Definition
An adjustment in a gear train that removes backlash by holding the meshing gear teeth in firm contact with each other, with no free play between them.
Plain English
A small built-in pressure that keeps two meshing gears pressed tightly together so they cannot wiggle or slap against each other when the load changes.
Context Anchor
Seen in landing gear inspection, maintenance, and rigging procedures, especially on retractable landing gear.
Derivation
‘Preload’ literally means a load applied before normal operation begins. The gears are loaded against each other ahead of time, so the first real working force does not have to take up any slack first.
Why Pilots Care
Correct preload prevents strut bottoming, maintains proper aircraft attitude on the ground, and reduces risk of damage on landing.
Analogy
It is like tightening a latch just enough that the door stays firmly shut before wind or movement tries to shake it open.
Intuition Check
Gear preload is not the weight of the aircraft sitting on the landing gear. It is the built-in force set in the gear mechanism before normal loads act on it.
Example Sentence 1
During the accessory case overhaul, the mechanic adjusted the gear preload to eliminate any backlash between the drive gears.
Example Sentence 2
Insufficient gear preload caused the main struts to bottom out during a firm landing on a rough runway.