When visibility is low, cloudy, dark, or you are flying over open waters at night, it is very difficult and sometimes impossible to see the horizon or to know where you are in the sky. Without instruments, the pilot is essentially flying blindly through the sky. In this environment, the aircraft can quickly find itself much closer to the earth than the pilot might have calculated.

Speed is life, altitude is life insurance. No one has ever collided with the sky.

What Is an Altimeter

apn-232 combined altitude radar altimeter cara

Also read: Terrain, Terrain, Pull Up! Pull Up!

An altimeter is an instrument that measures the altitude, or height, of an object in relation to what is under it. When it comes to altitude measurement in aviation, there are two different instruments in an airplane or helicopter. Those are a barometric altimeter and a radar altimeter.

What Is a Barometric Altimeter

Using atmospheric pressure, the barometric altimeter measures the height or altitude of an object over sea level. The higher the altitude is measured the lower the atmospheric pressure. Through a static port on the outside of the aircraft, the atmospheric pressure is measured using an aneroid altimeter. The pilot adjusts the altimeter to the proper local barometric pressure to remain aware of their current altitude.

What Is a Radar Altimeter

A radar altimeter system transmits a radio wave to the ground and measures the time it takes to be reflected back up to the aircraft. The altimeter provides the pilot the distance to the ground directly below it, versus the barometric altimeter which provides the altitude between the aircraft and sea level.

rt1438 sdc cv3807 apn-232

Duotech has extensive test and repair capabilities for the Receiver/Transmitter and Signal Data Converter components of the AN/APN-232

What Is an APN-232 Airborne Navigation Radar

The AN/APN-232 CARA is a solid state radar altimeter system. In the Joint Army-Navy Nomenclature System, APN stands for A – Piloted Aircraft, P – Radar, N – Navigation Aid. CARA is the acronym for Combined Altitude Radar Altimeter. The CARA is the United States Air Force’s standard altimeter.

The APN-232 consists of two antennas under the nose in the forward equipment bay, a receiver/transmitter, a signal data converter, and an indicator. The system also provides analog and digital outputs to aircraft avionics systems like the computer or the head-up display, HUD.

Its Receiver-Transmitter (R/T) RT-1438 transmits a signal through the antennas to the earth’s surface, receives the reflected signal, processes the information, and provides the resulting altitude-related data from 0 to 50,000 feet to various avionics systems. To interface the R/T with a multitude of electrical interfaces in different aircraft, it possesses a Signal Data Converter (SDC) CV-3807. The SDC is designed to eliminate potential data freeze that might occur during in-flight emergency power switching.

APN-209 Radar Altimeter System

Since 1975, the APN-209 has been installed in helicopters like AH-1F, UH-1V, CH-47D, OH-58C/D, and H-60. Like the APN-232, the APN-209 provides the pilot a warning when the aircraft is at or below an altitude position set by the pilot. The radar altimeter enables the military to fly helicopters and airplanes very low over the land and the sea. This helps the aircraft to avoid radar detection and being targeted by anti-aircraft guns or surface-to-air missiles.

8 Facts About the APN-232 CARA

  1. Low Probability of Intercept (LPI) – LPI makes it difficult to be detected by passive radar detection equipment
  2. Improves Pilots Situational Awareness – the APN-232 can be easily interfaced with a Ground Proximity Warning Systems (GPWS) that warns a pilot when an aircraft is in immediate danger of flying into the ground. This type of system is sometimes referred to as Terrain Avoidance and Warning Systems (TAWS)
  3. Traffic. Traffic. Climb, Climb. – The APN-232 can be interfaced with a Terminal Collision Avoidance Systems (TCAS), a proximity alert device that alerts a pilot to other air traffic so they can avoid collisions
  4. Antijam capability – As important as it is to know your altitude to the object beneath or in front of you, it is also important to keep that capability from being jammed by the enemy.
  5. Very Popular – The CARA is the USAF’s standard altimeter and there have been over 11,000 CARA systems delivered.
  6. Operational Capability – provides altitude-related data from 0 to 50,000 ft.
  7. Operational Aircraft – The APN-232 CARA is used in C-5, C-17, C-130, OC-135, C-141, F-16, and F-15. The Receiver-Transmitter (part number 8010000653-6) is used on all CARA equipped aircraft except the F-16. The F-16 uses Receiver-Transmitter part number 8010000788-1
  8. Repaired/Maintained – Capabilities for repair and maintenance through Duotech Services, an AS9100 certified repair depot

Extensive Test and Repair Capabilities for APN-232 and APN-209

Duotech has extensive test and repair capabilities for the Receiver/Transmitter and Signal Data Converter components of both the AN/APN-232 and AN/APN-209. Even with tight funding and rising repair costs from the OEM, systems like the digital signal converter and receiver/transmitters radios of radar altimeters must be maintained to ensure mission-critical components are ready to keep those fighters in the air.

AS9100 certified, Duotech supports existing legacy and obsolete systems in aircraft like the F-15, F-16, and F-5 enabling operators to avoid scraping repairable equipment, while delivering under budget and meeting critical deadlines. Duotech provides repair services of electronic components for a variety of fixed wing and rotary wing aircraft systems. You can begin your Part Number Search or request a repair quote from Duotech today.


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