Small aircraft on localizer approach begins descent to MDA prior to passage of final approach fix.

Attributes
ACN	256999
Time
Date	199311
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : act
State Reference	TX
Altitude	msl bound lower : 1400 msl bound upper : 2300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : act
Make Model Name	Small Aircraft
Flight Phase	descent : approach
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 120 flight time total : 1570 flight time type : 308
ASRS Report	256999
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was inbound on the ILS 17L, outside the OM (leroi). The problem came about when the ADF needle swing to the from indication. The problem was discovered when I was descending to the MDA of 860 MSL, when I was at about 1400 MSL. I immediately started a climb back to 2300 MSL. The contributing factors to this were improper xchk of leroi using the 055 radial of waco VOR, also not receiving an oral or marker beacon light or waiting for the GS to come in. The reason I left the altitude of 2300 MSL was the GS flag was going on and off, so I decided to do a localizer to runway 17L instead of the ILS. Also, the ADF needle swing to the from position so I thought I had crossed the station (leroi) inbound. I know now not to use just one source of information to identify the final approach fix. I know that stations of low power do not always give the most accurate indications. So the best thing to do in that situation would be to wait for the GS to come in and the oral and visual indications of the marker beacon, then use the swing of the needle on the ADF to confirm passage of the station.

Original NASA ASRS Text

Title: SMA ON LOC APCH BEGINS DSCNT TO MDA PRIOR TO PASSAGE OF FINAL APCH FIX.

Narrative: I WAS INBOUND ON THE ILS 17L, OUTSIDE THE OM (LEROI). THE PROB CAME ABOUT WHEN THE ADF NEEDLE SWING TO THE FROM INDICATION. THE PROB WAS DISCOVERED WHEN I WAS DSNDING TO THE MDA OF 860 MSL, WHEN I WAS AT ABOUT 1400 MSL. I IMMEDIATELY STARTED A CLB BACK TO 2300 MSL. THE CONTRIBUTING FACTORS TO THIS WERE IMPROPER XCHK OF LEROI USING THE 055 RADIAL OF WACO VOR, ALSO NOT RECEIVING AN ORAL OR MARKER BEACON LIGHT OR WAITING FOR THE GS TO COME IN. THE REASON I LEFT THE ALT OF 2300 MSL WAS THE GS FLAG WAS GOING ON AND OFF, SO I DECIDED TO DO A LOC TO RWY 17L INSTEAD OF THE ILS. ALSO, THE ADF NEEDLE SWING TO THE FROM POS SO I THOUGHT I HAD CROSSED THE STATION (LEROI) INBOUND. I KNOW NOW NOT TO USE JUST ONE SOURCE OF INFO TO IDENT THE FINAL APCH FIX. I KNOW THAT STATIONS OF LOW PWR DO NOT ALWAYS GIVE THE MOST ACCURATE INDICATIONS. SO THE BEST THING TO DO IN THAT SIT WOULD BE TO WAIT FOR THE GS TO COME IN AND THE ORAL AND VISUAL INDICATIONS OF THE MARKER BEACON, THEN USE THE SWING OF THE NEEDLE ON THE ADF TO CONFIRM PASSAGE OF THE STATION.

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.