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FM broadcast stations transmitting just below 108 MHz are…

  • A
    causing interference only in extreme cases, affecting exclusively the glide path.
  • B
    likely to cause interference to ILS receivers not equipped with an immunity filter.
  • C
    unlikely to cause any interference to ILS receivers.
  • D
    likely to cause interference to all ILS receivers.

The Instrument Landing System (ILS) localizer operates between 108 and 111.975 MHz.
FM broadcasting is a method of radio broadcasting using Frequency Modulation (FM).FM broadcasting uses the same frequency range as the ILS, the Very High Frequency (VHF) range.

The receiving unit of the ILS on the aircraft will receive the radio waves that the ILS is sending out. Apart from the correct radiowaves, the receiving unit can also receive the broadcasted FM radio signals, which will interfere the ILS indication and might give false data. Adding onboard Electro Magnetic Interference (EMI) filters, immunity filters or special layout techniques can help in bypassing the interference received from the FM broadcasts.

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