C172 PLT EXECUTES INST APCH WITHOUT THE ASSOCIATED APCH PLATE.

Narrative

DURING LET-DOWN IN IMC TO BFI; AND AFTER LISTENING TO ATIS AND DETERMINING APCH IN USE; I COULD NOT LOCATE THE APCH PLATE. I INFORMED THE CTLR OF THE SIT AND HE ASKED MY INTENTIONS. I TOLD HIM I WOULD EITHER NEED AN APCH TO RWY 13R (WHICH I HAD) OR VECTORS TO A VISUAL APCH. THE CTLR LATER ASKED IF I COULD ACCEPT VECTORS TO THE RWY 31L APCH WITH HIM MONITORING MY PROGRESS. I REPLIED THAT IF HE COULD GIVE ME THE FREQ AND 'DA;' I COULD ACCEPT IT. I GOT THE FREQ AND IDENTED THE LOC. THE GS FLAG WAS NOT VISIBLE; BUT IT BECAME CLR DURING THE APCH THE GS WAS INOP. I INFORMED THE CTLR OF THIS FACT AND TOLD THE CTLR I WOULD NEED THE LOC ONLY MINIMUMS. HE ISSUED THEM AND TOLD ME MY POS RELATIVE TO AN APCH FIX; HOWEVER WITHOUT THE PLATE I STILL DIDN'T REALLY KNOW WHERE I WAS WITH RESPECT TO MY DSCNT. AFTER REACHING A 4 MI FIX (VFR GPS) ON THE LOC; I ESTABLISHED A 500 FPM DSCNT AND ESTABLISHED APCH SPD. JUST AS I WAS ABOUT TO DECLARE A MISSED APCH TO GET BETTER SITUATIONAL AWARENESS OR PERHAPS GO ELSEWHERE; I BROKE OUT AND GOT THE ARPT IN SIGHT (APPROX 1000 FT AGL). I EXECUTED AN UNEVENTFUL LNDG. KEY FACTORS: 1) APCH PLATE MISSING. I SHOULD HAVE GONE ELSEWHERE. 2) GS FAILED WITHOUT LOSS OF IDENT OR FLAG. 3) STUDENT IN L SEAT: I TOOK CTLS TO INTERCEPT THE LOC; BUT DIDN'T FLY IT WELL DUE TO HIGH WORKLOAD; TRYING TO COME UP WITH A PLAN; AND TRYING TO FLY IT FROM THE R SEAT. 4) MISSING APCH PLATE WOULD HAVE BEEN MUCH LESS PROBLEMATIC IF THE GS HADN'T FAILED.