Definition
A malfunction or loss of the Air Data Computer, the unit that processes pitot-static inputs (ram air pressure and static pressure) along with temperature data to calculate airspeed, altitude, vertical speed, and Mach number for the aircraft's displays and flight systems. When the ADC fails, the primary flight display may show invalid or flagged airspeed, altitude, and vertical speed indications, and dependent systems such as autopilot, autothrottle, and unusual attitude recovery protection may be degraded or unavailable.
Plain English
The small computer that turns outside air pressure and temperature into your airspeed and altitude readings has stopped working properly. The numbers on your speed and altitude displays can no longer be trusted, and any system that relies on those numbers may also stop working.
Context Anchor
Seen in glass-cockpit, autopilot, and unusual-attitude recovery discussions, where aircraft protection systems may depend on accurate air data.
Derivation
Air Data Computer literally means a computer for air data — the measurements taken from the air around the aircraft (pressure, temperature). Knowing this helps you understand why an ADC failure takes out airspeed, altitude, and vertical speed all at once: they all come from the same source.
Why Pilots Care
Loss of these indications removes primary references for pitch and power management in IMC, forcing immediate use of backup instruments or partial-panel techniques to prevent loss of control.
Intuition Check
Do not assume an ADC failure always means every display goes blank. It can also mean the displayed airspeed, altitude, or vertical-speed information is present but unreliable.
Example Sentence 1
After the ADC failure, the crew lost their primary airspeed and altitude indications and reverted to the standby instruments while requesting vectors back to the airport.
Example Sentence 2
During recurrent training the instructor simulated an ADC failure to practice maintaining level flight on partial panel.