Narrative:

I was a training captain in command of a training flight from bur to oxr. Flight plan was IFR and we were on an IFR clearance, cleared for the ILS runway 25 oxr. I was PNF in the right seat. I had simulated an engine failure on the ILS and was monitoring my trainee's progress while also looking for traffic. I was approximately 70% head outside cockpit and 30% head inside to monitor his performance. Meanwhile, the #1 HSI GS had failed in the center 'on GS' indication without a corresponding flag or bar to indicate otherwise. In the proximity of cma VOR (or close to this OM) we were assigned a frequency change from magu approach to oxr tower. At about this time I saw cma airport and simultaneously glanced at our altitude. We were indicating approximately 1600 ft MSL. We should have been at approximately 2000 ft MSL. Oxr tower issued a low altitude alert and a climb and were issued a frequency change to magu approach. We complied and once on magu's frequency, I reported the GS failure (our equipment) and canceled IFR. In retrospect, both my student and I should have continuously crosschecked GS indications with charted altitudes (on GS at and prior to the OM).

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Original NASA ASRS Text

Title: 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).

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.