Definition
Air data computers are electronic units that take raw inputs from the aircraft's pitot-static system and outside air temperature probe, then calculate and output processed air data values such as pressure altitude, indicated airspeed, true airspeed, Mach number, vertical speed, and static air temperature. In RVSM-equipped aircraft, two independent ADCs feed the altimetry system to ensure the precise altitude-keeping required for operations in reduced vertical separation airspace.
Plain English
Small onboard computers that take pressure and temperature readings from outside the aircraft and turn them into the altitude, airspeed, and other air-related numbers shown to the pilot and used by autopilot and altitude-reporting systems.
Context Anchor
Seen in instrument flying and RVSM discussions, especially where accurate altitude keeping and altitude reporting are required.
Derivation
"Air data" refers to information derived from the air around the aircraft — its pressure, temperature, and movement past the aircraft. A "computer" here means a dedicated processing unit, not a general-purpose machine. Together: a box that crunches air-related measurements into useful flight numbers.
Why Pilots Care
In RVSM airspace, accurate altitude output from the ADC is essential for maintaining the reduced vertical separation between aircraft.
Intuition Check
Do not think of an ADC as a general computer like a laptop or tablet. In this context, it is a dedicated aircraft system that calculates flight data from air pressure and temperature inputs.
Example Sentence 1
Before dispatch into RVSM airspace, the crew confirmed both air data computers were operational and showed agreeing altitude readings.
Example Sentence 2
A failed ADC will usually cause the airspeed and altitude indications to disagree between the pilot and copilot displays.