The function of the elevators is to give the pilot and copilot control of the aircraft about the lateral axis during flight. Forward and aft movement of the flight-crew control columns causes the two elevator control surfaces to move. The elevators, which are attached to the rear spar of the horizontal stabilizer, are not connected to each other.

The flight crew inputs to the elevator control circuit are through two control columns. The pilot and copilot control columns are connected together through a torque tube and they usually move as one unit. Control rods, quadrants, cables, and a torque tube transmit the pilot commands to four hydraulic power control units (PCUs) in the horizontal stabilizer. Two PCUs operate each elevator. There is a pitch disconnect mechanism which isolates the pilot's elevator control circuit from the copilot's if the controls do not move freely. If a series of defective components causes the available hydraulic pressure to decrease to zero, the flight crew can control the elevators mechanically.

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The pilot's and copilot's control columns are connected laterally by two torque tubes which have the same axis. These torque tubes attach to a pitch disconnect mechanism at the center of the aircraft.

The disconnect mechanism has an inner shaft and an outer housing with two roller bearings to keep them apart. The two coaxial halves have flanges which connect to the left and right torque tubes.

A plunger with a roller at one end is attached to the outer housing and it keeps the two torque tubes aligned axially. The plunger, which the flight crew can operate, usually stays with its roller in the engaged position in a recess in the outer shaft. A cable circuit connects the plunger to a PITCH DISC handle in the center pedestal.

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The PITCH DISC handle is found on the left side of the center pedestal, adjacent to the pilot's seat. When not in operation, it is pushed into a recess in the center pedestal. The handle attaches to a cable which goes down vertically to a pulley adjacent to the pitch disconnect mechanism. The routing of the cable is then across the aircraft to the right of the disconnect mechanism where it connects to a bell crank. A second cable connects the other end of the bell crank to the plunger of the pitch disconnect mechanism.

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There are four PCUs installed in the horizontal stabilizer, two of which are connected to each elevator. The left hydraulic system energizes the two inboard PCUs, and the right hydraulic system energizes the two outboard PCUs.

The usual hydraulic pressure is 3,000 psi (20,684 kPa). The PCUs are adjusted to keep their output force differences to a minimum on each elevator control surface. If hydraulic pressure is not available in flight, the PCUs work as rigid control rods and the flight crew can move the elevators manually.

The elevator system uses the PCUs on each elevator surface as a gust lock to give ground protection when the hydraulic systems are not energized.

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Two elevator-surface position sensors are rotary variable differential transformers (RVDT) installed in the horizontal stabilizer, one for each surface. For the left elevator, the sensor is installed aft of the inboard PCU. For the right elevator, the sensor is installed aft of the outboard PCU. They are each connected to their related elevators by two links. When the angle of the elevators change, the sensors transmit position data to the data concentrator unit (DCU). This data is then shown on the EICAS flight controls synoptic page.

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There are two control columns in the flight compartment. They are found between the instrument panel and the pilot's and the copilot's seats. The control columns are mechanical levers which are used to transmit pilot/copilot inputs to the elevator controls.

A balance spring is installed on each control column between the control column and a bracket which is attached to the structure. The function of the control column balance springs is to supply a static mass balance to the elevator system. Thus, the balance springs supply a equal and balanced breakout property when the control column is pushed or pulled.

A bob-weight is installed on the forward side of each control column. These weights give more column load during pitch operations to add simulated force to the elevator pitch-feel system.

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A position sensor is installed at the outboard ends of the control column torque tubes. Two short links connect each sensor to the torque tubes. Movement of the torque tubes causes the sensors to turn and transmit control column position data to the flight data recorder only.

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There are two elevator control surfaces which are made of light alloy and composite materials. Each elevator has three hinges which attach it to the rear spar of the horizontal stabilizer. The two PCUs attach to positions on each side of the inboard hinge, near the lower edge of the hinge cutout. Access panels around the hinge points give access during installation and removal of the elevators. There are also some small inspection panels in the elevator lower surfaces.

At the outboard end of each elevator there is a horn balance structure which extends in front of the hinges. These structures contain 9 lb (4 kg) of lead which balances the mass of each elevator. The usual maximum range of travel of the elevators is from up 24 degrees to down 18 degrees. You can give the elevator surfaces 1.5 degrees of overtravel in each direction if you adjust the primary stops at the PCU input torque-tube. (If you do this, the PCUs stop at their internal limits.)

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The two pitch force sensors have the primary function of rigid rods. They are installed between the bottom of each control column and the forward quadrants. The other function of these sensors is to supply data on the force in the elevator control circuit to the flight data recorder.

The gain changer mechanism is installed between two pitch control rods in the vertical stabilizer. The pilot's elevator control input and the output from the pitch feel simulator are connected at one end of the lever mechanism. The lever has a pivot hole at its center through which a bolt attaches the mechanism to the structure. At the opposite end of the lever there are two short, connected links which attach the lever to a shear-out rod. A weight attached to one of the short links makes sure that the mechanism moves to a neutral position if hydraulic pressure is not available.

When the elevators are at or near their neutral position, the pilot must make large control inputs for a given elevator angle change. This makes the controls less sensitive around the neutral position. The gain changer mechanism makes sure that the necessary movement of the input controls becomes less when the elevator moves away from the neutral position.

The shear-out rod connects to the gain changer output at its bottom end and to an idler link at its top end. During usual operation the shear-out rod has the function of a rigid control rod. The rod has two coaxial, telescopic parts attached together with a shear pin. The function of this pin is to break when the load on the rod becomes too much. This can occur when the hydraulic pressure to the PCUs is not available and the pilot moves the elevator controls manually. When this occurs the shear-out rod expands and compresses a small distance, which decreases the total force on the controls downstream of the rod.

 

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Two centering spring cartridges attach to bell cranks in the left and right elevator control circuits at the top of the vertical stabilizer. The other ends of the spring cartridges attach to points on the structure. Each spring cartridge has a telescopic piston which moves in a cylinder. A shear pin is installed in the piston rod to connect the inner and outer parts of the rod.

If a control rod in the vertical stabilizer becomes disconnected in flight, the elevator PCUs can receive an unwanted input force. Two springs in the centering spring cartridge try to keep the piston in a neutral position. The result is that the elevator PCUs also keep the elevator in a neutral position that side of the aircraft. If a centering spring piston does not move freely in its cylinder, the control force input can break the shear pin in the piston rod. The result is that the pilot continues to have a full range of movement of the applicable elevator.

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An elevator entering mechanism is installed on the outboard end of the PCU inlet torque tubes. The elevator centering mechanism has the components that follow:

• A cam attached to the torque tube
• A roller attached to a main lever
• Two tension springs
• A lever support

The elevator centering mechanism is a device which has a force which is felt in one direction by the PCU torque tube. In the other direction a force is felt by the extension springs in the mechanism. The cam and roller are free of these two forces. Thus, if the linkage has a disconnect between the idlers and the elevator centering mechanism the elevator will center.

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The pilot and copilot inputs to the elevator circuit are by two control columns which are usually connected to each other through a torque tube. Rods connect the control columns to the left and right forward quadrants. These quadrants operate two sets of cables which go below the passenger compartment floor and through the rear pressure bulkhead. In the area of the rear fuselage adjacent to the engine installations, the cables go in different directions. This is for the safety of the elevator controls if a part of the engine rotor breaks at high speed and goes through the fuselage. The cables then connect to the rear quadrants at the bottom of the vertical stabilizer.

A third quadrant attaches to the same axis as the rear quadrants. The cables on this quadrant connect to the elevator servo which is installed in the rear fuselage.

Note:
The elevator servo is a component in the autopilot system. For more data, refer to the Automatic Flight-Control System.

The rear quadrants transmit the pilot inputs through the vertical stabilizer to a gain changer mechanism and a pitch feel simulator. A series of control rods, levers, and torque tubes then transmit the pilot inputs to two elevator power-control units (PCUs) on each control surface. The torque tubes in the horizontal stabilizer give synchronized inputs to the two PCUs on each elevator.

When the two elevator control circuits move freely, the pilot's and the copilot's control columns move as one unit. If one of the control circuits cannot move freely, the flight crew can quickly disconnect the two halves of the torque tube. One of the pilots can pull up and turn the PITCH DISC handle to lock it in the disconnected position.

After they are disconnected, the two control columns are free to move independently in relation to each other. This gives the pilot sufficient, but decreased, pitch control of the aircraft through the elevator which is connected to the free circuit. If the left elevator circuit is defective, autopilot control of the elevators will not be possible.

If the PITCH DISC handle is turned and released, the plunger of the pitch disconnect mechanism can go back into its recess. If the two halves of the elevator torque tube are not initially aligned together, a small movement of one of the control columns is necessary. This is sufficient to let the plunger go back into the locked position with the aid of a spring.

The force which the pitch feel simulator transmits back to the pilot is in proportion to the force necessary for the PCUs to move the elevators. This force changes with a change in airspeed and with a change in the angle of attack of the horizontal stabilizer. When hydraulic pressure is not available to the elevator PCUs, the pilot can continue to move the elevators manually. Because the input force necessary at this time increases, the hydraulic lockout rods extend and set the pitch feel simulator into a new datum position. This decreases the force which the pitch feel simulator applies to the elevator input controls.

The elevator position indication is shown on the FLIGHT CONTROLS synoptic display on the EICAS status page. This display shows the left and right elevator movements in the up or down positions on scales with pointers. The scales has the legends ELEVATOR and marks at the full up, the full down and the neutral positions.

The PITCH DISCONNECT warning message will show when a pitch disconnect has occurred when the aircraft is in take-off configuration.

The ELEVATOR SPLIT caution message will show when there is a difference of 32.5 degrees between LH and the RH elevator surface-position and the aircraft is on ground.

The PITCH DISCONNECT status message will show when a pitch disconnect has occurred when the aircraft is not in take-off configuration.

The EICAS messages that follow are related to the elevator control system:

EICAS MESSAGE(S)	LEVEL (COLOR)
PITCH DISCONNECT	WARNING (red)
ELEVATOR SPLIT	CAUTION (amber)
PITCH DISCONNECT	STATUS (white)

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
-	PITCH DISCONNECT MECHANISM	ZONE(S) 141	27−31−01
-	PITCH DISC HANDLE	ZONE(S) 211	27−31−01
-	ELEVATOR POWER-CONTROL UNIT (PCU) (LH)	ZONE(S) 351	27−31−09
-	ELEVATOR POWER-CONTROL UNIT (PCU) (RH)	ZONE(S) 361	27−31−09
MPE51	SURFACE POSITION SENSOR (LH)	ZONE(S) 351	27−31−13
MPE52	SURFACE POSITION SENSOR (RH)	ZONE(S) 361	27−31−13
MPE53	CONTROL-COLUMN POSITION SENSOR (LH)	ZONE(S) 141	27−31−15
MPE54	CONTROL-COLUMN POSITION SENSOR (RH)	ZONE(S) 142	27−31−15
-	ELEVATOR CONTROL SURFACE (LH)	ZONE(S) 352	27−31−17
-	ELEVATOR CONTROL SURFACE (RH)	ZONE(S) 362	27−31−17
MT109	PITCH FORCE SENSOR (LH)	ZONE(S) 141	27−31−21
MT110	PITCH FORCE SENSOR (RH)	ZONE(S) 142	27−31−21
-	GAIN CHANGER MECHANISM	ZONE(S) 341	27−31−25
-	SHEAR-OUT ROD	ZONE(S) 341	27−31−31
-	CONTROL-COLUMN (LH)	ZONE(S) 211	27−31−33
-	CONTROL-COLUMN (RH)	ZONE(S) 212	27−31−33

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