Narrative:

330 degree heading to intercept localizer runway 1R. Captain navigation radio tuned to localizer, first officer tuned to aml for DME. Attempting to obtain valid identify for iad but signal was very weak. Finally began receiving a very weak, but correct, identify with warning flags intermittently going out of view. Tille NDB was not being received at the time and was not available as a backup. We were just about to query approach regarding status of runway 1R localizer when approach called us to inform us that we did not intercept the localizer and we were now crossing the runway 1L final. I immediately turned back to the right to re-establish an intercept heading to the runway 1R final and at that time was able to visually acquire the iad airport. Runway 1L was being used for departures so there was no conflict. One aircraft following us was told to intentionally overshoot the runway 1R localizer to maintain spacing behind us while we corrected our course. During our course correction to runway 1R, the first officer's navigation radio was selected to the localizer (versus aml) and we started receiving course guidance. My localizer came alive at just about the same time, as did the tille NDB. Approach and landing was uneventful from this point. The cause of this problem, from our point of view, was a weak signal at the distance and altitude we were flying. I'm not sure exactly the distance the signal became usable since no DME was available, but I'm guessing about 20 DME. Our next leg was iad-mco, and both navigation receivers worked normally with stray localizer (runway 17) signals received and idented outside 30 NM.

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Original NASA ASRS Text

Title: B737 CREW OVERSHOT THE LOC COURSE.

Narrative: 330 DEG HDG TO INTERCEPT LOC RWY 1R. CAPT NAV RADIO TUNED TO LOC, FO TUNED TO AML FOR DME. ATTEMPTING TO OBTAIN VALID IDENT FOR IAD BUT SIGNAL WAS VERY WEAK. FINALLY BEGAN RECEIVING A VERY WEAK, BUT CORRECT, IDENT WITH WARNING FLAGS INTERMITTENTLY GOING OUT OF VIEW. TILLE NDB WAS NOT BEING RECEIVED AT THE TIME AND WAS NOT AVAILABLE AS A BACKUP. WE WERE JUST ABOUT TO QUERY APCH REGARDING STATUS OF RWY 1R LOC WHEN APCH CALLED US TO INFORM US THAT WE DID NOT INTERCEPT THE LOC AND WE WERE NOW XING THE RWY 1L FINAL. I IMMEDIATELY TURNED BACK TO THE R TO RE-ESTABLISH AN INTERCEPT HDG TO THE RWY 1R FINAL AND AT THAT TIME WAS ABLE TO VISUALLY ACQUIRE THE IAD ARPT. RWY 1L WAS BEING USED FOR DEPS SO THERE WAS NO CONFLICT. ONE ACFT FOLLOWING US WAS TOLD TO INTENTIONALLY OVERSHOOT THE RWY 1R LOC TO MAINTAIN SPACING BEHIND US WHILE WE CORRECTED OUR COURSE. DURING OUR COURSE CORRECTION TO RWY 1R, THE FO'S NAV RADIO WAS SELECTED TO THE LOC (VERSUS AML) AND WE STARTED RECEIVING COURSE GUIDANCE. MY LOC CAME ALIVE AT JUST ABOUT THE SAME TIME, AS DID THE TILLE NDB. APCH AND LNDG WAS UNEVENTFUL FROM THIS POINT. THE CAUSE OF THIS PROB, FROM OUR POINT OF VIEW, WAS A WEAK SIGNAL AT THE DISTANCE AND ALT WE WERE FLYING. I'M NOT SURE EXACTLY THE DISTANCE THE SIGNAL BECAME USABLE SINCE NO DME WAS AVAILABLE, BUT I'M GUESSING ABOUT 20 DME. OUR NEXT LEG WAS IAD-MCO, AND BOTH NAV RECEIVERS WORKED NORMALLY WITH STRAY LOC (RWY 17) SIGNALS RECEIVED AND IDENTED OUTSIDE 30 NM.

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.