Narrative:

We were cleared for the ILS 1L at iad. The airport was VMC with a scattered to broken layer between us and the runway. When cleared for the approach, I (the PF) properly armed the navigation equipment on the fcp, while the EFIS showed the localizer and GS captured. We had a full right deflection of the localizer needle. I realized that the situation was not normal. (It should not have shown a full deflection with a localizer 2 captured displayed.) almost simultaneously, the captain, the controller, and I realized that we had flown through the inbound course. The needle made a rapid swing to a full left deflection. I turned off the autoplt and made a left turn at about the same time the controller told us to make a left turn quickly. The runway was now in sight and we landed without further incident. I can only speculate as to what may have caused this situation. On the carj we have the ability to hold DME information from a VOR. While this is an ILS DME approach, I noticed (after arming the fcp) that I was not receiving DME information. I then switched briefly to the VOR and pressed the hold button on the navigation radio and then back to the ILS frequency. My first thought was that I had not switched back to the ILS frequency, but the captain and I both verified that the proper frequency was selected. Perhaps (and once again I speculate) when I switched to hold the VOR DME, the computer locked onto the VOR signal and retained it even after I switched back to the ILS frequency, the entire time showing localizer 2 captured. I will be in a discussion with company personnel about the situation.

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Original NASA ASRS Text

Title: AN ACR FLC FLYING CRJ AT IAD FAILED TO INTERCEPT THE LOC COURSE AS INSTRUCTED BY ATC AND WAS GIVEN ADDITIONAL FLT ASSIST TO THE FINAL APCH COURSE.

Narrative: WE WERE CLRED FOR THE ILS 1L AT IAD. THE ARPT WAS VMC WITH A SCATTERED TO BROKEN LAYER BTWN US AND THE RWY. WHEN CLRED FOR THE APCH, I (THE PF) PROPERLY ARMED THE NAV EQUIP ON THE FCP, WHILE THE EFIS SHOWED THE LOC AND GS CAPTURED. WE HAD A FULL R DEFLECTION OF THE LOC NEEDLE. I REALIZED THAT THE SIT WAS NOT NORMAL. (IT SHOULD NOT HAVE SHOWN A FULL DEFLECTION WITH A LOC 2 CAPTURED DISPLAYED.) ALMOST SIMULTANEOUSLY, THE CAPT, THE CTLR, AND I REALIZED THAT WE HAD FLOWN THROUGH THE INBOUND COURSE. THE NEEDLE MADE A RAPID SWING TO A FULL L DEFLECTION. I TURNED OFF THE AUTOPLT AND MADE A L TURN AT ABOUT THE SAME TIME THE CTLR TOLD US TO MAKE A L TURN QUICKLY. THE RWY WAS NOW IN SIGHT AND WE LANDED WITHOUT FURTHER INCIDENT. I CAN ONLY SPECULATE AS TO WHAT MAY HAVE CAUSED THIS SIT. ON THE CARJ WE HAVE THE ABILITY TO HOLD DME INFO FROM A VOR. WHILE THIS IS AN ILS DME APCH, I NOTICED (AFTER ARMING THE FCP) THAT I WAS NOT RECEIVING DME INFO. I THEN SWITCHED BRIEFLY TO THE VOR AND PRESSED THE HOLD BUTTON ON THE NAV RADIO AND THEN BACK TO THE ILS FREQ. MY FIRST THOUGHT WAS THAT I HAD NOT SWITCHED BACK TO THE ILS FREQ, BUT THE CAPT AND I BOTH VERIFIED THAT THE PROPER FREQ WAS SELECTED. PERHAPS (AND ONCE AGAIN I SPECULATE) WHEN I SWITCHED TO HOLD THE VOR DME, THE COMPUTER LOCKED ONTO THE VOR SIGNAL AND RETAINED IT EVEN AFTER I SWITCHED BACK TO THE ILS FREQ, THE ENTIRE TIME SHOWING LOC 2 CAPTURED. I WILL BE IN A DISCUSSION WITH COMPANY PERSONNEL ABOUT THE SIT.

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.