6 32 fcom sa227 landing gear

AIRCRAFT SYSTEMS

LANDING GEAR SA227‐ SERIES/FCOM/VTM 6.32.1 LANDING GEAR SYSTEM

Landing gear extension and retraction is electrically controlled and hydraulically actuated. The landing gear handle, located on the cockpit pedestal, is used to direct 28.5 VDC electrical power from the left essential bus to the landing gear selector valve located in the left nacelle over the wing.

The selector valve, when actuated, directs hydraulic pressure to the landing gear actuators for either retraction or extension of the gear, as selected. Two actuators are installed on each gear. Both actuators are used for gear retraction. Main hydraulic system pressure is directed to the left actuator on the nose gear and to the outboard actuators on the main gear during normal gear extension. During emergency extension of the gear, auxiliary hydraulic pressure is supplied to the right actuator on the nose gear and to the inboard actuators on the main gear.

As each gear is fully retracted, it engages a mechanical uplock hook. When the last of the three gear fully retracts, the electrical power is shut off to the selector valve. The selector valve moves to the closed (OFF) position, and the actuator lines are ported to return. As each gear moves to the fully extended (DOWN) position, its dual drag strut unfolds and the drag strut joints (or elbows) move to an overcenter position.

This overcenter position of the extended drag strut is locked by the mechanical interference between a bellcrank and roller strut. Normal hydraulic pressure is applied to the down side of the primary system actuator on each gear until the selector valve closes due to shutdown of both engines (causing loss of normal hydraulic pressure) or the electrical power is shut off.

When the emergency hand pump is used, hydraulic pressure is applied to the down side of the auxiliary system actuator on each gear. Emergency hand pump Pressure is not routed through the normal selector valve. The aircraft has the capability of free fall extension of the landing gear. The free fall can be supplemented by hand pumped hydraulic pressure in the event the gear does not lock down.

LANDING GEAR WARNING SYSTEM

The landing gear warning sonalert will sound if: 1. Any landing gear down and locked switch is not made, 2. And either power lever is at the flight idle gate, 3. Or if the flaps are more than half way down, regardless of power lever position.

The micro switches at the flight idle gate are adjusted to sound the sonalert at the gate and through power lever travel approximately 1/8 inch (3 mm) forward of the gate. That range corresponds to the range of flight idle power. Therefore, descents at flight idle power may be conducted in the clean configuration without the gear warning sounding by merely advancing the power levers slightly.

Some airplanes may be equipped with a gear warning mute button located on the pedestal aft of the power levers. Pushing the mute button will silence the landing gear warning. Advancing either power lever beyond the micro switch will reset the gear warning system. If the landing gear warning is generated because the wing flaps are more than half way down and any gear is not down and locked, the warning horn cannot be silenced by either power lever manipulation or the mute button (mute button not installed on TSM aircraft).

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS LANDING GEAR MAIN LANDING GEAR

SA227‐ SERIES/FCOM/VTM

6.32.2

Figure 6.32‐1

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

LANDING GEAR SA227‐ SERIES/FCOM/VTM 6.32.3 MAIN LANDING GEAR STRUTS

Each main landing gear strut essentially is two telescoping cylinders with enclosed ends. The two cylinders, when assembled together, form an upper and lower chamber. The chambers are separated from each other by a floating piston. The lower cylinder is serviced with nitrogen and the upper cylinder is serviced with hydraulic fluid. The upper chamber contains an orifice that divides it into two smaller chambers. The hydraulic fluid must pass through this orifice during compression of the nitrogen in the lower chamber. This provides the absorption and dissipation of the energy transmitted to the strut and controls the rate of vertical motion. Each strut contains the necessary seals to prevent the loss of nitrogen and hydraulic fluid.

A packing gland is installed at the open end of the outer cylinder to seal the sliding joint between the telescoping cylinders. A scraper also is installed in a groove in the upper jacket to keep the sliding surface of the lower cylinder free of dirt, mud, ice, snow, and other contaminants.

NOSE LANDING GEAR STRUT

The nose landing gear strut is identical in operation to the main landing gear strut, except for the addition of a metering pin at the orifice which, in effect, creates a variable orifice. The effective size of the orifice, and hence the restriction to fluid flow, varies with the amount of compression and extension of the strut. A taxi light, a nose wheel steering actuator, and a nose wheel centering device are installed on the nose gear strut. The taxi light and the nose wheel steering system are discussed in later sections of this manual.

NOSE WHEEL CENTERING DEVICE

The nose wheel centering device consists of a fixed cam attached to the stationary upper section of the strut and a follower arm and roller device attached to the scissors between the two sections of the strut.

As the weight of the airplane is removed from the nose gear, the weight of the gear plus the force of the nitrogen pressure causes the strut to extend. These extension forces also are transmitted through the scissors to the follower arm and roller assembly which tracks to the center of the cam and thereby moves the steerable portion of the nose gear to the centered position.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS LANDING GEAR NOSE LANDING GEAR

SA227‐ SERIES/FCOM/VTM

6.32.4

Figure 6.32‐2

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS LANDING GEAR SA227‐ SERIES/FCOM/VTM VARIABLE AUTHORITY NOSE WHEEL STEERING

6.32.5

A hydraulically powered, electrically controlled actuator is used for nose wheel steering. Controls for the system include a test switch, an arm switch, and a park button all installed on the left hand console. A nose wheel steering button is installed on the left hand power lever. Either the power lever button or the right speed lever micro switch will provide electrical power to the actuator.

For normal steering operations with the nose wheel steering switch armed and either the speed lever switch made or the power lever button depressed, the rudder pedals are moved to steer the airplane.

Steady illumination of the NOSE STEERING light indicates the system is armed and the direction of the aircraft should respond to rudder pedal deflection.

If more steering authority is required, the park button may be depressed. This increases the maximum nose wheel deflection from 10 degrees to 63 degrees left or right. An electrical delay prevents abrupt transition to or from the parking mode.

NOSE WHEEL STEEERING PANEL

Figure 6.32‐3

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

LANDING GEAR SA227‐ SERIES/FCOM/VTM 6.32.6 EMERGENCY EXTENSION OF LANDING GEAR

Both DC electrical power and hydraulic pressure (approximately 250 psi minimum) are required for normal extension of the landing gear. Electrical circuitry for landing gear control and position indication can be switched to either essential bus via one of the nine bus transfer switches located on the pilot’s console. Normally, the left essential bus is selected. If a failure of left essential bus power occurs, the circuitry should be switched to the right essential bus. Loss of electrical power from both essential buses or loss of hydraulic pressure will require emergency extension of the gear.

The landing gear emergency extension system includes provisions for manual release of the mechanical uplocks, manual repositioning of valves to bypass the gear selector valve, and a hydraulic hand pump.

Stand pipes in the hydraulic reservoir reserve approximately one quart of hydraulic fluid for hand pump operation if a loss of normal system hydraulic fluid occurs.

The EMERGENCY PROCEDURES section contains the procedures for emergency extension of the landing gear. When the emergency release lever, located on the cockpit floor to the left of the copilot’s seat, is moved counterclockwise to its stop (approximately 90°), cables release the mechanical uplock on each gear and reposition two gear bypass valves located underneath the forward side of the hydraulic reservoir. The repositioning of these two valves allows the fluid trapped in the “up” lines of the actuators used for normal retraction to bypass the gear selector valve and return to the reservoir. The gear then free falls. The gear weight plus the force of the airstream move the gear to the down and locked position.

After the gear has been allowed to free fall, hydraulic fluid via the hand pump is used to apply additional force. The hand pump, located on the cockpit floor adjacent to the pilot’s seat, is blocked by an emergency gear valve lever. When this valve lever is rotated approximately 90° counterclockwise, the hand pump bypass line is closed and the hand pump handle is free. The hand pump can then be actuated to provide hydraulic pressure to the down side of the auxiliary actuator at each landing gear.

A shuttle valve is installed between an engine driven pump pressure line and an emergency hand pump pressure line. The valve is moved by hydraulic pressure to direct the higher of the two pressures via electrical signal from a pressure transducer to the hydraulic pressure gauge located on the copilot’s instrument panel. If normal hydraulic pressure has been lost, the hydraulic pressure gauge will indicate hand pump pressure.

PARKING BRAKE

To set the parking brake, push the button in the center of the knob and pull the parking brake control to its fully extended (aft) position. Release the button and hold the knob fully out while applying pressure to either set of brake pedals. Release the force on the brake pedals and then release the parking brake knob (which will stay in its fully extended position). To release the parking brake, apply pressure to the brake pedals while pushing the parking brake control full forward. Brake pressure will release when the brake pedals are released.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS LANDING GEAR

SA227‐ SERIES/FCOM/VTM

6.32.7

PILOT’S OPERATING TIPS

VARIABLE AUTHORITY NOSE WHEEL STEERING TESTS

When the variable authority nose wheel steering test switch is held to either the left or right position, a strong steering signal is sent to the actuator to turn in that direction. The fault detection circuit immediately senses this signal as a fault and cancels the signal, stops the steering servo, and causes the nose steering light on the annunciator panel to blink. The nose wheel steering will remain disabled and the annunciator light will blink until the test switch is released to its neutral position.

If nose wheel steering is tested while holding the park mode button down and the park mode button is released before the test switch is released, the nose wheel steering is likely to remain disabled until the park mode button is depressed again and the rudder pedals are returned to the position they were when the test was begun. Another way to clear such a continuing fault is to turn the nose wheel steering switch off, align the rudder pedals with the nose wheel, and turn the nose wheel steering switch on again.

If the nose wheel steering system is tested while taxiing at relatively high speed, the fault introduced will cause the airplane to begin a turn at a rate which might be objectionable to passengers. Therefore, for passenger comfort, it is recommended that the nose wheel steering test be accomplished while taxiing slowly.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS LANDING GEAR

SA227‐ SERIES/FCOM/VTM

INTENTIONALLY LEFT BLANK

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

6.32.8