Transition to Complex Airplanes

Additional Training Required

Complex Airplanes

Definition: An airplane with retractable landing gear, flaps, and a controllable pitch propeller, including airplanes equipped with an engine control system consisting of a digital computer and associated accessories for controlling the engine and propeller, such as a full authority digital engine control (FADEC).

Regulation: No person may act as PIC of a complex airplane unless he or she has received ground and flight instruction from an authorized flight instructor and has received a one-time proficiency endorsement in his or her logbook. The flight training must be performed in a complex airplane, or in a full flight simulator or flight training device that is representative of a complex airplane.

Training Subjects: The instructor must determine that the pilot is proficient in the operation and systems. No specific subjects are stated.

Exemptions: This training and endorsement are not required if the pilot has logged flight time as PIC in a complex airplane before August 4, 1997.

Secondary Flight Controls

Secondary flight controls may consist of spoilers, wing flaps, leading-edge devices, and trim systems.

Wing Flaps

Wing flaps are movable panels on the inboard section of the trailing edges of the wings. They are hinged so that they may be extended down into the flow of air beneath the wings to increase both lift and drag.

Flaps work primarily by changing the airfoil's camber, which increases the wing's lift coefficient (C_L).

Extending the wings flaps:

• Increases drag.
• Lowers the stall speed.
• Increases the angle of incidence.
• Increases the wing's washout (wing roots stall first on planes with inboard flaps).

Benefits of the Flaps

Wing flaps can:

• Shorten the takeoff and landing distance required.
• Increase forward visibility by allowing a lower-pitch attitude.
• Generate more lift at slower airspeed, enabling the airplane to fly slower.
• Produce greater drag which permits a steeper angle of descent during landing.

Effect of the Flaps

Flap deflection of up to 15° primarily produces lift with minimal drag. The increased camber from flap deflection moves the center of pressure (lift) rearward, producing a nose-down force. The nose-down pitching moment, however, is offset by the airplane's tendency to balloon up.

Flap deflection beyond 15° produces a large increase in parasite drag. Most high-wing airplanes tend to pitch nose up because the resulting downwash increases the airflow over the horizontal tail.

Types of Flaps

Plain flaps provide a simple means of changing the camber of the wing. A higher camber produces the same amount of lift at a slower airspeed.

Split flaps also produce the same amount of lift at a slower airspeed due to an increase in camber, but because of the turbulent air pattern produced behind the airfoil, it also creates more drag than the plain flap.

Slotted flaps have a gap between the wing and the flap. When the flap is lowered, high-energy air moves through the slot and over the flap's upper surface. The slot's high-energy air accelerates the upper surface boundary layer and delays airflow separation, providing a higher CL than the split or plain flaps.

Fowler flaps travel both aft and down on tracks ti increase both the camber of the wing and the effective wing area. This combination allows slower and more stable flight than any other flap.

Flap Operating Limitations

When the flaps are extended, the airspeed should be at or below the airplane's maximum flap extended speed (V_FE). If they are extended above this airspeed, the force exerted by the airflow may result in damage to the flaps. If the airspeed limitations are exceeded unintentionally with the flaps extended, they should be retracted immediately regardless of airspeed.

Power Instrumentation

Tachometer

The tachometer is calibrated in hundreds of RPM and directly indicates the engine and propeller RPM. The red line on the tachometer indicates the maximum allowable RPM and the RPM required to obtain the engine's rated horsepower.

Fixed-Pitch Propeller: RPM is regulated by the throttle, which controls the engine's fuel/air flow. At a given altitude, the higher the tachometer reading, the higher the power output of the engine.

Constant-Speed Propeller: The propeller control sets the engine and propeller RPM. The selected RPM is maintained automatically by a governor.

Manifold Absolute Pressure

On airplanes equipped with a constant-speed propeller, power output is indicated by a manifold absolute pressure (MAP) gauge, usually in inches of mercury (Hg). It measures the pressure of the fuel/air mixture inside the intake manifold.

Normal Manifold Pressure Indications

Engine Off: The MAP gauge indicates ambient air pressure, 29.92" Hg. Local altimeter settings are corrected to indicate sea-level pressure; therefore, MAP is usually lower than the altimeter setting (1" Hg lower per 1,000').

After Start (Engine Idling): MAP is less than ambient pressure. Pistons moving within the cylinders pull air through the intake system and around the throttle valve, essentially creating a vacuum.

Takeoff: On takeoffs from low-elevation airports, the manifold pressure may exceed the RPM. This is normal. The AFM/POH contains any limitations.

Increasing Throttle: More fuel and air enter the engine, causing MAP to increase.

RPM Changes with a Constant Throttle Setting: Increasing engine RPM increases the velocity of the intake air, causing MAP to decrease slightly. The opposite is true when decreasing RPM.

Turbocharged Engines: With the wastegate closed on a turbocharged engine, increasing RPM increases MAP and vice-versa. An increase in engine RPM increases the turbine speed; therefore, MAP increases.

Operational Concerns

Excessive manifold pressure raises the cylinder pressure and temperatures, resulting in high stresses within the engine. A combination of excessively high manifold pressure and low RPM can induce detonation.

To avoid excessive manifold pressure:

• When increasing power, increase the RPM first (propeller control) and then the manifold pressure (throttle control).
• When decreasing power, decrease the manifold pressure first (throttle control) and then the RPM (propeller control).

Operating "Oversquare"

The performance charts in the AFM/POH should be consulted when selecting power settings. The combinations of RPM and manifold pressure listed in the charts have been flight tested and approved by the manufacturer. Therefore, if there are power settings, such as 2,100 RPM and 24" manifold pressure in the power chart, they are approved for use.

Principles of Propellers

Propeller Twist: When a propeller rotates, the outer parts of the blades travel faster than the portions near the hub. "Twisting" or variations in the geometric pitch of the blades permit the propeller to operate with a relatively constant AOA along its length when in cruising flight.

Blade Angle: Blade angle, usually measured in degrees, is the angle between the chord of the blade and the plane of rotation and is measured at a specific point along the length of the blade. Because the blade "face" of most propellers is flat, the chord line is often drawn along the face.

Pitch: The pitch is the distance in inches, which the propeller would screw through the air in one revolution if there were no slippage. A propeller designated as a "74-48" would be 74 inches in length and have an effective pitch of 48 inches.

Pitch is not the blade angle, but because pitch is largely determined by blade angle, the two terms are often used interchangeably. An increase or decrease in one is usually associated with an increase or decrease in the other.

Propeller Angle of Attack: The angle at which this air (relative wind) strikes the propeller blade is its AOA. It is the product of two motions: propeller rotation about its axis and its forward motion. The air deflection produced by the propeller blade on the engine side creates greater than atmospheric pressure. Thus thrust is produced.

Lift versus drag curves indicate that the most efficient AOA is small, varying from 2° to 4°. The actual blade angle necessary to maintain this small AOA varies with the aircraft's forward speed.

Slippage: Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch. Geometric pitch is the theoretical distance a propeller should advance in one revolution; effective pitch is the distance it actually advances. Thus, geometric or theoretical pitch is based on no slippage, but actual or effective pitch includes propeller slippage in the air.

For any speed of rotation, the horsepower absorbed by the propeller balances the horsepower delivered by the engine. On average, thrust constitutes approximately 80% of the torque (total horsepower absorbed by the propeller). The other 20% is lost in friction and slippage.

Propeller Mounting: The propeller is usually mounted on a shaft, which may be an extension of the engine crankshaft. In this case, the RPM of the propeller is the same as the crankshaft RPM.

Propeller efficiency decreases rapidly as the blade tips approach the speed of sound. By the use of reduction gearing, the engine can operate at a higher RPM than the propeller to develop more power. This prevents the propeller efficiency from decreasing.

Forces Acting on a Propeller in Flight

Centrifugal force causes the most stress. It pulls the propeller blades from the hub and is greater at faster speeds.

Thrust bending force causes the propeller blades to bend forward at the tips due to the high thrust produced.

Torque bending force causes the propeller blades to bend against the direction of rotation.

Aerodynamic twisting moment causes the propeller blades to twist to a higher angle. It is caused by the center of lift being ahead of the center of rotation.

Centrifugal twisting moment causes the propeller to twist to a lower angle. It is an opposing force of greater magnitude to the aerodynamic twisting moment. It is caused by all parts of the blade being forced around the same plane of rotation.

Counterweights are attached to the shank of each propeller blade on a multi-engine airplane. They tend to drive the blades to a lower angle. Inertia, or apparent force (centrifugal force) acting through the counterweights, is generally slightly greater than the other aerodynamic forces.

Spring pressure or charged air is used on constant-speed propeller systems. Depending on the aircraft type, the blades are under constant pressure to move them towards a higher angle (multi-engine airplanes) or lower angle (single-engine airplanes). Oil pressure is used to overcome this force.

Constant-Speed Propellers

A constant-speed propeller is a controllable-pitch propeller whose blade angle (pitch) is automatically varied in flight by a governor. The governor maintains a constant propeller RPM despite varying air loads by varying the pitch.

Performance Benefits

A constant-speed propeller is more efficient than a fixed-pitch propeller because it allows for the selection of the most efficient propeller RPM for the phase of flight.

Performance During the Takeoff Roll

An airplane equipped with a constant-speed propeller has better takeoff performance than a similarly powered airplane equipped with a fixed-pitch propeller. This is because the airplane can develop its maximum rated horsepower (red line on the tachometer) while motionless.

During takeoff, when maximum power and thrust are required, the propeller is at a low propeller blade angle (low pitch–high RPM). The low blade angle keeps the AOA small to allow the propeller to handle a smaller mass of air per revolution. This light load allows the engine to turn at high RPM and to convert the maximum amount of fuel into heat energy in a given time.

Climb Performance

After liftoff, the propeller automatically changes to a higher blade angle as the aircraft's speed increases. The higher blade angle increases the mass of air handled per revolution. This decreases the engine RPM, reduces fuel consumption and engine wear, and keeps thrust at a maximum.

Cruise Performance

In level flight, less power is required to produce a higher airspeed than is used in climb. Consequently, engine power is reduced by lowering the manifold pressure and increasing the blade angle (to decrease RPM). The higher airspeed and blade angle enables the propeller to handle a greater mass of air per second. Propeller efficiency is at or near maximum efficiency.

RPM Sensing and Control

Propeller Governor: The propeller control lever in the cockpit is connected to a propeller governor unit, which is essentially a speed-sensing element. It compares the actual propeller speed against the RPM setting made by the pilot. Adjustments to the propeller's speed are made by using engine oil to hydraulically move a cylinder, which, in turn, adjusts the propeller blade angle.

Blade Angles: The desired propeller RPM is maintained by varying the propeller blades' pitch (angle) to compensate for varying engine loads. The blade angle range for constant-speed propellers varies from about 11° to 40°. The higher the speed of the airplane, the greater the blade angle range.

Governing Range: The governing range is defined by the limits of the propeller blades' travel between high and low blade angle pitch stops. Changes in power settings (manifold pressure) and flight attitudes do not cause a change in RPM if the changes are within the governor's operating range.

Pitch Limits: Mechanical stops in the pitch change mechanism limit travel in both the high and low pitch directions. If the propeller blades contact a pitch stop, the engine RPM increases or decreases, as appropriate, with changes in airspeed and propeller load.

Propeller Governor Components

Cockpit Control: A push-pull cable is typically used to connect the propeller control to the governor. The cockpit control adjusts the tension on the speeder spring that exerts a force on the flyweights.

Oil Pump: A gear-type pump operated by the movement of the crankshaft connection boosts the engine oil pressure within the governor to the approximate 200–300 psi needed to control the propeller.

Relief Valve: A relief valve system regulates the operating oil pressure in the governor. The relief valve returns unneeded oil to the inlet of the governor's oil pump. This is normal during an on-speed condition when oil flow and oil pressure are constant.

Pilot Valve: Located in the center of the crankshaft, the pilot valve directs oil to or from the propeller by the movement of a piston. The piston can also assume a neutral position to stop all oil flow.

Fly Weights: "L" shaped weights are used to sense propeller speed and adjust the position of the pilot valve accordingly. During propeller rotation, centrifugal force exerts an outward force on the flyweights. The speeder spring opposes the outward movement.

Speeder Spring: Located on top of the flyweights, it opposes the centrifugal force exerted on the flyweights. The tension of the speeder spring sets the maximum RPM of the engine in the governor mode.

Propeller Governor Operation

To control the blades' pitch, a hydraulic piston-cylinder element is mounted on the front of the propeller blades inside the spinner. The high-pressure oil supply to or from the governor hydraulically actuates the piston when a blade angle change is needed. Mechanical connections from the piston transmit the linear piston motion to rotate each propeller blade.

On Speed: When the forces are in balance, no propeller speed adjustment is needed—no oil moves to or from the piston.

Overspeed Sensed: When the propeller rotation becomes too fast, the force of the flyweights overcomes the tension of the speeder spring. A pilot valve attached to the spring and flyweights then changes position to allow oil to move through the governor system. The change in oil pressure causes the propeller blades to continually move towards a high pitch–low RPM angle until the rotational speed slows enough to balance the flyweight and speeder spring pressures once again.

Underspeed Sensed: When the propeller rotation becomes too slow, the tension of the speeder spring overcomes the force of the flyweights. The pilot valve moves to allow oil to pass through the governor system. The change in oil pressure causes the propeller blades to continually move towards a low pitch–high RPM angle until the rotational speed increases enough to balance the flyweight and speeder spring pressures.

Loss of Oil Pressure

Multi-engine and single-engine airplanes have differing fail-safe needs if a loss of high-pressure oil occurs. Therefore, the governor's internal workings and the pitch change mechanism in the propeller dome depend on the type of airplane.

Multi-Engine Airplanes: The system is designed to move the propeller blades to a feathered position after a loss of oil pressure. This reduces drag.

Single-Engine Airplanes: The propeller blades move to a low pitch–high RPM position when oil pressure is removed by the force of a spring. Drag on the windmilling propeller is high, but its rotation can aid in restarting the engine if necessary.

Governor Operation on Single-Engine Airplanes

When the propeller control handle is moved forward, oil pressure to the piston is reduced, causing the blades to move to a low pitch–high RPM (unfeathered) position. Blade movement is aided by the natural centrifugal twisting moment of the blades and the spring.

When the propeller control handle is moved aft, oil pressure is increased to the piston causing the blades to move to a high pitch–low RPM position. Oil pressure to the piston is needed to overcome the tension of the spring and the natural centrifugal twisting moment of the blades.

Single-Engine Governor Operation

Governor Operation on Multi-Engine Airplanes

When the propeller control handle is moved forward, oil pressure is increased to the piston. The propellers move to a low pitch–high RPM position. The oil pressure must overcome the spring/charged air force and force created by the counterweights.

When the propeller control handle is moved aft, oil pressure to the piston is reduced by the propeller governor. The propellers move to a high pitch–low RPM position by the spring/charged air force and the aerodynamic forces acting on the counterweights.

Multi-Engine Governor Operation

Operational Concerns

• All power changes should be made smoothly and slowly to avoid overboosting or overspeeding.
• The tachometer reading should come up to within 40 RPM of the red line as soon as full power is applied and remain there for the entire takeoff.

• The green arc on the tachometer indicates the normal operating range. When developing power in this range, the engine drives the propeller. Below the green arc, the windmilling propeller is turning the engine. Prolonged operation could be detrimental to the engine.

• A momentary propeller overspeed may occur when the throttle is advanced rapidly for takeoff. This is usually not serious if the rated RPM is not exceeded by 10% for more than 3 seconds.

Constant-Speed Propeller Checks

Constant-speed propellers have additional checks to perform before takeoff, which may include:

• Propeller cycling/exercising
• Propeller governor system check (sometimes an optional procedure)
• Propeller feathering check [AMEL]

Exercising the Propeller Blade Changing Mechanism

Caution: Oil tends to thicken, especially in cold weather. If the propeller isn't exercised before takeoff, there is a possibility that the engine may overspeed when power is applied.

During the run-up, the propeller is operated slowly and smoothly through a complete cycle to:

• Verify the system is working correctly.
• Circulate warm oil through the propeller governor system.

To exercise the propeller:

1. Move the propeller control to the high pitch–low RPM position.
2. Allow the RPM to stabilize.
3. Move the propeller control back to the low pitch–high RPM position.

Propeller Governor System Check

To check the propeller governor:

1. Retard the propeller control drop of 100drop −200 RPM is observed.
2. Advance the throttle to increase manifold pressure slightly. Ensure the RPM remains steady.
3. Return the propeller to the takeoff position (high pitch–low RPM).

An alternative check of the propeller governor:

1. Start with the throttle at idle and with the propeller control fully aft (low pitch–high RPM).
2. Advance the throttle slowly. Ensure the RPM increases until the propeller governing range is reached.
3. In the propeller governing range, the RPM should no longer increase. Ensure the RPM remains steady while advancing the throttle slightly.

1. Return the throttle to idle, then move the propeller to the takeoff position (high pitch–low RPM).

Magneto Checks

During the engine run-up, verify the operation of each magneto by turning the other magneto OFF.

Considerations for the magneto check:

• Did the engine shut down?
• If one magneto is not operating, selecting the other will cause the engine to shut down.

• An RPM drop is normal when swapping from BOTH to any single magneto.
• No decrease on a single magneto indicates that one magneto is not operating or something is preventing the magneto from turning off.

• Limits are specified to ensure the magnetos will provide sufficient power in the event of a single magneto failure in flight.

• Differential checks ensure that both magnetos are operating at the same level of performance ("sharing the work").

• A 50–100°F EGT rise is normal when operating on a single magneto due to the lengthed duration of the fuel/air mixture combustion process.

Magneto Checks with a Constant-Speed Propeller

A constant-speed propeller must be in the governing range for the propeller governor to keep the RPM constant. At lower RPM settings, such as during the magneto check, the constant-speed propeller reacts like a fixed-pitch propeller.

Hydraulic System

Hydraulics is a branch of science that deals with the transmission of power by incompressible fluids under pressure. A hydraulic system is often used on small airplanes to operate wheel brakes, retractable landing gear, and constant-speed propellers.

System Fluid

Hydraulic system liquids are used primarily to transmit and distribute forces to various units to be actuated. Liquids can do this because they are almost incompressible. Hydraulic operations are nearly 100% efficient, with only negligible loss due to fluid friction.

Small aircraft predominantly use MIL-H-5606, a mineral oil-based hydraulic fluid to operate wheel brakes, retractable landing gear, and some constant-speed propellers. Phosphate ester-based fluids, mainly the name-brand "Skydrol," are used in most transport category aircraft and are highly fire-resistant.

Hydraulic Fluid Compatibility

Hydraulic fluids are not always compatible. To ensure proper system operation and avoid damage to the hydraulic system's nonmetallic components, the correct fluid must be used as specified in the aircraft manufacturer's maintenance manual.

Some of the fluids that are interchangeable with MIL-H-5606 include:

• MIL-H-6083: A rust-inhibited version of MIL-H-5606
• MIL-H-83282: A more flame-resistant fluid than MIL-H-5606, but generally limited to -40°F

Safety Considerations

Skin contact should be avoided with all fluid types. MIL-H-5606 and Skydrol are minimally irritating to the skin upon direct contact. Prolonged exposure can cause itching, rashes, and secondary infections from bacteria.

System Types

A distinction must be made between fluid flow and pressure to understand the types of hydraulic systems. Flow refers to the amount of fluid being moved in a certain period. Pressure is the force exerted on a fluid, which doesn't necessarily need to be flowing. There will be no system pressure if there are no flow restrictions on fluid through the hydraulic system.

Open-Center: A system having fluid flow but no pressure when the actuating mechanisms are not moving. A pump continuously circulates fluid from the reservoir, through the selector valves, and back to the reservoir. A restriction will be placed on the fluid to increase its pressure only when needed to operate an aircraft system.

Closed-Center: A system where the fluid is constantly under pressure as long as the pump operates normally. This has the advantage of fluid pressure being available when it is needed to operate an aircraft system. This system type is required on aircraft with hydraulically actuated flight controls.

System Components

Reservoirs: The reservoir is a tank in which an adequate fluid supply for the system is stored. Fluid flows from the reservoir to the pump, where it is forced through the system and eventually returned to the reservoir. It also serves as an overflow basin for excess fluid forced out of the system by thermal expansion.

Pumps: Pumps supply the fluid flow required for the operation of hydraulic devices. All aircraft hydraulic systems have one or more power-driven pumps, either engine-driven or electrically powered. A hand pump may be provided as a backup.

Common types of pumps:

• Gear-Type: Gear-type pumps are constant-displacement-type pumps that use meshing gears to pump fluid. They can be used on low-pressure systems (under 1500 psi) but are generally unsuitable for high-pressure applications.

• Constant-Displacement, Piston-Type: Piston-type pumps utilize a piston moving in a cylinder to pressurize a fluid. A constant-displacement pump moves a specific amount of fluid with each stroke. The hydraulic system must have a pressure regulator or relief valve to control fluid pressure.

• Variable Displacement, Piston-Type: This is the most common type of pump on large aircraft. A variable-displacement design pump uses a built-in system pressure regulator to compensate for system demand changes by increasing or decreasing the fluid output.

Valves: Flow control valves control the speed and direction of fluid flow in the hydraulic system. They provide for the operation of various components when desired and the speed at which the component operates.

Common types of valves:

• Sequence valves control the sequence of operation between two branches in a circuit. An example of a sequence valve is in an aircraft landing gear actuating system.
• Priority valves provide fluid to critical hydraulic subsystems when pressure is low.
• Hydraulic fuses detect a sudden increase in fluid flow, such as a burst downstream. If it detects such an event, it shuts off the flow.

• Selector valves control the direction and movement of a fluid. They provide for the simultaneous flow of fluid into and out of the unit.
• Check valves allow fluid to flow unimpeded in one direction but prevent or restrict it in the opposite direction.

• Pressure relief valves limit the amount of pressure exerted on a confined liquid. This prevents component failure or rupturing of fluid lines under excessive forces.

Accumulators: An accumulator is a steel device divided into two chambers. One chamber contains hydraulic fluid at system pressure, and the other is charged with nitrogen or air.

The function of an accumulator is to:

• Dampen pressure surges in the hydraulic system.
• Aid or supplement the power-driven pump when several units are operating at once.
• Store pressure for the limited operation of a hydraulic unit.
• Compensate for small internal or external (not desired) leaks to prevent the system from continually cycling due to the pressure switches kicking in.

Actuators: An actuator, or servo, is a cylindrical device that transforms fluid pressure into a mechanical force. A typical actuating cylinder contains hydraulic fluid, one or more pistons, and fluid seals. A piston is moved by high-pressure fluid forward and backward within the cylinder.

Actuating cylinders are of two major types. A single-action actuating cylinder can produce powered movement in one direction only. A double-action actuating cylinder is necessary to operate components such as the landing gear that move in two directions (e.g., extension and retraction).

The basic operating principle of an actuator is based on Pascal's Law, which states that the pressure in an enclosed container is transmitted equally and undiminished to all points of the container, and the force acts at right angles to the enclosing walls.

Filters: Filters clean the hydraulic fluid, preventing foreign particles and contaminating substances from remaining in the system. They can be located within the reservoir or in the fluid lines. A bypass valve located in the lines opens if the filter gets clogged.

Hydraulic Power Packs

A hydraulic power pack is a small, self-contained hydraulic system powered by an engine gearbox or electric motor. It is used when a single aircraft control, such as the landing gear, requires hydraulic actuation.

Power Pack Components

The power pack contains the components of a traditional hydraulic system: a reversible pump, a filter, high-and-low pressure control valves, a thermal relief valve, and a shuttle valve. The actuator(s) can be internal or external.

Power Pack Operation: Landing Gear Extension

1. The electric motor turns the pump so that high-pressure fluid flows to the gear-down side of the actuating cylinders.
2. Pump pressure moves the spring-loaded shuttle valve to the left to allow fluid to pass.

1. High-pressure fluid entering the actuator moves the piston. The gear begins to extend by a mechanical linkage to the piston rod. The nosewheel is lighter, so restrictors are used in its actuator ports to slow down the fluid.
2. Fluid from the upside of the actuators returns to the reservoir through the gear-up check valve.

1. When the gear is fully extended, pressure builds in the gear-down line from the pump, and the low-pressure control valve unseats to return the fluid to the reservoir.
2. Electric limit switches turn off the pump when the gear is down and locked.
3. Mechanical locks hold the gear in the extended position.

Power Pack Operation: Landing Gear Retraction

1. The electric motor turns the pump in the opposite direction so that high-pressure fluid flows through the gear-up check valve and to the gear-up sides of the actuating cylinders.
2. As the pistons begin to move, the mechanical down locks are released.
3. Fluid from the gear-down side of the actuators returns to the reservoir through the shuttle valve and filter.

1. When the gear is fully retracted, pressure builds in the gear-up line from the pump, and the pressure switch is opened to cut electric power to the pump. If the pressure switch fails to shut off the pump, the high-pressure relief valve opens to prevent excessive pressure from building in the hydraulic system.

1. The gear is held in the retracted position with hydraulic pressure. If pressure declines, the pressure switch closes to run the pump. Pressure builds until the pump is cut off again by the opening of the pressure switch.

Operational Concerns for Hydraulic Systems

Overheating: When the system exceeds its maximum allowable operating temperature.

Loss of Pressure: A loss of system pressure can occur by losing fluid or pump failure.

Fluid Contamination: Contamination of the fluid can be caused by improper servicing, including using incompatible fluids, or by a component failure.

Cavitation: When there is not enough pressure in the reservoir to force the fluid to the pump's inlet, the pump picks up air instead of fluid. This is known as cavitation.

These threats can all result in the damage or failure of an individual system component or a complete loss of the hydraulic system. Thorough preflight inspections and proper servicing of the hydraulic system are the best prevention.

Landing Gear

Retractable Landing Gear Safety Devices

A squat switch prevents the gear from being retracted while the aircraft is on the ground. One method of prevention is to disable the gear position selector physically. When the landing gear is compressed, a lock-pin protrudes through the landing gear control handle so that it cannot be moved to the up position. After takeoff, the pin retracts, permitting the gear to be raised.

Most airplanes with retractable landing gear have a gear warning horn that sounds when the airplane is configured for landing and the gear is not down and locked. The horn is typically activated by sensors connected to the throttle position, flap position, or the airspeed indicator.

Warning lights/indicators are typically provided in the flight deck to show the pilot when the wheels are down and locked (green light), when they are up and locked, or if they are in intermediate positions (red or amber light).

Retractable Landing Gear Limitations

• The landing gear must not be operated above the maximum landing gear operating speed (V_LO). Operating at a higher airspeed may cause damage to the operating mechanism.
• When the gear is down and locked, the airplane should not be operated in excess of the maximum landing gear extended speed (V_LE).

Safety Considerations for Retractable Landing Gear

In order to minimize the chances of a landing gear-related mishap:

• Use an appropriate checklist.
• Consider the warning horn an "action horn." When it sounds, action is required to correct the problem (e.g., apply power or extend the gear).
• Be familiar with the emergency gear extension procedures for the airplane.

• Be familiar with the warning horn and warning light systems for the particular airplane. Use the horn system to cross-check the warning light system when an unsafe condition is noted.
• Review the procedure for replacing light bulbs in the warning light displays. 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 system.

Stall-Related Definitions

Stall: An aerodynamic condition that occurs when smooth airflow over the airplane's wings is disrupted, resulting in a loss of lift and an increase in drag. The wing does not entirely stop producing lift, but it is not capable of sustaining level flight.

A stall occurs when the airplane is flown at an angle of attack (AOA) greater than the angle for maximum lift (the critical AOA). This can occur at any airspeed, in any attitude, with any power setting.

Some aircraft do not have a defined stall break. The stall is characterized as more of a "mush." In such cases, a stall can be characterized by any of the following: (1) buffeting, (2) a lack of pitch authority, (3) a lack of roll control, or (4) an inability to arrest the descent rate (e.g., pitch control full aft).

Buffeting: The beginning of airflow separation over the wing creates a turbulent wake. If the horizontal stabilizer or stabilator is in the turbulent separation wake, vibrations in the flight controls (buffeting) can be felt.

First Indication of a Stall: The initial aural, tactile, or visual sign of an impending stall, such as buffeting or the activation of a stall warning device.

Stall Speed

The speed at which the critical angle of attack is exceeded is the stall speed. The term can be misleading because stall speeds listed in the AFM/POH are not constants.

Published stall speeds are valid only:

• In unaccelerated 1 G flight.
• In coordinated flight.
• At one power setting (typically idle).
• At one weight (typically maximum gross weight).
• At a particular CG (typically maximum forward location).

A stall is the result of excessive AOA, not insufficient airspeed.

Stall Prevention Training

Stall prevention training consists of ground and flight instruction to avoid and recognize an impending stall.

Preflight Planning and Inspections

Preflight planning can prevent many of the precursors to stall/spin accidents, including:

• Fuel exhaustion/starvation.
• Inadequate climb performance due to overloading.
• Reduced stability due to an excessively aft CG.
• Inadvertent encounters with instrument weather conditions.

A careful preflight inspection should be conducted to ensure:

• The fuel is not contaminated by water (to prevent an engine failure on takeoff).
• The dynamic and static pressure ports are clear to prevent erroneous airspeed indications.
• The aircraft is free of ice, snow, and frost.

Contributing to the accident was the pilot's inadequate preflight weight and balance calculations, which resulted in the center of gravity being aft of the limit. NTSB Stall/Spin Accident Report (WPR16LA150)

Defined Minimum Maneuvering Speed

Pilots of transport category airplanes are familiar with the term minimum maneuvering speed, which is the slowest allowable speed to make turns in a specific aircraft configuration or at a certain weight. But manufacturers of small, general aviation airplanes do not publish minimum maneuvering speeds.

For an aircraft without a published minimum maneuvering speed, is it up to the pilot to decide what margin above stall speed to use during turning flight. By designating and adhering to a defined minimum maneuvering speed (DMMS), general aviation pilots can hold themselves to a higher level of safety by reducing the risk of loss of control-inflight (LOC-I) accidents.

The following formula defines a minimum maneuvering speed.

DMMS = Clean Stall Speed (V_S1) × 1.4

The DMMS is essentially a 30% buffer above the clean stall speed (V_S1) in a 30° bank. Stall speed increases by approximately 7% to 8% in 30° bank (1.3 V_S1 + 8% = roughly 1.4).

Times when it is acceptable to go slower than the DMMS:

• During takeoff and climbout.
• On a base leg and configuring for landing (partial flaps and 1.4 V_S0 is recommended).
• On final approach (the published speed or 1.3 V_S0 is recommended).
• During intentional slow flight at a safe altitude.

Best Practices for Using a Minimum Maneuvering Speed

• If the aircraft has a traditional airspeed indicator ("steam gauges"), mark the DMMS with a piece of removable tape.
• When flying with passengers, inform them of the DMMS and encourage them to speak up if it is violated.
• Do not confuse the DMMS with the design maneuvering speed (V_A). DMMS is a minimum. V_A is a maximum.

• Know how the DMMS relates to the airplane's best glide speed (V_G). Understand the importance of each.
• For a multi-engine airplane, consider how the DMMS relates to the minimum control speed (V_MC).

Scenario-Based Stall Training

Scenario-based training prepares pilots for real-world stall events that happen unexpectedly. When possible, scenarios should include accident or incident data to provide a realistic learning experience.

The following scenarios can be recreated at a safe altitude for training purposes. Emphasis should be placed on stall avoidance and recognition.

Engine Failure After Takeoff

In the event of an engine failure on initial climb-out, the airplane is at or near a stalling AOA. At the same time, the pilot may still be holding right rudder. The pilot must immediately lower the nose (get "light in the seat") to prevent a stall while moving the rudder to ensure coordinated flight.

This scenario demonstrates how quickly a stall can occur in a climb attitude following an engine failure. If the pilot is not mentally prepared for such an event, the startle factor may prevent any action from being taken in the first 3–4 seconds. In that amount of time, the airplane could stall.

To simulate this scenario:

1. Establish an obstacle clearance configuration at the best angle of climb (V_X).
2. Close the throttle to simulate an engine failure.
3. Maintain back-pressure on the pitch control to hold the pitch attitude.
4. Take no action for four seconds to simulate the startle factor. Note the amount of airspeed lost.
5. Recover at the first indication of a stall by reducing the AOA (throttle would not be available).

"Impossible Turn" Stall

Attempting to return to the airport after an engine failure during climbout often results in an uncoordinated, accelerated stall. The tendency is for the pilot to use inside rudder pressure to increase the turn rate without increasing the bank angle. The result is often a cross-controlled stall and spin ending in fatalities, which is the reason why critics call it the "impossible" turn.

To simulate this scenario:

1. Establish a normal climb configuration at the best rate of climb (V_Y).
2. Close the throttle to simulate an engine failure.
3. Pitch down to establish the best glide speed.
4. Make a 180° turn using a bank angle of approximately 40°.
5. Optionally, apply inside rudder pressure and opposite aileron to simulate a cross-controlled condition.

1. To clear a simulated obstacle, attempt to maintain altitude for five seconds while turning.
2. Recover at the first indication of a stall by reducing the AOA (throttle would not be available). Then roll the wings level.

How to Recover from a Spin

There is no universal spin-recovery technique that works for all aircraft. The aircraft's particular spin characteristics are listed in the AFM/POH. In the absence of the manufacturer's recommended spin recovery procedures and techniques, the "PARE" recovery procedure is recommended.

Stability Demonstrations

The following demonstrations can be performed to experiment with stability. The purpose is to show that the airplane is designed to be stable in each axis.

Pre-Maneuver Checks for all Stability Demonstrations

• Clear the area
• Heading established and noted
• Altitude established
• Position near a suitable emergency landing area
• Set power and aircraft configuration:
• Trim and stabilize the flightpath before each demonstration

• Do not exceed V_A or V_O
• Do not change the power setting or aircraft configuration during a demonstration

Transfer Controls: The instructor or the learner can do the flying. If the learner is flying, the instructor states what control inputs to perform.

Longitudinal Stability (Pitch) – Demonstration

This is a demonstration of a long-period pitch oscillation called a phugoid.

Discussion:

• The airplane tends to maintain the trimmed angle of attack (AOA). Throughout the phugoid, the AOA remains almost constant.
• The airplane is cyclically trading airspeed and altitude (potential and kinetic energy) during the oscillations.

Considerations:

• Use the rudder and ailerons to keep the airplane coordinated and the wings level. Be careful not to disturb the pitch oscillation.
• The faster the airplane is flown, the longer the period.

Procedure:

1. Pitch up gently to lose approximately 20 knots, avoiding a stall.
2. With the nose high, release the pitch control.
3. Note that the nose will start down, indicating positive static stability.
4. When the speed increases beyond the trim setting, the nose will begin to rise.
5. Note the decreasing amplitude (height) of each oscillation, indicating positive dynamic stability.

1. The airplane will eventually settle at the original flight attitude, airspeed, and altitude.

Lateral Stability (Roll) – Demonstration

This demonstration compares the effects of roll stability in shallow, medium, and steep turns.

Discussion:

• An airplane with positive lateral stability tends to roll back toward level flight when a wing drops.
• Too much lateral stability can limit the airplane's ability to roll into a normal turn.
• In steep banks, roll forces due to the overbanking tendency overcome the airplane's ability to roll back toward level flight.
• A slip may progress into a spiral dive, but it is easily correctable by an alert pilot.

Considerations:

• Pitch and yaw inputs are not used until the recovery process.
• Small variations between left and right turns will result due to the torque effect.

Procedure:

• Enter a shallow, slipping turn (15° bank or less) to the right or left and then neutralize the ailerons:
• Note that the airplane slowly tries to roll wings level, indicating positive static stability.
• Return to level flight.

1. Note that the bank angle remains relatively constant, indicating a balance of forces.
2. Return to level flight.

1. Note that the airplane slowly continues to roll into the turn, the beginning of a spiral divergence.
2. Allow spiral to develop within the airplane's limitations.
3. Note that the ball/brick (skip-skid indicator) remains essentially centered, indicating the tail is aligning the airplane into the relative wind (directional stability).

1. Optionally, roll the wings level and then release the controls to observe a recovery phugoid.
2. Return to level flight.

Directional Stability (Yaw) – Demonstration

This demonstration shows the airplane's strong directional stability that keeps the nose in front of the tail.

Discussion:

• With the rudder deflected, the aircraft tries to roll in the direction of the yaw. This is caused by a combination of dihedral effect and roll due to one wing moving faster than the other (overbanking tendency).
• Simultaneous, full control inputs are not considered when determining V_A.

Considerations:

• Perform this demonstration at a speed well below V_A.

Procedure:

1. Enter a flat turn using the rudder only. Use opposite aileron control to keep the wings level.
2. Note the increased pedal force as rudder deflection increases.
3. Quickly return the rudder and aileron controls to neutral.
4. Note the airplane's immediate tendency (positive static stability) to yaw back into alignment with the relative wind.
5. Note the overshoots and damping (positive dynamic stability).

The Risk Management Process

1. Identify Hazards (Perceive): Identify conditions, events, objects, or circumstances that could lead to or contribute to an accident.

2. Assess the Risk (Process): Determine the probability and severity of an accident that could result from the hazards.

3. Mitigate the Risk (Perform): Investigate strategies and tools that reduce, mitigate, or eliminate the risk.

The 3P Model

The 3P model offers a simple, structured method for pilots to manage risk during flight phases.

To use the 3P model, the pilot:

1. Perceives the given set of circumstances for a flight.
2. Processes by evaluating the impact of those circumstances on flight safety.
3. Performs by implementing the best course of action.

Once the 3P's are completed, the process begins again. With practice, the cycle becomes a smooth, efficient habit.

Managing Priorities During Emergencies

"Aviate, navigate, communicate" is a phrase used by pilots to remember the priorities of tasks during emergencies.

The priorities are:

1. Aviate: Maintaining positive aircraft control has priority over all other considerations, including airplane configuration and checklists.
2. Navigate: Know where you are and where you intend to go.

1. Communicate: Let someone know your position and intentions on the emergency radio frequency (121.5 MHz) or by contacting a nearby ATC facility. If already in radio contact with a facility, do not change frequencies unless instructed to change.

Checklist Usage During Emergencies

Aircraft checklists are typically divided into normal and emergency procedures. Manufacturers may publish emergency checklists in an abbreviated form, followed by amplified (expanded) checklists that provide additional information.

Immediate Action Items

Certain emergencies require immediate action on the pilot's part. Airplane manufacturers typically denote immediate action items in a checklist with a bold font and place them before the less critical items.

During an emergency, pilots should perform the immediate action items from memory and then refer to the written checklist.

Abnormal Powerplant Operation in Flight

Caution: Locate a suitable landing area immediately in case it is needed.

Loss of Manifold Pressure

Loss of RPM During Cruise

Loss of Airspeed During Cruise

Fluctuating or Low Oil Pressure

Fluctuation or reduction of oil pressure is cause for immediate action. Even though the engine may appear to be operating normally, catastrophic failure may be imminent.

Propeller Overspeed

.

The airspeed necessary to maintain level flight with a propeller overspeed may differ from the best glide speed. A further reduction in airspeed may allow for continued safe flight and landing.

Landing Gear Malfunction

Indications:

• Landing gear fails to extend or retract
• Gear disagreement light or gear in transit light remains illuminated

Possible Causes:

• Landing gear motor failure
• Tripped landing gear motor circuit breaker
• Electrical or hydraulic system failure

Corrective Actions:

• Take no action until the aircraft is at a safe altitude and location
• Attempt a manual gear extension procedure using the manufacturer's checklist
• Do not exceed the maximum landing gear extension speed (V_LE) if the landing gear does not fully retract

If the gear fails to extend:

• Attempt to force the gear down by gravity:
• Dive the airplane (in smooth air only) to the maximum speed and execute a rapid pull up within the positive limit load factor
• Induce alternating yaw inputs to shake the gear loose (avoid rapid control inputs and do not exceed V_A or V_O)

• Select an airport with crash and rescue services (runway foam if available)
• Notify airport and emergency personnel
• Consider burning off excess fuel to reduce the landing speed and fire potential
• Do not overly fixate on saving a propeller or engine from damage ("the airplane now belongs to the insurance company")
• Anticipate control problems upon touchdown if the gear extended differentially

Flap Malfunction

Indications:

• Flaps fail to extend or retract
• Flaps partially extend or retract
• Flaps extend or retract differentially (asymmetric flaps)

Possible Causes:

• Flap motor failure
• Tripped flap motor circuit breaker
• Damage to the cables or push-rods

Corrective Actions:

• Check the flaps motor circuit breaker if the flaps are electrically operated
• Do not exceed the maximum flap extension speed (V_FE) if the flaps do not fully retract

If the flaps are extended differentially (asymmetric flaps):

• Rudder pressure will be required to counteract yawing tendencies
• Anticipate roll control problems
• Avoid landing with a crosswind from the side of the airplane with the greatest flap extension
• Fly at a faster-than-normal airspeed during the approach and landing

If the flaps fail to extend fully:

• Consider flying a wider, longer traffic pattern to avoid picking up excessive speed in the descent
• Plan a higher touchdown speed and longer landing roll (up to 50% more runway needed)
• Anticipate a nose-high attitude and reduced forward visibility on final approach
• Anticipate floating during landing:
• Do not force the airplay onto the runway
• Do not flare excessively