MD-80 Series (DC-9-80) Undifferentiated or Other Model
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Passenger Electronic Device; Inflight Event / Encounter Other / Unknown
General None Reported / Taken
Aircraft; Human Factors
While conducting an approach to Runway 5L at RDU we experienced several intermittent full scale localizer fluctuations and a slight map shift as well. These fluctuations began to occur at around 4;000 feet msl.  The weather was VFR and I asked the Tower if they had received any reports of problems with the localizer. They said no (from both aircraft preceding and following us) and that the ILS critical area was clear. The localizer fluctuations ended at about the marker. While we were landing in visual conditions; this would have required a missed approach in IFR weather. After arrival at the gate I asked the flight attendants if they noticed passengers using cell phones and other electronic devices.  They indicated many were. I believe that it is possible many passengers are not leaving their PED's in airplane mode and this could contribute to the signal interruptions we were getting. A review of the aircraft maintenance log the following day showed no faults and ok for service. Now that regulations have changed with regard to portable electronic devices; I believe we are going to see an increase in these type events. I think in addition to flight attendant announcements regarding our policy it would not hurt to have some random sampling of passenger's  devices that are observed in use. They could ask to see the settings page to insure they are in airplane mode.
Air Carrier Captain experiences localizer oscillations during approach in VMC that he suspects may have been caused by an electronic device.