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Speed of radio wave propagation

Aviation Mechanic Airframe (AMA) practice question 12 of 26 on Communications, Light Signals, and Runway Lighting Systems. ACS element AM.II.I.K1 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONRadio waves radiated from an aircraft antenna propagate out into space at approximately what speed?

  1. A1,100 feet per second
  2. B186,000 miles per second
  3. C300 million miles per second
Show the answer and explanation

Correct answer: B. 186,000 miles per second

  • A — incorrect That figure is roughly the speed of sound in air, not the speed at which a radio wave travels.
  • B — correct The handbook states that radio waves are directional and propagate out into space at 186,000 miles per second.
  • C — incorrect The 300 million figure the handbook uses is in meters per second, not miles per second.

BACKGROUND

A radio wave is an electromagnetic wave produced when alternating current is applied to the center of an antenna. As the current builds and collapses, electric and electromagnetic fields build and collapse around the conductor, and each new cycle forces the not-totally-collapsed fields out into space as radio waves. These waves travel at 186,000 miles per second, and how far they travel depends on the frequency and on the amplification of the signal sent to the antenna. The electric field component and the electromagnetic field component are oriented at 90 degrees to each other and at 90 degrees to the direction of travel.

STUDY TIP

Memorize 186,000 miles per second as the speed of a radio wave, and keep it separate from the 300 million meters per second value the handbook uses when deriving antenna length.

KEY POINTS

  • Radio waves propagate at 186,000 miles per second.
  • Distance traveled depends on frequency and on signal amplification.
  • The electric and electromagnetic field components are 90 degrees apart and 90 degrees to the direction of travel.

SOURCES

  • FAA-H-8083-30B ch11 "Radio Waves"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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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.