Narrative:

While being vectored for approach course intercept, both ILS signals were aurally monitored and identified. Flags disappeared from localizer and GS indicators as usual as aircraft got within a few mi of final approach course. The final course was intercepted normally. As the ILS approach was commenced at about 12 NM out, both sets of localizer and GS flags appeared in captain's and first officer's instruments. The approach was discontinued, the cabin crew made an announcement concerning electronic devices. A second attempt at the approach yielded the same result except this time the flags were intermittent. The aural identify each time had interference 'covering' the signal. The cabin crew was dispatched to inspect each row for electronic devices. The only discovery was an aircraft installed 'air phone.' the flight crew requested that approach vector us lower and closer to final in order to receive as strong a signal as possible. The third approach was successful. The captain made a PA before the 3RD attempt to explain the interference problem. No one admitted to using any electronic devices and none were discovered. The ILS receivers were written up to see if they may have been malfunctioning. I doubt it. I suspect EMI from the cabin.

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Original NASA ASRS Text

Title: LOC AND GS FLAGS APPEAR ON CAPT AND FO INSTS DURING APCH. MISSED APCH TWICE.

Narrative: WHILE BEING VECTORED FOR APCH COURSE INTERCEPT, BOTH ILS SIGNALS WERE AURALLY MONITORED AND IDENTIFIED. FLAGS DISAPPEARED FROM LOC AND GS INDICATORS AS USUAL AS ACFT GOT WITHIN A FEW MI OF FINAL APCH COURSE. THE FINAL COURSE WAS INTERCEPTED NORMALLY. AS THE ILS APCH WAS COMMENCED AT ABOUT 12 NM OUT, BOTH SETS OF LOC AND GS FLAGS APPEARED IN CAPT'S AND FO'S INSTS. THE APCH WAS DISCONTINUED, THE CABIN CREW MADE AN ANNOUNCEMENT CONCERNING ELECTRONIC DEVICES. A SECOND ATTEMPT AT THE APCH YIELDED THE SAME RESULT EXCEPT THIS TIME THE FLAGS WERE INTERMITTENT. THE AURAL IDENT EACH TIME HAD INTERFERENCE 'COVERING' THE SIGNAL. THE CABIN CREW WAS DISPATCHED TO INSPECT EACH ROW FOR ELECTRONIC DEVICES. THE ONLY DISCOVERY WAS AN ACFT INSTALLED 'AIR PHONE.' THE FLT CREW REQUESTED THAT APCH VECTOR US LOWER AND CLOSER TO FINAL IN ORDER TO RECEIVE AS STRONG A SIGNAL AS POSSIBLE. THE THIRD APCH WAS SUCCESSFUL. THE CAPT MADE A PA BEFORE THE 3RD ATTEMPT TO EXPLAIN THE INTERFERENCE PROB. NO ONE ADMITTED TO USING ANY ELECTRONIC DEVICES AND NONE WERE DISCOVERED. THE ILS RECEIVERS WERE WRITTEN UP TO SEE IF THEY MAY HAVE BEEN MALFUNCTIONING. I DOUBT IT. I SUSPECT EMI FROM THE CABIN.

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.