A BE99 TRAINING FLT ABORTS ITS APCH WHEN TWR ADVISES THEM OF A LOW ALT ALERT WHEN INSIDE THE LOM FOR RWY 25 AT OXR; CA.

Narrative

I WAS A TRAINING CAPT IN COMMAND OF A TRAINING FLT FROM BUR TO OXR. FLT PLAN WAS IFR AND WE WERE ON AN IFR CLRNC; CLRED FOR THE ILS RWY 25 OXR. I WAS PNF IN THE R SEAT. I HAD SIMULATED AN ENG FAILURE ON THE ILS AND WAS MONITORING MY TRAINEE'S PROGRESS WHILE ALSO LOOKING FOR TFC. I WAS APPROX 70% HEAD OUTSIDE COCKPIT AND 30% HEAD INSIDE TO MONITOR HIS PERFORMANCE. MEANWHILE; THE #1 HSI GS HAD FAILED IN THE CTR 'ON GS' INDICATION WITHOUT A CORRESPONDING FLAG OR BAR TO INDICATE OTHERWISE. IN THE PROX OF CMA VOR (OR CLOSE TO THIS OM) WE WERE ASSIGNED A FREQ CHANGE FROM MAGU APCH TO OXR TWR. AT ABOUT THIS TIME I SAW CMA ARPT AND SIMULTANEOUSLY GLANCED AT OUR ALT. WE WERE INDICATING APPROX 1600 FT MSL. WE SHOULD HAVE BEEN AT APPROX 2000 FT MSL. OXR TWR ISSUED A LOW ALT ALERT AND A CLB AND WERE ISSUED A FREQ CHANGE TO MAGU APCH. WE COMPLIED AND ONCE ON MAGU'S FREQ; I RPTED THE GS FAILURE (OUR EQUIP) AND CANCELED IFR. IN RETROSPECT; BOTH MY STUDENT AND I SHOULD HAVE CONTINUOUSLY XCHKED GS INDICATIONS WITH CHARTED ALTS (ON GS AT AND PRIOR TO THE OM).