The function of the flap system is to move the flap control surface to the position that is set by the pilot. The flap system uses a hydraulic flap power unit to supply the necessary torque to the flap actuators. A system of flexible and hard shafts connects the flap power unit (FPU) to the actuators. The flap system is controlled by the flap control and indication system. The left and right hydraulic systems are used to energize the flap system.

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The FPU torque is transmitted to the left and right adapter gearboxes by two flexible shafts. Each flexible shaft is made of a Teflon steel-braided outer-casing. The outer-casing has a Santoprene cover. The inner-core is made of carbon steel wire. The inner-core connects to end-fittings made of steel that are corrosion resistant. The end-fittings have drive splines that connect to the FPU and to the adapter gearbox.

One end of the inner-core is fixed to the end-fitting. The other end is free to move axially. This lets movement between the inner-core and the outer-casing during installation. The end fittings have marks to show the fixed and free ends. A beryllium copper thrust-washer, found between the end fitting and the outer-casing, reacts to lateral loads and makes a seal.

O-rings seal the two ends of the outer-casing. Shrink tubing prevents the entry of hydraulic fluid and condensation. The fixed end of the flexible shaft is identified by a red warning label, found on the end-fitting. The label recommends not to twist or kink the shaft during installation. The flexible shaft has a minimum installation bend radius of 20 in (50.80 cm).

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There are three hard shafts installed in each wing. The hard shaft is a stainless steel tube that has a welded flange on each end. The hard shafts have universal joints which are attached to the flanges with four bolts and locknuts. Each universal joint has male splines on each end. The splines are made of corrosion resistant steel and are cadmium plated to prevent seizing. There are two interchangeable configurations for the No. 2 and No. 3 hard shafts.

Hard shafts transmit the torque from the adapter gearboxes to the inboard flap actuator. From the inboard flap actuator the torque is transmitted to the flap transmission brake (FTB) and then to the outboard flap actuator.

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There is an adapter gearbox installed in each wing. The adapter gearbox connects the flexible shaft to the hard shaft. The adapter gearbox decreases the speed of the flexible shafts from 2,000 to 870 rpm for the hard shaft. The adapter gearbox is attached to the aircraft structure with bolts through four adapter gearbox case flanges.

The adapter gearbox has two spur gears which have pairs of ball bearings for support. The gearbox is lubricated with MIL-H-5606 hydraulic fluid. The male input shaft and the female output shaft are sealed to prevent fluid leaks. The gearbox has a plug installed in its case to examine the fluid level and to fill the gearbox if necessary.

The same type of gearbox is used on the left and right wing. Two fill plugs are necessary because the installation of the gearbox on the right wing is opposite to the left. The plugs have a label to show which is to be used for the left or right installation. The gearbox contains a male spline for the connection to the flexible shaft and a female spline for the connection to the hard shaft. A locking plate engages with a slot in the outer-casing of the flexible shaft to keep it in position.

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The flap control surfaces of each wing are operated by two flap actuators. The inboard actuator has a longer travel than the outboard actuator. The flap actuator is connected to the wing structure by a gimbal configuration that provides for movement in two planes. Also, the flap actuator connects to the roller carriage with a gimbal. The gimbals at each interface contain bushings.

The flap actuators are made of a head case, a drive-screw, and a nut. The head case contains spur gears that move the torque from the hard shaft to bevel gears. The bevel gears then turn the drive-screw. The drive-screw moves the nut along its travel, which then moves the roller carriages and the flap control surface. The head case is made from aluminum precision castings which are anodized on the external surfaces for corrosion protection.

The drive-screw and nut are made of low alloy stainless steel to give good corrosion resistant properties. The ball race and the nut are hardened to give good wear properties. These properties keep the maintenance of the drive-screw and nut to a minimum. A grease fitting in the nut will let the assembly be lubricated at the recommended intervals.

There are stops at each end of the drive-screw. This will stop the nut travel if it moves more than one screw pitch in each direction. Gear ratios are the same in the two actuators. The inboard flap-actuator drive-screw has a different pitch on the screw thread which lets the drive-screw travel be longer.

The flap actuator gears are lubricated with MIL-H-5606 hydraulic fluid. This fluid gives satisfactory lubrication through the operating temperature range of the unit. The head case is sealed with standard rotary shaft seals to prevent fluid leaks and the access of contamination. The flap actuator has a plug installed in its head case to examine the fluid level and to fill the actuator if necessary.

Each actuator contains an internal torque limiter to prevent a structure overload if there is a locked condition in the flap track and roller carriage. In operation, the torque limiter senses the load on the drive-screw output. At a set level (20 to 60% more than the maximum operating load) a mechanism disconnects the head case spur-gears from the drive-screw. The torque limiter can be set again by a flap selection in the opposite direction to that which caused the locked condition.

Position sensors of the dual resolver type, are installed on the outboard flap actuators only. The position sensor drive-shaft has a direct spline into the flap actuator and is attached with three bolts through a flange mounting.

One of the resolvers on each wing is used for position feedback for flap system malfunction and asymmetry conditions. By comparison of the left and right wing resolver positions, the flap control unit (FCU) monitors malfunctions in the drive line which result in the flap panel asymmetry.

The second resolver in each of the position sensors is used for a separate flap position indication to the EICAS through the FCU. Each position sensor has two electrical connectors. The connectors have different key configurations to prevent an incorrect connection to the aircraft wiring.

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The flap transmission brake (FTB) is installed on the wing trailing edge of each wing, between the flap actuators. The FTB transmits the FPU torque from the inboard flap actuator to the outboard flap actuator through the hard shafts. The function of the FTB is to prevent uncommanded movement of the flap control surface. The FTB also locks the flap system if there is a flap malfunction.

The FTB is made of the parts that follow:

• Main Supply Solenoid
• Alternate Supply Solenoid
• Spring Packs
• Friction Plate
• Release Pistons

Six spring packs which have equal space between them apply a compression force on the friction plate. Six spring packs are used to make sure that the FTB will operate although some of the spring packs are defective. When compressed, the friction plate prevent movement of the flap system.

The FTB is a duplex hydraulic pressure-off-brake. It is connected to the left and right hydraulic systems. The alternate supply solenoid is operated by the left hydraulic system and the main supply solenoid is operated by the right hydraulic system.

When the FTB is not pressurized, the flap system cannot move. When the main supply solenoid or alternate supply solenoid is energized, the release pistons are pressurized. The release pistons then release the compression force of the spring packs. The friction plates then have no load and can move freely which then will let the flap system operate.

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One flap control surface is installed on each wing trailing edge, between the inboard trailing edge and the aileron. The flap control surface is a fowler-type flap. It is installed on three flap tracks and is connected to the roller carriages. The flap control surface has the components that follow:

• Front Spar
• Rear spar
• Ribs
• Skin Panels
• Access Panels

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Three roller carriages are installed on the bottom side of each flap control surface. The inboard roller carriage is at WS121.50. The middle roller carriage is at WS202.75. The outboard roller carriage is at WS263.90. The roller carriages connect the flap control system to the flap support structures. Each roller carriage is installed on the flap tracks and the track support ribs.

The stop fittings on the flap tracks stop the roller carriage if it moves too much aft. This prevents the roller carriage to come off the flap track.

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The roller carriage rollers are installed on the roller carriages. The rollers let the roller carriage to move freely along the flap track. Each roller carriage has four main rollers and four side rollers. Each roller is the needle type bearing. The roller carriage rollers are lubricated through four grease nipples.

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The flap power unit (FPU) is installed at the top of the right main landing gear (MLG) bay area. The FPU has the parts that follow:

• Hydraulic Motor
• Gearbox
• Spool Shut-Off Valve (SSOV)
• Two Pilot Operated Check-Valves (POCV)s
• Electro-Hydraulic Servo Valve (EHSV)
• Pressure-Off Brake (POB)
• POB Solenoid Valve
• Main Supply Solenoid Valve
• Alternate Supply Solenoid Valve
• Pressure Transducer
• Accumulator
• Two Check Valves
• Two Filters

The hydraulic supply of 3,000 psi (20,684.27 kPa) used for the hydraulic motor is supplied from the left or right hydraulic system. The right hydraulic system pressure is used for the main supply and the left hydraulic system is used for the alternate supply. The supply can be set by the pilot through the HYDRAULIC control panel. The hydraulic motor speed is controlled by the FCU through the EHSV. The speed control makes sure that the flap control surface moves at the correct intervals, independently of load conditions.

If there is no command to move the flap control surface, the main supply line is closed by the spool shut-off valve. At the same time the alternative supply line is closed with a pilot-operated check valve. In this case, there is no pressure available at the EHSV and at the POB solenoid valve.

If there is a command for the flaps to move with the main hydraulic supply, the SSOV opens. This pressurizes the EHSV and the POB solenoid valve. If there is a command for the flaps to move with the alternate hydraulic supply, the POCVs for the supply and return lines open. This pressurizes the EHSV and the POB solenoid valve. The pressure transducer is not pressurized if the SSOV and the POCVs are in the closed position.

The hydraulic motor has a POB. The POB is controlled by the POB solenoid valve. To make sure the POB does not release in the case of a POB solenoid valve malfunction, hydraulic pressure is supplied to the POB solenoid valve from the SSOV and the POCVs. The POB can only be released by the FCU, if sufficient supply pressure is available.

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The FPU ecology bottle is installed at the bottom of the right main landing gear (MLG) bay area. It is connected to the FPU seal drain-port by a flexible silicon tube. If there is too much fluid in the FPU ecology bottle, it is sent overboard by a different flexible silicon tube. The FPU ecology bottle is isolated from the FPU. The FPU ecology bottle is transparent to see the level of liquid in the bottle.

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Three flap solenoid valves are installed on the FPU and two solenoid valves are installed on the FTB.

When there is an electrical current through the solenoid valve, hydraulic pressure goes to the pressure inlet. This lets hydraulic pressure go to the control port and go into the FPU or FTB. When there is no electrical current through the solenoid valve, hydraulic pressure will go from the control valve to the return line. Thus, when hydraulic pressure is not necessary for the FPU or FTB it is drained.

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The flap system is operated by the FPU, which is installed on the fuselage. The FPU hydraulic motor transmits power to the FPU gearbox. The FPU gearbox decreases the output speed to 2,000 rpm. This is the necessary speed for the flexible shaft part of the transmission system.

The main hydraulic supply for the FPU is from the right hydraulic system. For safety, the FPU is also connected to the left hydraulic system for an alternate hydraulic supply. This will make sure that the flaps can operate during an one engine operation condition. The hydraulic supply can be changed by the pilot when the ALTN FLAPS pushbutton annunciator (PBA) on the HYDRAULIC control panel is pushed. When the ALTN FLAPS PBA is pushed, the PBA lamp will come on and show the legend ON.

The output power is transmitted through a drive shaft system to flap actuators found in the wings. The transmission system has a flexible shaft for the first section and hard shafts with a FTB for the second section. The hard shafts' universal joints are used to align the hard shafts. The adapter gearbox decreases the speed and connects the flexible shaft to the hard shaft.

The flap system operates the flap control surfaces with two flap actuators on each wing. If at one of the flap actuators, the output load is more than the limit, then the torque in the related actuator will increase. This will cause the related torque limiters in the flap actuator to operate. After a locked condition occurs, the torque limiter can be set again. This is done by a change in the flap selection in the opposite direction to that which caused the locked condition.

Malfunctions in the transmission system will be sensed by the position sensors. In malfunction cases, the transmission system will be immediately stopped by the pressure-off brake in the FPU. The disconnected transmission system will be kept stopped by the FTB.

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The flap system has interfaces with the components/systems that follow:

• Stall Protection System
• Control and Indication System
• FLAP Lever
• Flap Control Unit (FCU)
• Flight-Compartment Control System
• Left and Right Hydraulic Systems
• Engine Indication and Crew Alerting System (EICAS)
• Flaps

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
-	FLEXIBLE SHAFT (LH)	ZONE(S) 731	27−52−01
-	FLEXIBLE SHAFT (RH)	ZONE(S) 741	27−52−01
-	INBOARD HARD SHAFT (LH)	ZONE(S) 571	27−52−05
-	INBOARD HARD SHAFT (RH)	ZONE(S) 671	27−52−05
-	MIDDLE HARD SHAFT (LH)	ZONE(S) 571	27−52−05
-	MIDDLE HARD SHAFT (RH)	ZONE(S) 671	27−52−05
-	OUTBOARD HARD SHAFT (LH)	ZONE(S) 571	27−52−05
-	OUTBOARD HARD SHAFT (RH)	ZONE(S) 671	27−52−05
-	ADAPTER GEARBOX (LH)	ZONE(S) 571	27−52−09
-	ADAPTER GEARBOX (RH)	ZONE(S) 671	27−52−09
-	INBOARD FLAP ACTUATOR (LH)	ZONE(S) 573	27−52−13
-	INBOARD FLAP ACTUATOR (RH)	ZONE(S) 673	27−52−13
-	OUTBOARD FLAP ACTUATOR (LH)	ZONE(S) 574	27−52−15
-	OUTBOARD FLAP ACTUATOR (RH)	ZONE(S) 674	27−52−15
A203	FLAP TRANSMISSION BRAKE (LH)	ZONE(S) 571	27−52−19
A204	FLAP TRANSMISSION BRAKE (RH)	ZONE(S) 671	27−52−19
A123	FLAP POWER UNIT (FPU)	ZONE(S) 184	27−52−33
-	FLAP POWER UNIT (FPU) ECOLOGY BOTTLE	ZONE(S) 184	27−52−35

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