Figure 12-10. Typical landing gear switch with combination amber and green. Another combination has a three light indicator.
Figure 12-11. Landing gear handles and single and multiple light indictor.
A landing gear safety switch, sometimes referred to as a squat switch, is usually mounted in a bracket on one of the main gear shock
struts. [Figure 12-12] When the strut is compressed by the weight of the airplane, the switch opens the electrical circuit to the motor
or mechanism that powers retraction. In this way, if the landing gear switch in the flight deck is placed in the RETRACT position
when weight is on the gear, the gear remains extended, and the warning horn may sound as an alert to the unsafe condition. Once the
weight is off the gear, however, such as on takeoff, the safety switch releases and the gear retracts.
Figure 12-12. Landing gear safety switch.
Many airplanes are equipped with removable safety devices to prevent collapse of the gear when the airplane is on the ground. These
devices are called ground locks. One common type is a pin installed in aligned holes drilled in two or more units of the landing gear
support structure. Another type is a spring-loaded clip designed to fit around and hold two or more units of the support structure
together. All types of ground locks usually have red streamers permanently attached to them to readily indicate whether or not they
are installed.
Emergency Gear Extension Systems
The emergency gear extension system lowers the landing gear if the main power system fails. Some airplanes have an emergency
release handle in the flight deck, which is connected through a mechanical linkage to the gear uplocks. When the handle is operated, it
releases the uplocks and allows the gear to free fall or extend under their own weight. [Figure 12-13]
On other airplanes, release of the uplock is accomplished using compressed gas, which is directed to uplock release cylinders. In
some airplanes, design configurations make emergency extension of the landing gear by gravity and air loads alone impossible or
impractical. In these airplanes, provisions are included for forceful gear extension in an emergency. Some installations are designed
so that either hydraulic fluid or compressed gas provides the necessary pressure, while others use a manual system, such as a hand
crank for emergency gear extension. [Figure 12-14] Hydraulic pressure for emergency operation of the landing gear may be provided
by an auxiliary hand pump, an accumulator, or an electrically-powered hydraulic pump depending on the design of the airplane.
Operational Procedures
Preflight
Because of their complexity, retractable landing gear demands a close inspection prior to every flight. The inspection should begin
inside the flight deck. First, make certain that the landing gear selector switch is in the GEAR DOWN position. Then, turn on the
battery master switch and ensure that the landing gear position indicators show that the gear is down and locked.
Figure 12-13. Typical emergency gear extension systems. Figure 12-14. Retractable landing gear inspection checkpoints.
External inspection of the landing gear consists of checking individual system components. [Figure 12-14] The landing gear, wheel
well, and adjacent areas should be clean and free of mud and debris. Dirty switches and valves may cause false safe light indications
or interrupt the extension cycle before the landing gear is completely down and locked. The wheel wells should be clear of an y
obstructions, as foreign objects may damage the gear or interfere with its operation. Bent gear doors may be an indication of possible
problems with normal gear operation.
Ensure shock struts are properly inflated and that the pistons are clean. Check main gear and nose gear uplock and downlock
mechanisms for general condition. Power sources and retracting mechanisms are checked for general condition, obvious defects, and
security of attachment. Check hydraulic lines for signs of chafing and leakage at attach points. Warning system micro switches (squat
switches) are checked for cleanliness and security of attachment. Actuating cylinders, sprockets, universal joints, drive gears,
linkages, and any other accessible components are checked for condition and obvious defects. The airplane structure to which the
landing gear is attached is checked for distortion, cracks, and general condition. All bolts and rivets should be intact and secure.
Takeoff and Climb
Normally, the landing gear is retracted after lift-off when the airplane has reached an altitude where, in the event of an engine failure
or other emergency requiring an aborted takeoff, the airplane could no longer be landed on the runway. This procedure, however, may
not apply to all situations. Preplan landing gear retraction taking into account the following:
⦁ Length of the runway
⦁ Climb gradient
⦁ Obstacle clearance requirements
⦁ The characteristics of the terrain beyond the departure end of the runway
⦁ The climb characteristics of the particular airplane
For example, in some situations it may be preferable, in the event of an engine failure, to make an off airport forced landing with the
gear extended in order to take advantage of the energy absorbing qualities of the terrain (see Chapter 18, “Emergency Procedures”).
In which case, a delay in retracting the landing gear after takeoff from a short runway may be warranted. In other situations, obstacles
in the climb path may warrant a timely gear retraction after takeoff. Also, in some airplanes the initial climb pitch attitude is such that
any view of the runway remaining is blocked, making an assessment of the feasibility of touching down on the remaining runway
difficult.
Avoid premature landing gear retraction and do not retract the landing gear until a positive rate of climb is indicated on the flight
instruments. If the airplane has not attained a positive rate of climb, there is always the chance it may settle back onto the runway with
the gear retracted. This is especially so in cases of premature lift-off. Remember that leaning forward to reach the landing gear
selector may result in inadvertent forward pressure on the yoke, which causes the airplane to descend.
As the landing gear retracts, airspeed increases and the airplane’s pitch attitude may change. The gear may take several seconds to
retract. Gear retraction and locking (and gear extension and locking) is accompanied by sound and feel that are unique to the specific
make and model airplane. Become familiar with the sound and feel of normal gear retraction so that any abnormal gear operati on can
be readily recognized. Abnormal landing gear retraction is most often a clear sign that the gear extension cycle will also be abnormal.
Approach and Landing
The operating loads placed on the landing gear at higher airspeeds may cause structural damage due to the forces of the airstream.
Limiting speeds, therefore, are established for gear operation to protect the gear components from becoming overstressed duri ng
flight. These speeds may not be found on the airspeed indicator. They are published in the AFM/POH for the particular airplane and
are usually listed on placards in the flight deck. [Figure 12-15] The maximum landing extended speed (VLE) is the maximum speed at
which the airplane can be flown with the landing gear extended. The maximum landing gear operating speed (V LO) is the
maximum speed at which the landing gear may be operated through its cycle.
Figure 12-15. Placarded gear speeds in the flight deck.
The landing gear is extended by placing the gear selector switch in the GEAR DOWN position. As the landing gear extends, the
airspeed decreases and the pitch attitude may change. During the several seconds it takes for the gear to extend, be attentive to any
abnormal sounds or feel. Confirm that the landing gear has extended and locked by the normal sound and feel of the system
operation, as well as by the gear position indicators in the flight deck. Unless the landing gear has been previously extended to aid in
a descent to traffic pattern altitude, the landing gear should be extended by the time the airplane reaches a point on the downwind leg
that is opposite the point of intended landing. Establish a standard procedure consisting of a specific position on the downwind leg at
which to lower the landing gear. Strict adherence to this procedure aids in avoiding unintentional gear up landings.
Operation of an airplane equipped with a retractable landing gear requires the deliberate, careful, and continued use of an appropriate
checklist. When on the downwind leg, make it a habit to complete the before-landing checklist for that airplane. This accomplishes
two purposes—it ensures that action has been taken to lower the gear and establishes awareness so that the gear down indicators can
be rechecked prior to landing.
Unless good operating practices dictate otherwise, the landing roll should be completed and the airplane should be clear of the
runway before any levers or switches are operated. This technique greatly reduces the chance of inadvertently retracting the landing
gear while on the ground. Wait until after rollout and clearing the runway to focus attention on the after-landing checklist. This
practice allows for positive identification of the proper controls.
When transitioning to retractable gear airplanes, it is important to consider some frequent pilot errors. These include pilots that have:
⦁ Neglected to extend landing gear
⦁ Inadvertently retracted landing gear
⦁ Activated gear but failed to check gear position
⦁ Misused emergency gear system
⦁ Retracted gear prematurely on takeoff
⦁ Extended gear too late
These mistakes are not only committed by pilots who have just transitioned to complex aircraft, but also by pilots who have
developed a sense of complacency over time. In order to minimize the chances of a landing gear-related mishap:
⦁ Use an appropriate checklist. (A condensed checklist mounted in view is a reminder for its use and easy
reference can be especially helpful.)
⦁ Be familiar with, and periodically review, the landing gear emergency extension procedures for the
particular airplane.
⦁ Be familiar with the landing gear warning horn and warning light systems for the particular airplane. Use the
orn system to cross-check the warning light system when an unsafe condition is noted.
⦁ Review the procedure for replacing light bulbs in the landing gear warning light displays for the particular
air
plane, if applicable, so that you can properly replace a bulb to determine if the bulb(s) in the display is
good. If bulbs are replaceable, check to see if spare bulbs are available in the airplane spare bulb supply as
part of the preflight inspection.
⦁ Be familiar with and aware of the sounds and feel of a properly operating landing gear system.
Transition Training
Transition to a complex airplane or a high-performance airplane should be accomplished through a structured course of training
administered by a competent and qualified flight instructor. The training should be accomplished in accordance with a ground and
flight training syllabus. [Figure 12-16]
This sample syllabus for transition training is an example. The arrangement of the subject matter may be changed and the emphasis
shifted to fit the qualifications of the transitioning pilot, the airplane involved, and the circumstances of the training situation. The
goal is to ensure proficiency standards are achieved. These standards are contained in the Airman Certification Standards for the
certificate that the transitioning pilot holds or is working toward.
Figure 12-16. Sample transition training syllabus.
The training times indicated in the syllabus are for illustration purposes. Actual times should be based on the capabilities of the pilot.
The time periods may be minimal for pilots with higher qualifications or increased for pilots who do not meet certification
requirements or have had little recent flight experience.
Chapter Summary
Flying a complex or high-performance airplane requires a pilot to further divide his or her attention during the most critical phases of
flight: takeoff and landing. The knowledge, judgment, and piloting skills required to fly these airplanes needs to be developed. It is
essential that adequate training is received to ensure a complete understanding of the systems, their operation (both normal and
emergency), and operating limitations.