Undercarriage, commonly called landing gear in American English, is the assembly that supports an aircraft when it is not flying and enables ground movement for taxiing, takeoff and landing. The term appears frequently in aviation contexts and is used interchangeably with "landing gear" in many sources; see the aviation usage and how it attaches to an aircraft. It must withstand landing loads, provide steering and braking, and may retract to reduce aerodynamic drag.

Main types

  • Tricycle gear: a nose wheel and two main wheels; common on modern airplanes.
  • Taildragger (conventional): two main wheels ahead of the center of gravity and a tailwheel or skid.
  • Fixed gear: non-retractable, simpler and lighter but increases drag.
  • Retractable gear: folds into the airframe to improve cruise efficiency.
  • Specialized gear: floats for water operations, skis for snow, and skids for helicopters.

Key components include wheels and tires, brakes, shock-absorbing struts (often oleo-pneumatic), retraction mechanisms, steering linkages and mounting attachments. Supporting elements such as doors, actuators and locking systems protect the gear when stowed. Smaller aircraft may have simpler fixed spring or bungee arrangements; larger aircraft use hydraulics and complex uplocks.

Historically, early heavier-than-air craft used skids or simple wheels mounted to lightweight frames. As speeds and weights rose, designers introduced stronger oleo struts, braking systems and the tricycle layout for improved forward visibility and ground handling. Retractable gear became widespread as higher cruising speeds demanded reduced drag.

Operationally, the undercarriage is a primary safety item. Preflight inspections check tire condition, strut extension and hydraulic lines. Maintenance addresses corrosion, fatigue on attachment points, brake wear and correct retraction/extension timing. Failures may force rejected landings or emergency procedures but are mitigated by redundant systems and design margins.

Notable distinctions: "undercarriage" is more common in British English, while "landing gear" is the preferred American term. For more technical standards and regulatory guidance, consult type-specific manuals and regulatory material or authoritative references on ground operations.