During radar altimeter testing, what is the purpose of range and ground reference checks?

During radar altimeter testing, what is the purpose of range and ground reference checks?

• A. To verify that altitude readings correspond to a known elevation reference
• B. To align the antenna to the magnetic north
• C. To calibrate the weather radar
• D. To test the cockpit mic

Answer: (A)

Radar altimeters measure height above the ground by sending a radar pulse and timing its return. Range checks verify that the system accurately reports distances to surfaces at known separations, proving the instrument reads the ground distance correctly across the test range. Ground reference checks ensure the altitude reading corresponds to a defined elevation reference—often the actual ground elevation at the test site—while also accounting for the physical height of the antenna above that reference plane. Together, these checks confirm that altitude indications map to a known, real elevation, which is essential for safe operation during low-altitude flight and approaches. The other tasks mentioned—aligning an antenna to magnetic north, calibrating weather radar, or testing a cockpit microphone—address different systems and do not relate to the radar altimeter’s height measurement against a ground reference.

Radar altimeters measure height above the ground by sending a radar pulse and timing its return. Range checks verify that the system accurately reports distances to surfaces at known separations, proving the instrument reads the ground distance correctly across the test range. Ground reference checks ensure the altitude reading corresponds to a defined elevation reference—often the actual ground elevation at the test site—while also accounting for the physical height of the antenna above that reference plane. Together, these checks confirm that altitude indications map to a known, real elevation, which is essential for safe operation during low-altitude flight and approaches. The other tasks mentioned—aligning an antenna to magnetic north, calibrating weather radar, or testing a cockpit microphone—address different systems and do not relate to the radar altimeter’s height measurement against a ground reference.