Landing gear is one of the most mechanically complex and safety-critical systems on any aircraft. At its simplest, gear serves three fundamental purposes: supporting the aircraft during ground operations, absorbing the energy of landing, and providing directional control during taxi, takeoff, and rollout. How that gear is arranged — and whether it stays exposed to the airstream or tucks away during flight — shapes an aircraft's performance, maintenance demands, and certification requirements from the ground up.
For airframe technicians and student pilots alike, understanding the difference between fixed and retractable configurations is not merely academic. The FAA Airframe written test and practical exam both probe this knowledge directly, and a thorough grasp of both systems helps technicians troubleshoot correctly, inspect methodically, and return aircraft to service with confidence.
Fixed Landing Gear: Simplicity as a Feature
Fixed landing gear, as the name implies, remains permanently extended and exposed throughout all phases of flight. The main structural components are attached rigidly — or through spring steel, rubber biscuits, or tubular aluminum shock-absorbing legs — to primary airframe structure such as the fuselage bulkheads or wing spars. Because there are no actuating mechanisms, no hydraulic or electric retraction systems, and no gear doors, the overall system is mechanically simpler and lighter in smaller aircraft.
The most common shock-absorbing designs seen on fixed-gear light aircraft include spring steel legs, used prominently on Cessna singles, where the leg itself flexes to absorb landing loads; rubber biscuit or donut shock absorbers, common on older Piper and Beechcraft designs; and oleo pneumatic struts, which use compressed air and hydraulic fluid to cushion touchdown loads. Even though fixed gear lacks retraction hardware, the shock struts and attachment fittings still require careful inspection. Technicians must verify proper strut extension (measured as exposed chrome), check for fluid leaks, inspect tires for wear and proper inflation, and examine wheel bearings during every 100-hour and annual inspection.
The principal aerodynamic drawback of fixed gear is parasitic drag. The exposed wheels, struts, and fairings (wheel pants) create significant frontal area. On a typical light single, fixed gear may account for roughly 10 to 20 percent of the aircraft's total parasite drag, noticeably reducing cruise speed and increasing fuel consumption compared to an equivalent retractable-gear design. Wheel fairings (also called gear leg fairings or speed fairings) reduce this penalty substantially, and their installation, security, and condition are required inspection items — a missing or cracked fairing is more than cosmetic; it alters drag, can vibrate destructively, and on some designs can interfere with steering.
Retractable Landing Gear: Performance with Complexity
Retractable landing gear systems raise the wheels into enclosed bays in the fuselage or wings after takeoff, dramatically reducing parasite drag and enabling higher cruise speeds, improved fuel efficiency, and greater useful range. This performance gain comes at the cost of substantially increased complexity, weight, and maintenance burden.
A typical retractable system consists of several integrated subsystems: an actuating power source (hydraulic, electric, or a combination), mechanical linkages and drag braces (also called side braces or jury struts) that lock the gear in both the up and down positions, gear doors that close over the wheel wells to restore aerodynamic smoothness, position indicating lights (green for down-and-locked, red or no light for unsafe/in-transit, sometimes a separate indication for gear-up), and warning systems that alert the crew if the throttle is reduced toward landing configuration with the gear still retracted.
Hydraulically-actuated systems use an engine-driven or electric hydraulic pump to move fluid through selector valves and actuating cylinders. Electrically-actuated systems use electric motors driving screwjacks or cables. Many light retractable-gear aircraft use an electric motor-driven system (as found on many Piper Arrows and Beechcraft Bonanzas) with an emergency extension capability — typically a free-fall/gravity drop or a hand pump, with some designs using other means — in case of primary system failure; technicians should always consult the specific type's maintenance manual for the actual emergency extension method installed.
Up-locks and down-locks are among the most critical components in the system. Down-locks hold the gear positively in the extended position so that it cannot collapse on landing. Up-locks hold the gear retracted so it does not fall out in flight due to aerodynamic loads or gravity. Both must be rigorously inspected for security, wear, and correct adjustment. The drag brace — a folding strut that goes over-center when the gear is down — is the primary mechanical down-lock on many designs and must be checked for proper over-center travel during every inspection.
Gear Configurations: Tricycle vs. Conventional (Tailwheel)
Beyond fixed versus retractable, landing gear is also classified by the arrangement of wheels relative to the aircraft's center of gravity. The two primary configurations are tricycle (nosewheel) and conventional (tailwheel or taildragger).
In the tricycle configuration, two main gear legs are positioned aft of the center of gravity and a single nosewheel is located forward. This arrangement offers inherently stable ground handling: any deviation from the intended path produces a corrective moment that tends to realign the aircraft with its direction of travel. Visibility over the nose is improved during taxi. Most modern training aircraft use tricycle gear for these handling advantages.
In the conventional configuration, two main gear legs are located forward of the center of gravity and a small tailwheel or tail skid is at the aft fuselage. Because the center of gravity is aft of the main wheels, a ground loop tendency exists — any lateral deviation can rapidly amplify because the CG wants to swing around ahead of the main gear. Conventional gear aircraft require more precise directional control during takeoff and landing rollout. Structurally, however, conventional gear is simpler, lighter, and often better suited to rough, unimproved strips because the propeller has greater ground clearance.
A third configuration — the tandem arrangement, with main gear aligned fore and aft along the centerline — is used on certain military and high-performance aircraft (such as the U-2 reconnaissance aircraft) and is rarely encountered in civilian maintenance.
Why It Matters: Safety, Airworthiness, and the Gear-Up Landing
The gear-up landing remains one of the most preventable and costly accidents in general aviation. The FAA's Airplane Flying Handbook notes that gear-up landings most often result from distraction during the approach, a malfunctioning warning system that was not noticed, or a non-standard situation that broke the pilot's normal checklist flow. From a maintenance perspective, technicians play a direct role in prevention: a properly rigged and tested gear warning horn, verified position indicator lights, and an emergency extension system confirmed to operate correctly can mean the difference between an embarrassing but survivable incident and a catastrophic accident.
For AMT airframe students, 14 CFR Part 43 governs maintenance and inspection requirements for landing gear systems. Major repairs and major alterations to landing gear — such as welding a cracked gear leg, modifying the retraction system, or changing tire or wheel assemblies outside approved limits — require sign-off under Part 43 Appendix A and, in many cases, FAA approval via a Form 337. Technicians must reference the aircraft manufacturer's maintenance manual and the Type Certificate Data Sheet (TCDS) for approved components, tire sizes, and strut servicing specifications.
Key Numbers and Rules
- Oleo strut servicing: Proper strut extension is specified in the aircraft maintenance manual; typically measured as the exposed chrome length. Incorrect inflation (too high or too low) changes shock absorption characteristics and can alter aircraft weight-and-balance or trigger abnormal tire wear.
- Tire pressure: Must be maintained within the range specified in the maintenance manual and TCDS. Under-inflation causes excessive heat buildup and sidewall damage; over-inflation reduces the contact patch and increases the risk of blowout on landing.
- Gear warning systems: Under the legacy 14 CFR Part 23 rule, 14 CFR 23.729 requires an aural warning for retractable-gear aircraft that must sound when the aircraft is in a landing configuration (typically low throttle setting) with the gear not down-and-locked; the amended (post-2017) Part 23 uses consensus/ASTM-based standards referenced through the rule to achieve equivalent safety objectives.
- Retraction system inspections: Actuator travel, down-lock over-center check, up-lock engagement force, and door rigging must be verified after any major work on the system and at each 100-hour/annual inspection.
- Emergency extension: The pilot's operating handbook (POH) and aircraft flight manual (AFM) specify the procedure. The technician must verify the system works correctly — activating the emergency extension should produce free-fall or manually-assisted extension and a positive down-and-locked indication.
Common Test Traps
- Conflating up-locks and down-locks: Test questions often ask which lock does what. Remember: down-locks keep gear extended for landing; up-locks keep gear retracted during flight. Confusing them when answering a question about system failure can lead to the wrong troubleshooting path.
- Assuming fixed gear needs no shock absorption inspection: Even spring steel gear legs flex and fatigue. FAA test items may describe a cracked or overstressed spring steel leg — the correct action is to consult the maintenance manual and replace or inspect per manufacturer criteria, never to assume fixed gear is maintenance-free.
- Misidentifying conventional vs. tricycle by wheel count alone: Both configurations can have three wheels. The distinction is the position of the CG relative to the main wheels and whether the third wheel is a nosewheel or tailwheel — a classic exam distractor.
- Over-center drag brace confusion: Many students think over-center means the brace is bent beyond 180 degrees. It means the pivot joint has traveled just past the straight-line position so that landing loads drive the brace further into the lock rather than folding it — a crucial mechanical distinction that appears on the airframe test.
- Gear door rigging as a cosmetic concern: Improperly rigged gear doors can jam the retraction mechanism, cause actuator overload, or prevent complete gear extension. They are structural and functional components — always treat rigging discrepancies as airworthiness issues, not appearance issues.