A Radio Altimeter is an airborne electronic device capable of measuring the height of the aircraft above terrain immediately below the aircraft.
- Also known as Radar Altimeter (RA), Electronic Altimeter, or Reflection Altimeter.
- Measures the distance by timing how long it takes a beam of radio waves to travel to the ground, reflect, and return to the aircraft.
- In most cases, the device is operational up to 2,500 feet above ground level (AGL).
- The operating frequency range is 4250 to 4350 MHz.
Radio altimeter calls may be either:
- Announced by one of the pilots, usually Pilot Flying (PF) and Pilot Monitoring (PM), either in accordance with SOPs or on an ad hoc basis, or
- Generated automatically by a synthetic voice.
Many operators have SOPs which requires a pilot call for “Rad Alt Live” to be made during descent as soon as practicable after height indications reappear at 2500 feet agl, in order to enhance crew awareness of proximity to terrain.
The use of the radio altimeter is integral to both the function of ground proximity warning systems and to the operation of aircraft during Cat 2/3 approaches where it is used to determine the position of the aircraft in relation to the applicable decision height.
Prudent use of the radio altimeter can be a valuable defence against Controlled Flight Into Terrain (CFIT).
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