Small aircraft pilot received false indication of marker beacon started descent too soon.

Attributes
ACN	264452
Time
Date	199402
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : see
State Reference	CA
Altitude	msl bound lower : 2000 msl bound upper : 2000
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Controlling Facilities	tower : see
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi pilot : instrument
Experience	flight time last 90 days : 24 flight time total : 1250 flight time type : 400
ASRS Report	264452
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	altitude deviation : crossing restriction not met non adherence : published procedure non adherence : clearance other spatial deviation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other

Narrative:

While executing the see localizer-D approach, I had passed samos (FAF) and descended to 2400 ft awaiting grigg (a fan marker). Shortly after leveling at 2400 ft I heard the audio identify for grigg and got a white marker beacon flashing light (indicating I was at grigg), whereupon I commenced descent to 1520 ft (MDA). See tower then advised me of a 'low altitude alert' and stated that the minimum altitude in my sector for the approach was 2400 ft. I advised that I was inside grigg and going down to 1520 ft. At that moment I heard a much louder audio identify for grigg and got another white marker beacon light (the previous audio and marker light had lasted only a few seconds). I continued descent to the MDA and, upon time expiration, started to commence a missed approach, when I then broke out and saw the airport. I circled west of runway 17 (after maneuvering to remain clear of clouds) and landed runway 17. Upon return to my home base I had the marker beacons checked and no problem was found. I assume that I received an early or phantom audio and visual (marker light) indication for grigg. My only indication that grigg may not have been crossed was that these (audio/visual marker light) signals lasted only a few seconds, whereas the second time I heard and saw the indications for grigg the audio and visual indications were louder/lasted longer. The localizer-D approach, as well as see airport, are in an area of hills with a few higher peaks to the northeast. Perhaps the terrain had a phantom/premature signal effect on reception of the fan marker (grigg). It was IMC with ragged low ceilings. I would urge a flight check of this approach to determine if such premature or phantom signals are present under the same conditions. Callback conversation with reporter revealed the following information: call to tower reveals that they are not aware of any problems with false passage or have received any other pilot complaints.

Original NASA ASRS Text

Title: SMA PLT RECEIVED FALSE INDICATION OF MARKER BEACON STARTED DSCNT TOO SOON.

Narrative: WHILE EXECUTING THE SEE LOC-D APCH, I HAD PASSED SAMOS (FAF) AND DSNDED TO 2400 FT AWAITING GRIGG (A FAN MARKER). SHORTLY AFTER LEVELING AT 2400 FT I HEARD THE AUDIO IDENT FOR GRIGG AND GOT A WHITE MARKER BEACON FLASHING LIGHT (INDICATING I WAS AT GRIGG), WHEREUPON I COMMENCED DSCNT TO 1520 FT (MDA). SEE TWR THEN ADVISED ME OF A 'LOW ALT ALERT' AND STATED THAT THE MINIMUM ALT IN MY SECTOR FOR THE APCH WAS 2400 FT. I ADVISED THAT I WAS INSIDE GRIGG AND GOING DOWN TO 1520 FT. AT THAT MOMENT I HEARD A MUCH LOUDER AUDIO IDENT FOR GRIGG AND GOT ANOTHER WHITE MARKER BEACON LIGHT (THE PREVIOUS AUDIO AND MARKER LIGHT HAD LASTED ONLY A FEW SECONDS). I CONTINUED DSCNT TO THE MDA AND, UPON TIME EXPIRATION, STARTED TO COMMENCE A MISSED APCH, WHEN I THEN BROKE OUT AND SAW THE ARPT. I CIRCLED W OF RWY 17 (AFTER MANEUVERING TO REMAIN CLR OF CLOUDS) AND LANDED RWY 17. UPON RETURN TO MY HOME BASE I HAD THE MARKER BEACONS CHKED AND NO PROB WAS FOUND. I ASSUME THAT I RECEIVED AN EARLY OR PHANTOM AUDIO AND VISUAL (MARKER LIGHT) INDICATION FOR GRIGG. MY ONLY INDICATION THAT GRIGG MAY NOT HAVE BEEN CROSSED WAS THAT THESE (AUDIO/VISUAL MARKER LIGHT) SIGNALS LASTED ONLY A FEW SECONDS, WHEREAS THE SECOND TIME I HEARD AND SAW THE INDICATIONS FOR GRIGG THE AUDIO AND VISUAL INDICATIONS WERE LOUDER/LASTED LONGER. THE LOC-D APCH, AS WELL AS SEE ARPT, ARE IN AN AREA OF HILLS WITH A FEW HIGHER PEAKS TO THE NE. PERHAPS THE TERRAIN HAD A PHANTOM/PREMATURE SIGNAL EFFECT ON RECEPTION OF THE FAN MARKER (GRIGG). IT WAS IMC WITH RAGGED LOW CEILINGS. I WOULD URGE A FLT CHK OF THIS APCH TO DETERMINE IF SUCH PREMATURE OR PHANTOM SIGNALS ARE PRESENT UNDER THE SAME CONDITIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALL TO TWR REVEALS THAT THEY ARE NOT AWARE OF ANY PROBS WITH FALSE PASSAGE OR HAVE RECEIVED ANY OTHER PLT COMPLAINTS.

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.