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the APU generator is ready for operation.
STARTING - DESCRIPTION AND OPERATION
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1.
General
_______ The starter motor rotates and accelerates the rotor of the APU to 50 % (above 20,000 ft at 58%) of the APU's normal speed. You operate the starting system from the APU panel in the cockpit. The Electronic Control Box (ECB) 59KD controls the start sequence of the APU. Three consecutive start attempts are permitted without cooldown. After the third start attempt the starter motor must cool down for at least 60 minutes.
2.
Component Location
__________________
(Ref. Fig. 001)
-------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA | | | | DOOR | REF.
-------------------------------------------------------------------------------2KA START SWITCH 25VU 210 5KA START CONTACTOR 120VU 212 6KA FUSE - APU START SUPPLY 120VU 212 132AZ 8KA STARTER MOTOR 313 315AL/ 49-42-51
316AR 10KA BACKUP START CONTACTOR 120VU 212
3. System Description
__________________
The primary parts of the starting system are:
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the starter motor,
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the starter clutch module,
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the start contactor,
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the back-up start contactor,
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the ECB. When you operate the starting system the ECB energizes the start contactor (5KA) and the back-up start contactor (10KA). Thus the 28 V DC is supplied to the starter motor. The starter motor turns the APU main shaft through the starter clutch module and the gearbox. At 50% APU speed (above 20,000 ft at 58%) the ECB disengages the starter motor. The starter clutch module disengages mechanically when the self sustained APU speed is more than the starter motor speed. The timed acceleration logic of the ECB controls the APU acceleration during the APU start. The starter motor has a brush wear indicator to show if the brushes inside the motor are serviceable.
4. Power Supply
____________ The starting system gets the electrical power from the DC system of the aircraft. It supplies 28VDC from the BAT BUS 3PP through a fuse (6KA) and the start contactors to the starter motor (8KA).
R EFF : 001-049, 101-105, 107-107, 151-199, 49-42-00Page 1 201-210, Config-2 Aug 01/05
CES
Starting System - Component Location Figure 001 (SHEET 1)
R EFF : 001-049, 101-105, 107-107, 151-199, 49-42-00Page 2 201-210, Config-2 Aug 01/05
CES
Starting System - Component Location Figure 001 (SHEET 2)
R EFF : 001-049, 101-105, 107-107, 151-199, 49-42-00Page 3 201-210, Config-2 Aug 01/05
CES 5. Interface
_________
The starting system has an interface with:
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the DC Generation System (Ref. 24-30-00),
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the Control and Monitoring System (Ref. 49-61-00).
6. Component Description
_____________________
(Ref. Fig. 002)
A. Starter Motor 8KA The starter motor is a series-wound DC motor. A V-clamp attaches the starter motor to the accessory drive gearbox. The motor drive spline-shaft engages with the splined shaft of the starter clutch module. The motor is totally enclosed and has overspeed protection. The electrical terminals of the motor are insulated. The motor includes a brush wear indicator which you can see in a clear plastic cover. When the indicator is shown, the brushes are serviceable. When the indicator pin is not seen you have to replace the starter motor. To manually turn the APU, a square end is installed on the shaft of the starter motor. A cap is fitted to protect the drive shaft.
B. Starter Clutch Module Between the starter motor and the accessory drive gearbox there is a starter clutch which makes the mechanical connection. Bolts attach the starter clutch module to the accessory drive gearbox. The clutch module has an inner splined shaft and an outer starter gear, which has a hollow shaft. Between the two shafts are the spring loaded sprags.
(1)
When the starter motor begins to turn, the friction locks the sprags between the races of the splined shaft and the starter gear shaft. The starter motor drives the starter gear through the clutch module.
(2)
During the start, the sprags engage between the splined shaft and the starter gear. When the starter motor is de-energized the motor speed decreases. The starter gear shaft (now driven from the gearbox) turns with a higher speed than the splined shaft of the clutch module. The sprags then disengage.
C. Start Switch The START switch 2KA is a non latching ON/OFF pushbutton switch. A blue colored ON legend comes on when the APU is started. A green colored AVAIL legend comes on when the APU is ready to supply electrical power or pneumatic power to the aircraft systems.
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