Narrative:

On the approach into bwi, the first officer was flying and I was required to keep my VOR on the balance frequency to monitor DME for the approach until the final approach fix. The autoplt had captured the localizer and I made the callout 'localizer captured' and advised the first officer that he was free to go ahead and descend on the glide slope. As I looked at the approach progress display to verify that the glide slope was captured, something did not look right. The annunciator said that the glide slope was captured, but not the localizer. After a couple of double takes looking at the display, I looked over at the first officer's VOR, and sure enough, the CDI was off-scale and pegged to the left. I called out full scale deflection just as we broke out of the clouds and found that we were about 1 mi to the right of centerline. The first officer had not noticed anything unusual until I made the callout. Both pilots were alert and focused and flying by the book. In retrospect, I believe that the aircraft instruments had been affected by cell phones or other equipment in the aircraft cabin. I may have inadvertently attributed to this by making an announcement as we started our descent about the war in iraq. ATC had made a broadcast in the blind that the liberation of iraq had just begun. The tension created by imminent war was on everyone's mind and I was happy to share the news with the people in the cabin. However, the events during the past 2 yrs have shown that cell phones proliferate and can be used from the back of an airplane. I have no other logical explanation for the autoplt being locked onto a localizer 1 min and 1 mi off course the next moment. Several other factors could have made this event much worse: 1) the ATIS was calling the WX few clouds at around 2000 ft (I can't remember exactly) and a ceiling of 4700 ft. The actual ceiling on final was about 1800 ft. This happens a lot and seems to happen much more often at the fields that use automated ATIS. 2) no warning was ever issued by approach control. We were being handed off to the tower at the time and the tower didn't mention our being off course either. 3) the fact that the approach requires 1 NAVAID to be set to the VOR-DME meant that 1 pilot was not presented with a localizer to monitor. This is less than optimum especially for a CAT 3 runway. In the past (on 1 occasion) I have actually seen a cell phone cause a localizer needle to be centered with no off flag when the airplane was not on the course during VMC. Suggestions for prevention: never make a PA that might encourage the use of a cell phone during flight.

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Original NASA ASRS Text

Title: AN ACR B737-700 CREW, ON APCH TO BWI RWY 10, ATTRIBUTES BEING OFF COURSE TO POSSIBLE UNAUTH USE OF CELL PHONES PROMPTED BY A CABIN ANNOUNCEMENT. THE INABILITY OF THE CREW TO BOTH BE ON THE ILS FREQ BECAUSE OF THE APCH DESIGN, ALSO MAYBE A CONTRIBUTING FACTOR.

Narrative: ON THE APCH INTO BWI, THE FO WAS FLYING AND I WAS REQUIRED TO KEEP MY VOR ON THE BAL FREQ TO MONITOR DME FOR THE APCH UNTIL THE FINAL APCH FIX. THE AUTOPLT HAD CAPTURED THE LOC AND I MADE THE CALLOUT 'LOC CAPTURED' AND ADVISED THE FO THAT HE WAS FREE TO GO AHEAD AND DSND ON THE GLIDE SLOPE. AS I LOOKED AT THE APCH PROGRESS DISPLAY TO VERIFY THAT THE GLIDE SLOPE WAS CAPTURED, SOMETHING DID NOT LOOK RIGHT. THE ANNUNCIATOR SAID THAT THE GLIDE SLOPE WAS CAPTURED, BUT NOT THE LOC. AFTER A COUPLE OF DOUBLE TAKES LOOKING AT THE DISPLAY, I LOOKED OVER AT THE FO'S VOR, AND SURE ENOUGH, THE CDI WAS OFF-SCALE AND PEGGED TO THE L. I CALLED OUT FULL SCALE DEFLECTION JUST AS WE BROKE OUT OF THE CLOUDS AND FOUND THAT WE WERE ABOUT 1 MI TO THE R OF CTRLINE. THE FO HAD NOT NOTICED ANYTHING UNUSUAL UNTIL I MADE THE CALLOUT. BOTH PLTS WERE ALERT AND FOCUSED AND FLYING BY THE BOOK. IN RETROSPECT, I BELIEVE THAT THE ACFT INSTS HAD BEEN AFFECTED BY CELL PHONES OR OTHER EQUIP IN THE ACFT CABIN. I MAY HAVE INADVERTENTLY ATTRIBUTED TO THIS BY MAKING AN ANNOUNCEMENT AS WE STARTED OUR DSCNT ABOUT THE WAR IN IRAQ. ATC HAD MADE A BROADCAST IN THE BLIND THAT THE LIBERATION OF IRAQ HAD JUST BEGUN. THE TENSION CREATED BY IMMINENT WAR WAS ON EVERYONE'S MIND AND I WAS HAPPY TO SHARE THE NEWS WITH THE PEOPLE IN THE CABIN. HOWEVER, THE EVENTS DURING THE PAST 2 YRS HAVE SHOWN THAT CELL PHONES PROLIFERATE AND CAN BE USED FROM THE BACK OF AN AIRPLANE. I HAVE NO OTHER LOGICAL EXPLANATION FOR THE AUTOPLT BEING LOCKED ONTO A LOC 1 MIN AND 1 MI OFF COURSE THE NEXT MOMENT. SEVERAL OTHER FACTORS COULD HAVE MADE THIS EVENT MUCH WORSE: 1) THE ATIS WAS CALLING THE WX FEW CLOUDS AT AROUND 2000 FT (I CAN'T REMEMBER EXACTLY) AND A CEILING OF 4700 FT. THE ACTUAL CEILING ON FINAL WAS ABOUT 1800 FT. THIS HAPPENS A LOT AND SEEMS TO HAPPEN MUCH MORE OFTEN AT THE FIELDS THAT USE AUTOMATED ATIS. 2) NO WARNING WAS EVER ISSUED BY APCH CTL. WE WERE BEING HANDED OFF TO THE TWR AT THE TIME AND THE TWR DIDN'T MENTION OUR BEING OFF COURSE EITHER. 3) THE FACT THAT THE APCH REQUIRES 1 NAVAID TO BE SET TO THE VOR-DME MEANT THAT 1 PLT WAS NOT PRESENTED WITH A LOC TO MONITOR. THIS IS LESS THAN OPTIMUM ESPECIALLY FOR A CAT 3 RWY. IN THE PAST (ON 1 OCCASION) I HAVE ACTUALLY SEEN A CELL PHONE CAUSE A LOC NEEDLE TO BE CTRED WITH NO OFF FLAG WHEN THE AIRPLANE WAS NOT ON THE COURSE DURING VMC. SUGGESTIONS FOR PREVENTION: NEVER MAKE A PA THAT MIGHT ENCOURAGE THE USE OF A CELL PHONE DURING FLT.

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.