Air Data and Inertial Reference Unit

Also from: ADIRU

There are 3 identical ADIRUs that each consist of 2 independent parts:

an ADR [Air Data Reference] part which receives information from probes and sensors, and supplies barometric altitude, speed, mach, angle of attack, temperature, and overspeed warnings
an IR [Inertial Reference] part which supplies attitude, flight path vector, track, heading, acceleration, angular rates, ground speed, vertical speed, and aircraft position to the FMGC, EFIS, and others

ADIRU 1 supplies the captain's EFIS, and ADIRU 2 supplies the first officer's EFIS. ADIRU 3 is a standby for either system via the SWITCHING panel.

Control is through the ADIRS panel, the MCDUs, and the SWITCHING panel. The ADIRS panel is also known as the MSU [Mode Selector Unit] .

The ADIRU gives true heading instead of magnetic heading:

above 82° N
above 73° N between 90° and 120° W
above 60° S

Alignment

Select NAV position on the 3 IR [Inertial Reference] selectors to start the alignment. The ON BAT light illuminates for a few seconds as a test of the battery circuit. Alignment takes about 10 min, but the ECAM only displays the count down from 7 min. After about 30s, attitude information is displayed on the PFDs. The present position must be entered in the INIT page of the MCDU. The position may be fine tuned, and then the position is sent to the ADIRS by selecting the ALIGN IRS prompt.

Fast Alignment

Momentarily select the mode selectors to OFF, and within 5s reselect NAV.

Accuracy check

Compare raw data from tuned navaids with FM computed data. Must be carried out when:

GPS PRIMARY LOST message (IRS only navigation)
LOW accuracy displayed on the PROG page of the MCDU
NAV ACCUR DOWNGRAD message

Selected navaids should be displayed on the ND. Off track navaids can be used by inserting them into the PROG page on the MCDU. An error < 3nm is considered acceptable, and the FM to be reliable.

Categories: Airbus A330 | Navigation | ADIRS