Originally Posted by
M Invernoz
Yes, I know there´s a lot of info about the critical and sensitive areas of the ILS. But they all refer to the vehicles or aircraft ¨on ground¨, not about several Aircraft on the LOC. I know there are tons of airports like Zurich or Heathrow where they have 4 o 5 planes on final But is there any advisory or information about the interference on LOC signals when this approaches are made? any aircraft in the world performed a go around due to signal lost?
Perhaps you are thinking of the ILS as some pencil-thin guidance beam that the aircraft flies down. In which case you may think that aircraft ahead might "block" the signal. In reality that is not how it works. The Localiser is actually two transmission beams with quite a wide spread. The narrow centre-line guidance is just where the two signals exactly balance. That is a simplification but good enough for here I think. Remember also that the localiser equipment is some way beyond the far end of the runway, so any aircraft ahead may be between you and the runway threshold but are not between you and the localiser antennas.
As said before, the main risk is when an aircraft at the far end of the runway turns off and creates a non-symmetrical distortion of the radio beams (it is now quite close to the antennas) and this potentially shifts the balance point of the two signals as seen by the approaching aircraft.