Landing Gear Malfunction
Once the pilot has confirmed that the landing gear has in fact malfunctioned and that one or more gear legs refuses to respond to the conventional or alternate methods of gear extension contained in the AFM/POH, there are several methods that may be useful in attempting to force the gear down. One method is to dive the airplane (in smooth air only) to VNE speed (red line on the airspeed indicator) and (within the limits of safety) execute a rapid pull up. In normal category airplanes, this procedure creates a 3.8G load on the structure, in effect making the landing gear weigh 3.8 times normal. In some cases, this may force the landing gear into the down and locked position. This procedure requires a fine control touch and good feel for the airplane. Careful consideration should be given to the fact that if the pull up is too abrupt, it may result in an accelerated stall, possible loss of control, and cause excessive structural stress to be imposed on the aircraft.
The design maneuvering speed (VA) is a structural design airspeed used in determining the strength requirements for the airplane and its control surfaces. The structural design requirements do not cover multiple control inputs in one axis or control inputs in more than one axis at a time at any speed, even below VA. Combined control inputs cause additional bending and twisting forces. Any airspeed above the maneuvering speed provides a positive life capability that may cause structural damage if excessive G forces are exerted on the aircraft. VA is based on the actual gross weight of the airplane and the wing’s response to a 50 foot per second wind gust or movement of the elevator. The combination of turbulence and high G loading induces even greater stress on the aircraft. Because wind gusts are not symmetrical, the total additional stress that is added to the aircraft due to turbulence is difficult to determine. Each element of the airframe and each flight control component have their own design structural load limit. Maneuvering speed is primarily determined for the wings; the elevator may be structurally damaged below this speed.
An alternative method that has proven useful in dislodging stuck landing gear (in some cases) is to induce rapid yawing. After stabilizing below VA, the pilot should alternately and aggressively apply rudder in one direction and then the other in rapid sequence. However, be advised that operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time. The resulting yawing action may cause the landing gear to fall into place. The pilot must be aware that moving the rudder from stop to stop is not a load limit certification requirement for normal category airplanes. Only aircraft designed for certain high G load flight maneuvers must have a vertical fin and rudder capable to withstand abrupt pedal control application to the limits in both directions.
If all efforts to extend the landing gear have failed and a gear-up landing is inevitable, the pilot should select an airport with crash and rescue facilities. The pilot should not hesitate to request that emergency equipment is standing by.
When selecting a landing surface, the pilot should consider that a smooth, hard-surface runway usually causes less damage than rough, unimproved grass strips. A hard surface does, however, create sparks that can ignite fuel. If the airport is so equipped, the pilot can request that the runway surface be foamed. The pilot should consider burning off excess fuel. This reduces landing speed and fire potential.
If the landing gear malfunction is limited to one main landing gear leg, the pilot should consume as much fuel from that side of the airplane as practicable, thereby reducing the weight of the wing on that side. The reduced weight makes it possible to delay the unsupported wing from contacting the surface during the landing roll until the last possible moment. Reduced impact speeds result in less damage.
If only one landing gear leg fails to extend, the pilot has the option of landing on the available gear legs or landing with all the gear legs retracted. Landing on only one main gear usually causes the airplane to veer strongly in the direction of the faulty gear leg after touchdown. If the landing runway is narrow and/or ditches and obstacles line the runway edge, maximum directional control after touchdown is a necessity. In this situation, a landing with all three gear retracted may be the safest course of action.
If the pilot elects to land with one main gear retracted (and the other main gear and nose gear down and locked), the landing should be made in a nose-high attitude with the wings level. As airspeed decays, the pilot should apply whatever aileron control is necessary to keep the unsupported wing airborne as long as possible. [Figure 17-7] Once the wing contacts the surface, the pilot can anticipate a strong yaw in that direction. The pilot must be prepared to use full opposite rudder and aggressive braking to maintain some degree of directional control.
When landing with a retracted nosewheel (and the main gear extended and locked), the pilot should hold the nose off the ground until almost full up-elevator has been applied. [Figure 17-8] The pilot should then release back pressure in such a manner that the nose settles slowly to the surface. Applying and holding full up-elevator results in the nose abruptly dropping to the surface as airspeed decays, possibly resulting in burrowing and/or additional damage. Brake pressure should not be applied during the landing roll unless absolutely necessary to avoid a collision with obstacles.
If the landing must be made with only the nose gear extended, the initial contact should be made on the aft fuselage structure with a nose-high attitude. This procedure helps prevent porpoising and/or wheelbarrowing. The pilot should then allow the nosewheel to gradually touchdown, using nosewheel steering as necessary for directional control.