Narrative:

During an instructional flight between lex and sdf, I deviated from an initial approach altitude while in VMC conditions but on an IFR flight plan. My company's training practices are to send the instructor and students to outstations and conduct training during layovers. My students and myself were on our 3RD day and on the afternoon training flight (3 hours, pm). We were returning from lex and were established on the localizer and had been cleared for the approach. We had been on duty for 9 hours and were completing 4.5 hours of flight instruction for the day, most of which had been in actual IFR conditions. I was flying and on the intercept altitude of 2500 MSL. After being cleared for and established the initial altitude was 2100 MSL until glide slope intercept or the LOM for the localizer only. I was not receiving the glide slope and was, I thought, crossing the LOM due to a faulty ADF swing and an erroneous DME fix by a student. We were in VMC and legal VFR conditions so I was descending to localizer minimums and by now I also had the runway/airport in sight. I questioned the tower controller concerning the glide slope and he noted my position and improper altitude. At this time the glide slope needle appeared to 'jump' from its apparently stuck position. There was no other aircraft involved and nothing dangerous evolved from the altitude incursion. I was aware of the ground and my position and assumed the 'ok' to proceed visually to the airport. I believe several factors contributed: 1) fatigue from monitoring students and aircraft position during actual IMC. 2) premature ADF needle swing for unknown reasons. 3) interruption of glide slope signal or stuck indicator. 4) being in VMC conditions and assuming the action of proceeding visually would suffice.

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Original NASA ASRS Text

Title: ALT DEVIATION. PREMATURE DESCENT ON SIMULATED INSTRUMENT APCH.

Narrative: DURING AN INSTRUCTIONAL FLT BETWEEN LEX AND SDF, I DEVIATED FROM AN INITIAL APCH ALT WHILE IN VMC CONDITIONS BUT ON AN IFR FLT PLAN. MY COMPANY'S TRAINING PRACTICES ARE TO SEND THE INSTRUCTOR AND STUDENTS TO OUTSTATIONS AND CONDUCT TRAINING DURING LAYOVERS. MY STUDENTS AND MYSELF WERE ON OUR 3RD DAY AND ON THE AFTERNOON TRAINING FLT (3 HRS, PM). WE WERE RETURNING FROM LEX AND WERE ESTABLISHED ON THE LOC AND HAD BEEN CLRED FOR THE APCH. WE HAD BEEN ON DUTY FOR 9 HRS AND WERE COMPLETING 4.5 HOURS OF FLT INSTRUCTION FOR THE DAY, MOST OF WHICH HAD BEEN IN ACTUAL IFR CONDITIONS. I WAS FLYING AND ON THE INTERCEPT ALT OF 2500 MSL. AFTER BEING CLRED FOR AND ESTABLISHED THE INITIAL ALT WAS 2100 MSL UNTIL GLIDE SLOPE INTERCEPT OR THE LOM FOR THE LOC ONLY. I WAS NOT RECEIVING THE GLIDE SLOPE AND WAS, I THOUGHT, XING THE LOM DUE TO A FAULTY ADF SWING AND AN ERRONEOUS DME FIX BY A STUDENT. WE WERE IN VMC AND LEGAL VFR CONDITIONS SO I WAS DESCENDING TO LOC MINIMUMS AND BY NOW I ALSO HAD THE RWY/ARPT IN SIGHT. I QUESTIONED THE TWR CTLR CONCERNING THE GLIDE SLOPE AND HE NOTED MY POSITION AND IMPROPER ALT. AT THIS TIME THE GLIDE SLOPE NEEDLE APPEARED TO 'JUMP' FROM ITS APPARENTLY STUCK POSITION. THERE WAS NO OTHER ACFT INVOLVED AND NOTHING DANGEROUS EVOLVED FROM THE ALT INCURSION. I WAS AWARE OF THE GND AND MY POSITION AND ASSUMED THE 'OK' TO PROCEED VISUALLY TO THE ARPT. I BELIEVE SEVERAL FACTORS CONTRIBUTED: 1) FATIGUE FROM MONITORING STUDENTS AND ACFT POSITION DURING ACTUAL IMC. 2) PREMATURE ADF NEEDLE SWING FOR UNKNOWN REASONS. 3) INTERRUPTION OF GLIDE SLOPE SIGNAL OR STUCK INDICATOR. 4) BEING IN VMC CONDITIONS AND ASSUMING THE ACTION OF PROCEEDING VISUALLY WOULD SUFFICE.

Data retrieved from NASA's ASRS site as of August 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.