Definition
On a Primary Flight Display (PFD), short colored lines that extend from the current value indicators on the airspeed and altitude tapes to show the predicted airspeed or altitude six seconds into the future based on the current rate of change. They are a type of trend indicator used to anticipate where the airplane will be if the present trend continues.
Plain English
Small colored lines on the glass-cockpit airspeed and altitude tapes that show where those values will be in about six seconds if nothing changes. They give the pilot a heads-up on what's coming, not just what's happening now.
Context Anchor
Seen while scanning an electronic flight display, especially near airspeed, altitude, and other changing flight indications.
Why Pilots Care
They let the pilot spot and correct trends early, producing smoother control inputs and fewer large deviations.
Intuition Check
Do not treat colored lines as decoration. In this context, the color and line position are part of the instrument information and are meant to help you interpret what the airplane is doing.
Example Sentence 1
As the airplane approached the assigned altitude, the pilot watched the colored line on the altitude tape shrink toward zero and began reducing pitch to level off smoothly.
Example Sentence 2
Watching the heading colored line allowed the pilot to apply a small correction before the actual course deviation grew large.