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If during an ILS approach after having been established the pilot deviates by more than half scale deflection on the Localizer:
  • A
    an immediate missed approach should be executed because obstacle clearance may no longer be guaranteed.
  • B
    the approach may be completed as long as the associated locator gives the information that the aircraft is on the centre line.
  • C
    the approach may be continued but a warning for excessive beam bends should be generated.
  • D
    the approach may be continued as long as the GP needle has less than a half scale deflection.

The Instrument Landing System (ILS) is a system that provides the guidance of an aircraft towards the final approach. The system provides the aircraft with specific horizontal (localizer) and vertical (glideslope) guidance. With determining the limits of these guidances there will be a specific area determined which is clear of obstacles.

An aircraft that has turned onto the inbound heading and is within 2,5 degrees of the localizer course (which means half a scale of deflection on the ILS instrument in the cockpit) is established on the final approach course.

Half a scale of deflection are the boundaries of the ILS and once going further than half a scale deflection, there might not be enough obstacle clearance and a go around should be initiated.

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