ALA-52B altitude or distance sensor

The Honeywell ALA-52B is a radar altimeter for aircraft that measures height above the reflecting surface beneath the aircraft. It is an avionics unit in the 3 MCU form factor, sold by Honeywell Aerospace, and works with separate transmit and receive antennas and an altitude indicator.

The operating range extends from -20 to 8,000 ft (-6.1 to 2,438 m). The negative lower limit allows the altitude reading to stay valid on the ground and during the last stage of landing. Accuracy is stated as plus or minus 1.5 ft (0.46 m) or 2%, whichever is greater, so the absolute error dominates at low height and the percentage term at greater height. The altimeter operates with roll angles up to plus or minus 40 degrees and pitch up to plus or minus 20 degrees, which sets the attitude envelope in which a valid reading can be expected.

The transmitter works in the 4.2 to 4.4 GHz band at a nominal output power of 1 W. Signal processing uses a fast Fourier transform approach with enhanced rejection of multipath and double-bounce returns, and the maker states that the unit filters 5G broadband interference. Software is developed to DO-178B Level A and the programmable hardware to DO-254 Level A. The design meets ARINC 707-6 and EUROCAE ED-30, and the maker cites FAA alternative means of compliance for listed Airbus and Boeing models.

For installation, the unit weighs 3.9 kg and operates between -55 and 70 °C. It takes 115 VAC at 380 to 420 Hz primary power, as is usual on large transport aircraft. Two antennas are required, one transmitting and one receiving, and a multifunction or dedicated indicator displays the altitude. The unit is compatible with a range of platforms, including the Airbus A318 to A321, A330 and A340 and Boeing 717, 737, 747, 757, 767, 777 and 787.

Typical applications are height-above-ground measurement for approach, landing and ground-proximity functions on large transport aircraft, and as a reference for a retrofit programme that replaces an older radar altimeter. Its weight and AC supply place it in the transport and large-aircraft class rather than small unmanned aircraft.