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Refer to figure.
An aircraft is established on the ILS approach shown in the figure, with the marker beacons correctly tuned and functional. The pilot hears continuous Morse code in the following pattern; dot - dash - dot - dash - dot - dash. How far from the runway threshold is the aircraft?

  • A

    5.9

  • B

    5.4

  • C

    1

  • D

    0.5

Refer to figure.
Marker beacons can be installed as part of an Instrument Landing System (ILS). They provide location information to pilots and are noted on approach charts so pilots can confirm their position on the approach. Nowadays they are generally replaced with DME as this has more advantages.

Outer marker (OM): Located between 3 and 6 nm from the runway threshold along the localiser. When passing the outer marker, the pilot receives a low pitch audio tone modulated at 400 Hz in a series of dashes (2 per second) "- - - - - - "  accompanied by a flashing blue light on the instrument panel or PFD.

Middle marker (MM): Located between 0.5 and 1 nm from the runway threshold. When passing the middle marker, the pilot receives a low pitch audio tone modulated at 1300 Hz in a continuous series of dots and dashes "- . - . - . - ." accompanied by a flashing amber light on the instrument panel or PFD.

Inner marker (IM): Located “near” the threshold. When passing the inner marker, the pilot receives a low pitch audio tone modulated at 3000 Hz in a continuous series of dots  ". . . . .  ." accompanied by a flashing white light on the instrument panel or PFD.

This question is therefore asking about the Middle Marker, so we need to look at the figure provided, find the Middle Marker (marked in red) and read off the DME distance to the threshold; 0.5.

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