AN ACR LGT CLBED IN RESPONSE TO A GPWS WARNING AT GEG ON THE CAT II ILS.

Narrative

WHILE BEING VECTORED FOR THE ILS RWY 21 CAT II APCH AT SPOKANE; WA (GEG); THE GPWS WENT OFF SOUNDING 'TERRAIN; TERRAIN....' AT THE TIME WE WERE IN NIGHT IMC AT 7000 FT MSL AND TALKING TO THE GEG APCH CTLR. WE IMMEDIATELY INITIATED THE GPWS ESCAPE MANEUVER CLBING TO 8500 FT AND SIMULTANEOUSLY NOTIFIED GEG APCH CTL RADAR OF OUR ACTIONS. THEY INDICATED THAT IT WAS NOT A UNIQUE OCCURRENCE AND THAT MICA PEAK WAS LOCATED NEARBY. ON THE SPOKANE; WASHINGTON AREA CHART COMMERCIAL PAGE 10-1 DATED MAY/X/91. THE AREA MINIMUM ALT (AMA) ENVELOPE (SEE COMMERCIAL INTRODUCTION PAGE 72 DATED 6/X/89) SHOWS A REF POINT CLRNC ALT OF 7400 FT MSL; WHICH IS 2000 FT ABOVE THE HIGHEST OBSTACLE IN THE AREA. ASSUMING WE WERE DIRECTLY OVERHEAD THAT OBSTACLE; WE CLRED IT BY 1600 FT. WHILE THIS MAY BE A SATISFACTORY MINIMUM VECTORING ALT AS FAR AS THE FAA IS CONCERNED; I DO NOT BELIEVE THAT IT IS APPROPRIATE IN NIGHT IMC WX. WE WERE LUCKILY ABLE TO REESTABLISH OURSELVES ON THE APCH AND THANKFULLY NO OTHER ACFT WERE ABOVE US BUT THE RADAR VECTORING AND ALT RESTRICTIONS SHOULD PREVENT THIS OCCURRENCE FROM HAPPENING AGAIN.