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The radio altimeter:

1 – operates in the 1600-1660 kHz range
2 – operates in the 4200-4400 MHz range
3 – measures a frequency difference
4 – measures an amplitude difference.

The combination that regroups all of the correct statements is:

  • A
    1, 3.
  • B
    2, 4.
  • C
    1, 4.
  • D
    2, 3.
The radio altimeter can be defined as a self-contained on-board aid used to measure the true height of the aircraft. The RA operates between 4200 MHz and 4400 MHz and the maximum range for indication is typically from the ground up to 2 500 ft. The height measurement is based upon a frequency modulation wave, for which the frequency difference between the transmitted wave and the received wave after ground reflection is measured. It provides data to the TCAS, the GPWS, and the Autoland system.

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