Definition
An imaginary horizontal reference line drawn outward from each end of the artificial horizon symbol on the attitude indicator, used to compare the pitch and bank of the miniature aircraft against pitch ladder marks and other display elements during instrument scanning.
Plain English
It's the flat line on the attitude display, mentally stretched out past its edges, so you can quickly see how the airplane symbol is sitting against it — wings level or tilted, nose up or down.
Context Anchor
Seen on the attitude portion of an electronic flight display during instrument flying, especially while cross-checking the display for pitch and bank control.
Derivation
"Extended" here means stretched beyond its visible length. The line on the display is short, but the pilot mentally extends it across the screen to use it as a longer reference.
Why Pilots Care
Gives pilots an immediate, unbroken visual reference for attitude that supports precise control and reduces the chance of spatial disorientation.
Analogy
Like stretching a piece of tape straight across the inside of your windshield so your eye can instantly judge level flight.
Intuition Check
Do not think of this as the real horizon outside the airplane. It is a drawn reference on the instrument display; "extended" means the displayed line is made longer for easier viewing.
Example Sentence 1
During the radial cross-check, the pilot's eyes returned to the extended artificial horizon line between each glance at the surrounding instruments.
Example Sentence 2
During the climb, the extended artificial horizon line helped confirm the correct pitch attitude on the primary flight display.