What does a radar altimeter measure?

What does a radar altimeter measure?

• A. Altitude above sea level
• B. Altitude above ground
• C. Airspeed
• D. Vertical speed

Answer: (B)

The main idea tested is what a radar instrument actually measures when it gives height information. A radar altimeter determines the distance from the aircraft to the ground directly below it, providing altitude above ground level (AGL). It works by emitting a microwave pulse and timing how long it takes for the reflection to return, then converting that time into a height above the surface. This reading changes with the terrain beneath you, which is why it’s particularly useful at low altitudes during approaches and landings to ensure obstacle clearance. It doesn’t measure altitude above mean sea level, which is derived from barometric pressure readings and is a different kind of height reference. It also doesn’t measure airspeed or vertical speed—the airspeed indicator uses pitot pressure, and the vertical speed indicator shows rate of climb or descent from altitude changes over time.

The main idea tested is what a radar instrument actually measures when it gives height information. A radar altimeter determines the distance from the aircraft to the ground directly below it, providing altitude above ground level (AGL). It works by emitting a microwave pulse and timing how long it takes for the reflection to return, then converting that time into a height above the surface. This reading changes with the terrain beneath you, which is why it’s particularly useful at low altitudes during approaches and landings to ensure obstacle clearance.

It doesn’t measure altitude above mean sea level, which is derived from barometric pressure readings and is a different kind of height reference. It also doesn’t measure airspeed or vertical speed—the airspeed indicator uses pitot pressure, and the vertical speed indicator shows rate of climb or descent from altitude changes over time.