ACR MLG OBSERVED OFF COURSE BY ATC CTLR DURING DEP. SUSPECT PAX USE OF PERSONAL ELECTRONIC DEVISE.

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CAPT WAS FLYING ACFT OUTBOUND ON THE PALEO 2 DEP FROM BWI. CAPT WAS TRACKING THE 276 DEGS RADIAL TO SIE AND COCKPIT DISPLAY SHOWED ON COURSE. MY NAV RECEIVER WAS TUNED TO ENO VOR FOR THE NEXT LEG OF THE SID. BALTIMORE DEP ASKED US TO TURN 30 DEGS L TO RE-INTERCEPT THE SID. CAPT'S INDICATOR SHOWED HIM EXACTLY ON COURSE. I FLIPPED MY VOR RECEIVER BACK TO SIE AND MY NEEDLE CTRED WITH 276 DEG RADIAL DIALED IN. WE MENTIONED TO ATC THAT WE SHOW ON COURSE. ATC SAID THAT WE WERE 10 MI S OF COURSE. WE TURNED TO THE ASSIGNED HDG AND ATC TOLD US TO INTERCEPT THE PXT 046 DEG RADIAL FOR THE WARRD 4 STAR INTO EWR. WE TUNED IN PXT AND BOTH NAV UNITS DISPLAYED IDENTICAL BEARINGS. SOON THE NEEDLES CTRED AND CAPT TURNED THE AIRPLANE TO TRACK THE 046 DEGS PXT RADIAL. FEW MINS LATER; CTR TOLD US WE WERE OFF COURSE AND GAVE US A HDG TOWARD RBV. I THOUGHT OF THE POSSIBILITY OF PORTABLE ELECTRONIC DEVICE INTERFERENCE FROM A PAX IN THE CABIN. I ASKED THE CAPT IF HE FELT THIS WAS A POSSIBILITY AND SHOULD I CALL ONE OF THE FLT ATTENDANTS TO ASK IF ANYONE IS USING A PED. CAPT APPROVED THE INVESTIGATION. THE LEAD FLT ATTENDANT RPTED THE ONLY PAX USING A PED WAS IN FIRST CLASS SEAT 2C USING A LAP-TOP PORTABLE COMPUTER (COMPANY MANUFACTURER). WE ASKED THE LEAD IF SHE WOULD KINDLY ASK THE PAX TO TURN THE UNIT OFF FOR REMAINDER OF FLT. HE KINDLY DID AND WE DID NOT HAVE ANY FURTHER NAV DIFFICULTIES. I COMPLETED A PED INTERFERENCE RPT AND MAILED IT TO SAFETY ORGANIZATION.