APU SYSTEM LINE MAINTENANCE
SYSTEM OVERVIEW
The Auxiliary Power Unit (APU) is a constant speed gas turbine engine.
It is located in the unpressurized tail cone. The APU is a self-contained
unit, which enables the aircraft to be independent of external pneumatic
and electrical power sources.
The constant-speed gas turbine engine drives the accessory gearbox and
a load compressor. The APU provides:
- electrical power for the aircraft systems,
- bleed air for engine starting (MES), air conditioning (ECS) and wing
anti ice testing on ground (not GTCP 36-300),
- bleed air for air conditioning and pressurization in flight until the
specified manufacturer limit.
The APU is designed to operate throughout the entire flight envelope.
Electrical power is available whenever the APU operates, but bleed air
is shut off above the specified manufacturer limit.
The APU has an air intake flap. The intake flap is open when the APU
master switch is selected ON and closes when the master switch is selected
OFF. When open, it provides air to the APU inlet for combustion and
pneumatic supply
oil servicing is accomplished on an "as-needed" basis or after
scheduled oil quantity checks. The oil indicating system shows if the
oil quantity is sufficient or if an oil servicing is necessary.
The oil level information is displayed on the EIS and the Multipurpose
Control & Display Units (MCDUs) in the cockpit on:
- the APU page on the lower ECAM display unit (LOW OIL LEVEL
advisory),
- the APU SERVICE DATA page on the MCDU, indicating APU
OIL Level O.K. or LOW.
NOTE: Note: The advisory appears on the ECAM APU page when
the oil level has reached the ADD mark on the APU oil tank.
Airbus recommends servicing the APU oil at the next daily
maintenance when the LOW OIL LEVEL message comes on. With
no oil leakage, sufficient oil is available to allow a further 10 hours
of APU operation.
Prior to servicing, shut down the APU and open the APU cowl doors.
Make sure to use the operator approved oil for servicing (operators
may select from the approved list). The oil may be serviced by the
gravity (most common) or pressure fill procedure (optional).
Gravity procedure:
- Open the lock and slowly loosen the oil filler cap to release remaining
pressure from the oil reservoir,
- Check sight glass for level,
- Slowly add oil until the level is at the FULL mark on the sight glass.
Pressure fill procedure:
- Check sight glass for level,
- Connect pressure and overfill lines to APU gearbox,
- Slowly pump oil into the gearbox until the level is at the FULL mark
on the sight glass
APU COWL DOOR OPENING & CLOSING
The APU cowl doors are secured with three quick-release fasteners
and four shoot bolts. The quick-release fasteners secure the doors
together and the shoot bolts secure the doors to the aircraft structure.
Procedure to open the doors:
- Release the quick-release fasteners,
- Hold the LH door and release the latches of the 2 shoot bolts,
- Open the door and secure it with the telescopic strut,
- Hold the RH door and release the latches of the 2 shoot bolts,
- Open the door and use the control handle to secure the door over
center.
The doors are closed opposite from the opening sequence. The RH
door is closed and secured first.
MEL/DEACTIVATION
In case of an APU inlet actuator failure, the APU may be dispatched per
MEL with the inlet OPEN or CLOSED. The APU will only be operational
with the inlet deactivated OPEN (for a maximum of 10 days).
The air inlet actuator is equipped with a manual drive. In case of failure
the manual drive may be used to move the inlet to the required position
prior to deactivation. There are 2 different actuators that may be installed.
One requires 47 turns of the manual drive for one full travel of the inlet.
The other requires 87 turns. Access to the actuator is through an access
door near the APU inlet on the right hand side of the fuselage.
Deactivation procedure:
- get access to the actuator,
- disconnect the actuator electrical connector from the fixed connector
on the frame and install a blanking cap,
- use the manual drive to move the inlet to the required position. Use a
torque wrench to avoid damaging the actuator.
If the inlet is deactivated CLOSED, no further action is needed other than
to placard the APU inoperative. If the inlet is deactivated OPEN, the
following procedure has to be accomplished.
When the inlet is in the OPEN position, a jumper lead needs to be installed
to close the circuit and allow the APU to start. Make a dummy connector
and paint it red for easy identification.
MAINTENANCE TIPS
The APU fuel supply line is equipped with a drain and vent valve which
enables the line to be purged of air after maintenance. The drain valve is
located in the APU compartment in the fuel supply line to the fuel control.
A switch labeled FUEL VENT PUSH is installed on the APU
compartment forward firewall to allow maintenance to operate the APU
fuel pump and purge the fuel line from the APU compartment. This switch
allows the APU pump to operate and the APU Low Pressure fuel valve
to open without the APU Master Switch ON.
A drain valve adapter tool is connected to the drain valve.
On the front firewall of the APU compartment:
- Push and hold the FUEL VENT pushbutton switch. At the APU fuel
vent and drain valve, a continuous flow of fuel indicates that the APU
fuel pump is operating and the line is purged,
- Release the FUEL VENT pushbutton switch. The flow of fuel stops
when the APU fuel pump stops running,
- Disconnect the adapter tool.
If it is necessary to operate the APU for maintenance with the cowls
open, be sure to:
- Make sure the doors are secured in the Open position,
- Be aware of suction at inlet. Small items could be ingested,
- Make sure that proper fire-fighting equipment is available.
ENVIRONMENTAL PRECAUTIONS
Do not discharge products such as oil, fuel, solvent, lubricant either in
trash bins, soil or into the water network (drains, gutters, rain water, waste
water, etc...).
Sort waste fluids and use specific waste disposal containers.
Each product must be stored in an appropriate and specific cabinet or
room such as a fire-resistant and sealed cupboard.
Avoid use of the APU if APU BLEED air is not necessary. Turn-off
unused ground service equipment (GPU, Air conditioning cart, etc...) if
no work is being done or nobody is present on the aircraft.
Thankyou.....
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