On localizer DME approach, pilot gets reverse sensing on localizer frequency.

Attributes
ACN	170839
Time
Date	199102
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mry
State Reference	CA
Altitude	msl bound lower : 6000 msl bound upper : 6000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : mry
Operator	general aviation : instructional
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 12 flight time total : 500 flight time type : 4
ASRS Report	170839
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

Upon localizer/DME approach to runway 28L at monterey, ca, in an small aircraft, I observed an unusual and unexpected instrument indication. The localizer (110.7) and NDB (385) were in conflict. From my position 6000' about 15 mi northeast of the airport, the localizer was showing the centerline to the right or further north, while the NDB was showing munso left or south, where I believed the airport to be. Closer in I made a visibility sighting of airport environs and indeed it was to the left. After landing I talked to tower personnel who stated that this is a continuing problem unless pilots are aware that the same localizer/ILS frequency 110.7 when used for ILS runway 10R had a morse identifier (i-mry) and when switched for localizer/DME runway 28L then the identifier (i-mts) becomes available. Aside from the identifiers, the frequency is the same, an approaching pilot would have no indication that the localizer 28L would be reversed sensing unless he either checked the identifier or verified direction with the tower. It seems to me that different frequencys or an indication of back course (back course) would solve this problem of reverse sensing west/O notification. Callback conversation with reporter revealed the following information. Reporter states as soon as he had airport in sight, he was cleared for visibility. Had he been actual it would have been a major problem. Tower indicated they changed code depending on runway in use for IFR approach. Reporter concerned because the first two letters of each identifier are the same and in actual an IFR pilot unaware of same frequency but different identification might believe those first two letters and not listen for complete code. Reporter is a ham operator and recognized third letter as incorrect. Called on land line and tower controller confirmed there is a problem. Analyst contacted mry tower and confirmed that approach in use is on the ATIS, but occasionally controller may not FLIP the toggle switch to change direction. He also stated there are many complaints regarding the situation, especially from air carrier pilots.

Original NASA ASRS Text

Title: ON LOC DME APCH, PLT GETS REVERSE SENSING ON LOC FREQ.

Narrative: UPON LOC/DME APCH TO RWY 28L AT MONTEREY, CA, IN AN SMA, I OBSERVED AN UNUSUAL AND UNEXPECTED INSTRUMENT INDICATION. THE LOC (110.7) AND NDB (385) WERE IN CONFLICT. FROM MY POS 6000' ABOUT 15 MI NE OF THE ARPT, THE LOC WAS SHOWING THE CTRLINE TO THE R OR FURTHER N, WHILE THE NDB WAS SHOWING MUNSO L OR S, WHERE I BELIEVED THE ARPT TO BE. CLOSER IN I MADE A VIS SIGHTING OF ARPT ENVIRONS AND INDEED IT WAS TO THE L. AFTER LNDG I TALKED TO TWR PERSONNEL WHO STATED THAT THIS IS A CONTINUING PROB UNLESS PLTS ARE AWARE THAT THE SAME LOC/ILS FREQ 110.7 WHEN USED FOR ILS RWY 10R HAD A MORSE IDENTIFIER (I-MRY) AND WHEN SWITCHED FOR LOC/DME RWY 28L THEN THE IDENTIFIER (I-MTS) BECOMES AVAILABLE. ASIDE FROM THE IDENTIFIERS, THE FREQ IS THE SAME, AN APCHING PLT WOULD HAVE NO INDICATION THAT THE LOC 28L WOULD BE REVERSED SENSING UNLESS HE EITHER CHKED THE IDENTIFIER OR VERIFIED DIRECTION WITH THE TWR. IT SEEMS TO ME THAT DIFFERENT FREQS OR AN INDICATION OF BC (BACK COURSE) WOULD SOLVE THIS PROB OF REVERSE SENSING W/O NOTIFICATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. RPTR STATES AS SOON AS HE HAD ARPT IN SIGHT, HE WAS CLRED FOR VIS. HAD HE BEEN ACTUAL IT WOULD HAVE BEEN A MAJOR PROB. TWR INDICATED THEY CHANGED CODE DEPENDING ON RWY IN USE FOR IFR APCH. RPTR CONCERNED BECAUSE THE FIRST TWO LETTERS OF EACH IDENTIFIER ARE THE SAME AND IN ACTUAL AN IFR PLT UNAWARE OF SAME FREQ BUT DIFFERENT ID MIGHT BELIEVE THOSE FIRST TWO LETTERS AND NOT LISTEN FOR COMPLETE CODE. RPTR IS A HAM OPERATOR AND RECOGNIZED THIRD LETTER AS INCORRECT. CALLED ON LAND LINE AND TWR CTLR CONFIRMED THERE IS A PROB. ANALYST CONTACTED MRY TWR AND CONFIRMED THAT APCH IN USE IS ON THE ATIS, BUT OCCASIONALLY CTLR MAY NOT FLIP THE TOGGLE SWITCH TO CHANGE DIRECTION. HE ALSO STATED THERE ARE MANY COMPLAINTS REGARDING THE SITUATION, ESPECIALLY FROM ACR PLTS.

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.