Light Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Workload; Confusion
ATC Issue All Types; Inflight Event / Encounter Unstabilized Approach
Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification
ATC Equipment / Nav Facility / Buildings; Aircraft; Weather
When on the approach (ILS 21) at 3;000 feet out side of CHAMB we were given vectors to join the localizer and cleared for the approach. We were then instructed to contact Tower. As we attempted to join the localizer we both noticed green needle deviation to the right then full deflection. We both agreed to go missed approach and I contacted Tower and informed them that we were going missed approach. Tower asked us to repeat and I did. We immediately executed the published missed approach instructions from the approach plate. Shortly thereafter Tower said they would give us a heading which they did. The published missed altitude was 4;000 FT which [we] proceeded to climb to. Tower instructed us to contact Atlanta Approach and we did. Approach asked what altitude we had been given and we responded the published 4;000 feet. They instructed [us] back down to 3;000 feet and asked our intentions. We said we needed vectors for another ILS approach. We tried a second attempt and found the same NAV deviation. We then asked for the RNAV (GPS) Y Runway 21L. We executed that approach successfully and landed with no problems. After aircraft shut down on the ramp I contacted the Tower to ask if there had been any other reported issues of the ILS 21L. They said in the past there had been but not two in a row.
The reporter believes that an obstruction exists in the vicinity of the localizer antenna causing an unreliable signal. He and other pilots have commented about this anomaly previously; and obviously PDK ATC knows about the potential for the anomaly to affect inbound aircraft. The ILS glideslope issue is documented on the approach plate; the localizer issue should also be noted. He does not remember a NOTAM about the localizer reliability.
We were given vectors and cleared for the ILS Runway 21L approach into PDK. Clearance was maintain 3;000 feet until established on course. Frequency of 111.1 was set in both sides. Inbound course was set at 206 degrees. APPROACH mode was selected. I had previously briefed the pilot not flying that I would hand fly the approach starting at 2;000 feet. We were instructed to contact Tower on frequency 120.9.As we were intercepting the course near CHAMB we noticed the course was never quite captured and the green course indicator kept deviating further to the right until it was out of parameters. With 4;000 feet already set as the missed approach altitude; we initiated a missed approach.The next aircraft successfully accomplished an ILS approach but Tower said it was not unusual for the ILS localizer to be temporarily not working.
A flight crew executed two missed approaches to PDK Runway 21L because of a localizer discrepancy which ATC said occurs occasionally.  No warnings were given to the crew who ultimately landed off the RNAV GPS Y Runway 21L approach.