The Air Data Display Unit (ADDU) is a self-sensing, RVSM compliant, digital air data computing (DADC) Altimeter with selectable altitude alerting. The ADDU inputs static (Ps) and pitot (Pt) pressures, total temperature (Tt), and installation configuration data (from an installation configuration module, model 9B-03508).

Air data is output on ARINC 429 and RS422 data formats. The indicator provides a dedicated display of baro and SSEC corrected altitude, and altimeter setting number, selected altitude, in combination with an E/M pointer movement. The altimeter setting number can be selected for either in Hg or hPa units of measure. Units of measure are manually selected by pressing and holding the right-hand pushbutton until the desired value is shown (M/ft/inHg/hPa). A short press of the same button prompts a 29.92 inHg (1013 hPa) zero correction.

The ADDU’s LCD has high-intensity backlighting for daytime use, and low level white lighting for nighttime viewing. The ADDU provides altitude alert notifications using its ADDU-controlled ALT Alert Lamp.

The PWR flag will appear on the display if the primary power is not present and backup power is. The STBY flag indicates that a fault has occurred, resulting in reduced performance of the indicator. The “A” legend indicates a master altitude alerter for a dual ADDU installation. Pressing the recessed TEST pushbutton prompts a short display test and access to BIT results.

The ADDU has an altitude range of -1000 to +53,000 feet (16,154 meters), an airspeed range of 40 to 400 knots, and an ASN (baro) range of 22.00 to 31.00 inHg (745 to 1050 hPa).

The ADDU has an ALT SEL Button for setting the alert altitude and canceling altitude alert notifications, a BARO Knob for setting the ASN and changing altitude and ASN display units, and a TEST Button for activating its self-test and fault history displays.