ILS Fluctuations Caused by Movements through ILS-Critical Areas

April 19, 2012 - The FAA has released an Information-for-Operators (InFO) bulletin due to reports from both pilots and air traffic controllers of instances of localizer and/or glideslope fluctuations while the aircraft is navigating on the ILS. This phenomenon may occur when aircraft or vehicles are moving through the ILS-critical areas and is due to interference with the ILS signals.

If flying a coupled approach, the aircraft autoflight system may follow the ILS fluctuations, resulting in unexpected pitch, roll, or autopilot behavior. It is important to realize that ATC does not keep aircraft or vehicles out of the “ILS-critical area” unless the ceiling is below 800’ or the visibility is below 2 miles, so both VMC and some IMC operations may be affected. Read the FAA Bulletin.