Definition
A reference line painted or marked on the airspeed indicator (or noted in the Pilot's Operating Handbook) showing the maximum speed at which the landing gear can be safely retracted after takeoff. Operating below this speed during retraction keeps loads on the gear doors, actuators, and structure within design limits.
Plain English
A speed mark that tells you the fastest you can be going when you raise the landing gear without risking damage to it.
Context Anchor
Seen in discussions, inspections, and troubleshooting of retractable landing gear hydraulic systems.
Derivation
Gear comes from an older word meaning equipment or apparatus. Line originally meant a cord or narrow path; in aircraft systems, it often means a hose, tube, or routed path that carries fluid, air, or electrical power. So a gear up line is the routed fluid path used when the landing gear is moving up.
Why Pilots Care
Raising the gear below this speed can cause a sudden loss of climb performance or allow the airplane to settle back onto the runway; the line supplies a clear, repeatable limit that protects both safety and gear mechanism limits.
Intuition Check
Do not read line as a painted mark or checklist line here. In this context, line means a hose, tube, or passage that carries hydraulic fluid.
Example Sentence 1
After liftoff and a positive rate of climb, he checked that airspeed was below the gear up line before selecting gear up.
Example Sentence 2
The procedure called for checking that the airspeed had reached the gear up line before moving the gear handle to the up position.