT WINDS AND RWY 6; BUT OUR WX RADAR INDICATED A STORM ON THE APCH TO RWY 6. ON INITIAL CONTACT; BHM APCH CONFIRMED THE STORM ON APCH TO RWY 6 AND ADVISED US TO PLAN THE ILS TO RWY 24. THAT APCH WAS GENERALLY CLR OF STORMS -- ALTHOUGH SUBSTANTIAL MANEUVERING WOULD BE REQUIRED TO REMAIN CLR OF WX WHILE APCHING THE INTERCEPT POINT. THE ACFT AHEAD OF US USED A WX-FREE CORRIDOR FOR A WIDE R BASE AND ACCEPTED CLRNC FOR THE ILS TO RWY 24. WE PLANNED TO FOLLOW HIS PATH THROUGH THE SAME CORRIDOR. ESTABLISHED ON THE ILS; THE ACFT AHEAD ANNOUNCED THAT THE LOC AND GS HAD SUDDENLY FAILED. APCH CTL OFFERED HIM A SURVEILLANCE APCH; WHICH HE ACCEPTED AND COMPLETED. LIKEWISE; THEY OFFERED US A SURVEILLANCE APCH. I WILL TELL YOU THAT ON PERHAPS A 15 MI R BASE IN A STORM-FREE CORRIDOR AND WITH A STORM-FREE FINAL; BUT WITH STORMS IN ALL OTHER QUADRANTS -- ANSWERING THE QUESTION; 'ARE WE ALLOWED TO ACCEPT A SURVEILLANCE APCH?' IS A DICEY PROB TO SOLVE AT BEST. A RUSHED THUMBING THROUGH COMPANY FOM APCH/LNDG SECTION MADE IT FAIRLY CLR THAT WE COULD ACCEPT THE OFFER. WE FLEW THE APCH; CONCERNED PRIMARILY WITH THE BEST 'ESCAPE' RTE IN THE EVENT WE HAD TO MISS (WX ALONG THE STRAIGHT-AHEAD MISS CORRIDOR; RIDGE LINES ALONG EITHER SIDE). THE APCH WAS COMFORTABLE AND RESULTED IN AN UNEVENTFUL LNDG ON RWY 24. IN ABOUT 1 HR; WHILE REVIEWING FLT MANUAL; I CHANCED ACROSS SECTION X WHICH DESCRIBES THE SURVEILLANCE APCH IN MUCH THE SAME TERMS AS IN THE OPERATING MANUAL; EXCEPT FOR ONE THING. A PARAGRAPH HAS BEEN RECENTLY ADDED INDICATING THAT THESE APCHS ARE NOT AUTHORIZED EXCEPT IN AN EMER. OUR SIT MAY HAVE BEEN A BIT DICEY; BUT IT WAS CERTAINLY NO EMER. I'M STILL INCLINED TO THINK THAT UNDER THE PARTICULAR CONDITIONS THAT EXISTED THERE THAT DAY; THE BEST AND SAFEST CHOICE WAS THE CHOICE I MADE -- EVEN IF IT WASN'T ABSOLUTELY 'KOSHER.' SINCE SURVEILLANCE APCHS ARE APPARENTLY NO LONGER ACCEPTABLE UNDER OUR OPERATING SPECS; I URGE THAT THE OPERATING MANUAL BE 'ADJUSTED' TO CLARIFY THIS FACT MUCH AS THE PROHIBITION AGAINST BACK COURSE APCHS IS MADE ABUNDANTLY CLR.