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Primary altitude range for radio altimeter use

Aviation Mechanic Airframe (AMA) practice question 21 of 26 on Communications, Light Signals, and Runway Lighting Systems. ACS element AM.II.I.K19 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA radio altimeter is used primarily during instrument approach and low level or night flight in what altitude range?

  1. AAbove 18,000 feet
  2. BBetween 5,000 and 10,000 feet
  3. CBelow 2,500 feet
Show the answer and explanation

Correct answer: C. Below 2,500 feet

  • A — incorrect At that altitude the aircraft is far above the terrain-measuring range the instrument is intended to serve.
  • B — incorrect The stated application is low level flight, not a mid-altitude band.
  • C — correct The handbook states the radio altimeter is used primarily during instrument approach and low level or night flight below 2,500 feet.

BACKGROUND

A radio altimeter uses a transceiver and a directional antenna to broadcast a 4.3 GHz carrier wave, frequency modulated at 50 MHz, straight down toward the ground. The signal strikes surface features and bounces back to a second antenna, and the transceiver computes height above ground level from the elapsed time and the frequency modulation. The handbook states the instrument is used primarily during instrument approach and low level or night flight below 2,500 feet, and it supplies the primary altitude information for landing decision height. An adjustable altitude bug creates a visual or aural warning when the aircraft reaches the selected decision height.

STUDY TIP

Link the radio altimeter to approach and landing work below 2,500 feet, and remember it is the source of decision height information.

KEY POINTS

  • The radio altimeter is used primarily below 2,500 feet.
  • It broadcasts a 4.3 GHz carrier wave and measures height above ground level.
  • It supplies the primary altitude information for landing decision height.

SOURCES

  • FAA-H-8083-31B ch11 "Radio Altimeter"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.