Definition

An Air Data Inertial Reference Unit (ADIRU) combines functions of an Air Data Computer (ADC) and an Inertial Reference Unit (IRU) into a single unit.

Description

An ADIRU supplies air data such as airspeed, angle of attack, air temperature, and altitude, along with inertial reference data such as aircraft position, heading, groundspeed, and attitude, to Electronic Flight Instrument System (EFIS) displays and other systems on board modern glass-cockpit aircraft. Operation of engines, flight controls, landing gear, autopilot and other systems involve use of ADIRU data.

Normally, aircraft are equipped with at least two ADIRUs: one for the captain's flight displays, and another for the first officer's displays. A third ADIRU may be installed for redundancy in case of the failure of ADIRU 1 or ADIRU 2.

ADIRUs gather air data from sensors such as angle of attack sensors, total air temperature sensors, and air data modules, which convert pitot-static pressure into numerical data.

ADIRUs gather inertial reference data from ring laser gyros and accelerometers. Like other inertial reference systems, ADIRUs must go through an alignment process on startup. This initialization takes several minutes and must be completed while the aircraft is stationary. Initialization tells the system where the aircraft is located, which way is north, and which way the aircraft is pointed.