Narrative:

We were at 2000 ft MSL on a heading cleared to maintain 2000 ft till established and cleared for the ILS runway 13 at jax. The localizer came alive and the first officer who was flying began a descent to 1700 ft which was the gia. Just after beginning the descent, the localizer began to ping from side to side on both captain and first officer's instruments. We informed jax approach of the problem, climbed back to 2000 ft and were given another vector as we had gone through the course. There were no flags and the identify was good. Approach then said if we continued to have a problem with the ILS, we would be given a surveillance to runway 7. I asked if anyone was in the clear zone and was informed that there was not. Additionally, the aircraft preceding us and behind us had no localizer problems. We continued to have difficulty with the localizer and ended up flying the surveillance to runway 7. The ILS seemed to operate fine on the ground and since we had no problems with it earlier, I thought perhaps someone had used some electronic equipment in the cabin during our approach. I checked with the flight attendants and, in fact, a guy had operated a palm pilot of some sort during the approach. We were unable to talk to the passenger because he had already left the aircraft by the time we talked to the flight attendants. I assumed that was the problem and advised the crew who took the aircraft at jax what had occurred. I did not write up the occurrence in the logbook. After further reflection, I probably should have because there is no way I can prove the palm pilot was the cause.

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Original NASA ASRS Text

Title: B737-300 CREW HAD ERRATIC LOC SIGNALS ON ILS RWY 13 AND RWY 7 AT JAX. A PAX WAS USING A 'PALM PILOT' AT THE TIME.

Narrative: WE WERE AT 2000 FT MSL ON A HDG CLRED TO MAINTAIN 2000 FT TILL ESTABLISHED AND CLRED FOR THE ILS RWY 13 AT JAX. THE LOC CAME ALIVE AND THE FO WHO WAS FLYING BEGAN A DSCNT TO 1700 FT WHICH WAS THE GIA. JUST AFTER BEGINNING THE DSCNT, THE LOC BEGAN TO PING FROM SIDE TO SIDE ON BOTH CAPT AND FO'S INSTS. WE INFORMED JAX APCH OF THE PROB, CLBED BACK TO 2000 FT AND WERE GIVEN ANOTHER VECTOR AS WE HAD GONE THROUGH THE COURSE. THERE WERE NO FLAGS AND THE IDENT WAS GOOD. APCH THEN SAID IF WE CONTINUED TO HAVE A PROB WITH THE ILS, WE WOULD BE GIVEN A SURVEILLANCE TO RWY 7. I ASKED IF ANYONE WAS IN THE CLR ZONE AND WAS INFORMED THAT THERE WAS NOT. ADDITIONALLY, THE ACFT PRECEDING US AND BEHIND US HAD NO LOC PROBS. WE CONTINUED TO HAVE DIFFICULTY WITH THE LOC AND ENDED UP FLYING THE SURVEILLANCE TO RWY 7. THE ILS SEEMED TO OPERATE FINE ON THE GND AND SINCE WE HAD NO PROBS WITH IT EARLIER, I THOUGHT PERHAPS SOMEONE HAD USED SOME ELECTRONIC EQUIP IN THE CABIN DURING OUR APCH. I CHKED WITH THE FLT ATTENDANTS AND, IN FACT, A GUY HAD OPERATED A PALM PILOT OF SOME SORT DURING THE APCH. WE WERE UNABLE TO TALK TO THE PAX BECAUSE HE HAD ALREADY LEFT THE ACFT BY THE TIME WE TALKED TO THE FLT ATTENDANTS. I ASSUMED THAT WAS THE PROB AND ADVISED THE CREW WHO TOOK THE ACFT AT JAX WHAT HAD OCCURRED. I DID NOT WRITE UP THE OCCURRENCE IN THE LOGBOOK. AFTER FURTHER REFLECTION, I PROBABLY SHOULD HAVE BECAUSE THERE IS NO WAY I CAN PROVE THE PALM PILOT WAS THE CAUSE.

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.