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Radio selection for transoceanic voice communication

Aviation Mechanic Airframe (AMA) practice question 14 of 26 on Communications, Light Signals, and Runway Lighting Systems. ACS element AM.II.I.K5 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft is being equipped for transoceanic flights that require voice contact far beyond line of sight. Which type of communication radio meets that need?

  1. AA very high frequency (VHF) radio
  2. BAn ultra high frequency (UHF) radio
  3. CA high frequency (HF) radio
Show the answer and explanation

Correct answer: C. A high frequency (HF) radio

  • A — incorrect VHF is the primary aviation communication band, but it travels as space waves that are limited to line of sight.
  • B — incorrect UHF also propagates as a space wave and does not refract off the ionosphere, so it cannot reach beyond line of sight.
  • C — correct HF radio waves refract off the ionosphere as sky waves, which extends their range beyond line of sight, so transoceanic aircraft often use HF for voice communication.

BACKGROUND

Radio waves of different frequencies behave differently in the atmosphere. Very low, low, and medium frequency waves follow the curvature of the earth as ground waves. High frequency waves travel in a straight line but bounce off the ionosphere, and that refraction extends their range well beyond line of sight, which is why the handbook notes that transoceanic aircraft often use HF radios for voice communication in the 2 to 25 MHz range. Everything above HF, including VHF, UHF, and SHF, propagates as space waves that are capable only of line-of-sight transmission.

STUDY TIP

Tie each frequency band to its propagation mode: ground wave, sky wave, or space wave. The sky wave behavior of HF is the single fact that explains long-range oceanic voice work.

KEY POINTS

  • HF waves refract off the ionosphere and reach beyond line of sight.
  • Transoceanic aircraft use HF voice radios in the 2 to 25 MHz range.
  • VHF and UHF are space waves limited to line of sight.

SOURCES

  • FAA-H-8083-30B ch11 "Types of Radio Waves"
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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.