(aviation) The primary landing gear of an aircraft, generally located slightly behind the aircraft's center of mass (or slightly ahead of it on a taildragger aircraft) and carrying the majority of the aircraft's weight.

plural of wing gear

plural of main gear

plural of arresting gear

plural of spur gear

A gear in a vehicle transmission which, when selected, enables the vehicle to move in the opposite direction, or backwards. / A gear fitted to a machine which allows it to run backwards.

(rail transport) Equipment for applying sand onto rails, to aid adhesion in slippery conditions.

plural of reverse gear

(mechanical engineering) The simplest type of gear, with teeth projecting radially, parallel to its axis.

(aviation, military) A system used to quickly decelerate a landing aircraft, essential for landing on an aircraft carrier (although land-based airfields can also be equipped with arresting gear); the most common system consists of a series of transverse wire ropes designed to snag an aircraft's tailhook, connected to a hydraulic or mechanical energy-absorbing system, but other systems exist (typically only for use in an emergency situation) which use a net to slow down an aircraft.