11.retractable-gear. Retractable Landing Gear
A retractable landing gear stows the wheels into the fuselage, wings, or engine nacelles during flight to reduce parasite drag. The drag reduction increases cruise speed, improves climb performance, and lowers fuel consumption for a given true airspeed. These benefits come at the cost of added weight, mechanical complexity, higher maintenance, increased insurance, and a new category of pilot error — the gear-up landing.
System Types
Most light single- and twin-engine airplanes use one of two retraction systems:
- Electrohydraulic — An electric motor drives a hydraulic pump that pressurizes fluid to actuate the gear. Pressure is held by check valves; a pressure switch cycles the pump as needed. Found in the Piper Arrow, Mooney later models, and most Cessna retractables.
- All-electric — An electric motor drives a transmission and pushrods or torque tubes that mechanically extend and retract the gear. Found in the Beech Bonanza and Baron.
A few aircraft use engine-driven hydraulic pumps (typical in larger twins and turbine airplanes), with an electric auxiliary pump for backup and emergency extension.
Components and Indications
A typical retractable system includes:
- A gear selector handle, usually shaped like a wheel and located on the lower instrument panel, distinct from the flap handle (which is shaped like a wing).
- Position indicator lights — three green lights (one per gear leg) confirm down and locked. A red light or red-striped handle indicates the gear is in transit or unsafe. No lights typically means up and locked.
- A gear warning horn that sounds when the throttle is retarded below a preset manifold pressure (typically around 12–14 in. Hg) with the gear not down and locked, and often when flaps are extended beyond a certain setting with the gear up.
- Squat switches (also called safety or weight-on-wheels switches) on one or more gear struts that prevent gear retraction while the airplane's weight is on the wheels.
Operating Speeds
Two airspeed limitations apply, both published in the POH and marked on the airspeed indicator only by reference (no color arc):
- V_LO (maximum landing gear operating speed) — the maximum speed at which the gear may be extended or retracted. V_LO for retraction is sometimes lower than V_LO for extension because of the airloads on the gear doors during retraction.
- V_LE (maximum landing gear extended speed) — the maximum speed at which the airplane may be flown with the gear extended.
Exceeding these speeds can damage gear doors, actuators, and uplocks.
Normal Procedures
Retraction after takeoff: Retract the gear only after a positive rate of climb is established on the altimeter and VSI, and when a safe landing on the remaining runway is no longer possible. Retracting too early invites a gear-up landing if the engine fails on the runway; retracting too late wastes climb performance.
Extension on approach: Extend the gear at a consistent, briefed point — commonly abeam the touchdown point in the pattern, or at glideslope intercept on an instrument approach. Verify three green lights before continuing the approach.
The GUMPS check is the standard pre-landing flow:
- G — Gas (fuel selector on proper tank, boost pump as required)
- U — Undercarriage (gear down, three green)
- M — Mixture (rich)
- P — Propeller (high RPM / full forward)
- S — Switches/Seatbelts (lights, harnesses)
GUMPS should be performed at least twice on every approach — typically on downwind and again on final.
Emergency Extension
If the gear fails to extend normally, the POH emergency procedure must be followed exactly. Common methods include:
- A hand pump to manually pressurize the hydraulic system.
- A free-fall valve that releases hydraulic pressure and allows gravity (and aerodynamic forces, sometimes assisted by yawing the airplane) to drop the gear into place.
- A mechanical hand crank that drives the gear motor's transmission directly.
After emergency extension, the gear is typically not re-retractable in flight. Confirm three green indications, plan for a stabilized approach, and notify ATC. If only some gear legs extend, the POH will dictate whether to land gear-up, land partial-gear, or troubleshoot further.
Common Errors
Gear-up landings are overwhelmingly caused by distraction and broken habit patterns, not mechanical failure. Contributing factors include traffic conflicts, go-arounds, unfamiliar fields, and skipping the GUMPS check. The defense is a disciplined, verbalized flow performed at the same point on every approach, plus a final short-final glance at the gear handle and three green lights before crossing the threshold.