Definition
A vacuum-sealed glass display tube in which a beam of electrons is fired from a heated cathode at the rear, steered by magnetic or electric fields, and made to strike a phosphor-coated screen at the front, producing a visible image. In aircraft, CRTs were the original technology used for electronic flight instrument displays such as the EFIS, EICAS, and ECAM screens before being replaced by liquid crystal displays (LCDs).
Plain English
A type of electronic screen — like the old, deep television sets — that creates a picture by firing a stream of tiny electrical particles at the back of the glass. In aircraft, these were the first electronic cockpit displays before flat-panel screens took over.
Context Anchor
Seen in older aircraft instrument, radar, weather radar, and avionics display descriptions, especially in maintenance manuals for legacy equipment.
Derivation
‘Cathode’ comes from the Greek kathodos, meaning ‘a way down’ — it refers to the negatively charged electrode that releases the electrons. ‘Ray’ refers to the beam of electrons, and ‘tube’ describes the sealed glass envelope they travel inside. Knowing this helps you picture what the device actually does: send a downward stream of electrons through a tube to paint an image on the screen.
Why Pilots Care
Maintenance technicians still encounter CRT displays in legacy aircraft. They behave differently from modern LCDs — they are bulkier, generate more heat, draw more power, and can suffer from issues like screen burn-in, focus drift, and high-voltage hazards during servicing.
Analogy
A CRT works like an old television or computer monitor: the picture is drawn on the inside of a glass screen rather than produced by a flat panel.
Intuition Check
Do not think of a CRT as just the screen image. The CRT is the physical tube assembly that creates the image.
Example Sentence 1
The technician removed the failed CRT from the captain's primary flight display and replaced it with an updated LCD unit during the avionics upgrade.
Example Sentence 2
Older navigation displays relied on a CRT to present range and bearing information to the crew.