System Review PTM CH-06 (APU) Flashcards
APU Overview
Is a self-contained, gas turbine-powered, Honeywell Model RE100 (CS) unit. The APU supplies electrical and pneumatic power to the aircraft and is controlled by the APU panel located on the central pedestal and the APU GEN switch on the electrical panel.
APU Knob (ON)
When selected ON, it provides power to the APU system. It initiates an internal self-test and allows full control of the APU panel. During the self-test, the following indications will be seen:
APU FIRE light illuminates.
APU indication on EIS will momentarily display amber dashes then display green digits.
APU Knob (OFF)
In the OFF position, all power is removed from the APU. If running, the APU will shutdown.
APU Knob (START)
Closes the APU relay and provides electrical power for the APU start. The internal self-test must be complete prior to selecting “START”.
APU Test
Triggered automatically when the APU knob is moved to ON, and GARMIN systems are ready to test. The APU test is between 2 and 5 seconds long. While the test is running, the APU FIRE button is illuminated and the GARMIN system looks for inputs from the APU to check that it is OK. If the test is passed, the APU is allowed to start.
APU SYS FAIL
The APU SYS FAIL CAS message has a 10 second debounce. It will not appear until 10 seconds after moving the APU knob to ON if there is an internal failure of the APU.
It is permissible to attempt an APU start once the APU FIRE button has extinguished and the APU digits have posted on the EIS.
If there is an internal failure of the APU but the APU SYS FAIL CAS message has not posted due to debounce time, the APU will not start.
APU Start on the Ground
The APU can be started on the ground with battery power, a ground power unit, or engine generator power.
If battery power is used, the minimum voltage for start is sufficient when both left and right BATT V indications are green in the EIS ELECTRICAL window.
APU Start in the Air
In flight APU starts require the crew to place the BUS TIE button in the CLOSED position. This allows both batteries to participate in the APU start. The bus tie must be opened following start completion.
APU Generator Power
APU generator power can be used to assist in ground engine starts or supply power for the entire aircraft up to the APU maximum operational altitude.
Provided with a dedicated air-cooling exhaust pipe that increases the amount of air flow across the generator in flight for proper cooling.
APU Bleed Air
Bleed air from the APU is extracted from the compressor section and piped to the service air manifold and the Bleed Control Valve (BCV).
APU bleed air is available for environmental, pressurization, and service bleed systems only.
APU bleed air is not available for the anti-icing systems.
A printed circuit board and bleed air buttons control the BCV position to regulate air flow to the aircraft systems.
The BCV is closed for APU start and is either automatically or manually opened after APU start. Manual or automatic actuation is controlled by the APU BLEED AIR button position on the center pedestal.
Service air does not pass through the bleed control valve and is available anytime the APU is running.
If APU RPMs fall below a predetermined number or excessive exhaust gas temperature (EGT) is sensed, PCB logic automatically closes the bleed air control valve to an intermediate position.
APU Compartment
Is in the tailcone below the vertical stabilizer. The enclosure consists of a titanium fire box and debris shield, environmental protection for the APU installation, and protection for the rudder control cables.
APU Bleed Air Button
Selecting the APU BLEED AIR Button ON opens the APU Bleed Air Control Valve (BCV) to an intermediate position, approximately half open.
The BCV is closed during APU start, even if the button is selected ON, and automatically opens when the APU is ready to load.
Selecting OFF closes the BCV completely.
APU Exhaust
The end of the stinger provides exhaust for the APU and compartment ventilation
APU Intake
Is provided by a screen and a scoop located just below the rudder on the vertical stabilizer.
Accessory Gearbox
The accessory gearbox houses a starter-generator used to supply electrical power to the main electrical system.
APU Fire Protection
APU fire detection is accomplished with a loop assembly routed around the APU powerplant at strategic points. An excessive temperature sensed by the fire loop illuminates the red APU FIRE button located on the APU panel on the pedestal.
APU Fire Detection
Upon fire detection, the ECU initiates an abnormal shutdown of the APU and prevents restart.
APU Fire Button
Located below the APU knob. If an excessively high temperature is sensed by the fire-detection system in the APU compartment, the light illuminates and the APU automatically shuts down.
Pressing the APU FIRE button discharges the baggage/APU fire bottle in the tailcone into the APU compartment.
If the button is not pressed within 8 seconds after illumination, the baggage/APU fire bottle is discharged automatically.
APU Fire Extinguishing
Fire extinguishing of the APU is accomplished with a single halon-filled bottle in the tailcone. The bottle is shared with the baggage fire protection system.
APU Oil Reservoir
APU gearbox also functions as an oil reservoir that can use the same type of oil as the engines. Oil is sprayed on the compressor shaft by an oil pump and returned to the reservoir by scavenge pumps.
APU Temperature and Pressure Monitoring
The ECU monitors the oil temperature and pressure. If the oil temperature becomes excessive or the oil pressure becomes too low, the ECU shuts down the APU and the APU SYS FAIL CAS message is displayed. Oil bypass and chip collection are checked during inspections by maintenance.
APU Oil Lever Sensor
An APU oil level sensor checks oil quantity when the APU is requested ON. If the level is low, the APU OIL LEVEL LOW CAS message displays
Engine Control Unit
The ECU in the tailcone is a fully automatic digital unit that communicates with other aircraft systems. Output commands are sent to maintain safe operation and provide for automatic shutdown if required. The ECU controls all aspects of the APU operation, both normal and abnormal from start to shutdown.
Starter Generator
The APU starter-generator is on the accessory gearbox and is air-cooled.
The starter-generator has an internal fan that circulates air for cooling on the ground. The internal fan and ram air provide cooling in flight.
The starter-generator is interchangeable with the engine generator. The generator is rated at 28 VDC, limited to 275 amps.
The generator can temporarily exceed the continuous rating and provide up to 450 amps when assisting an engine start.
APU Generator Control
The APU generator is controlled with the APU GEN Switch on the ELECTRICAL control panel.
Selecting the APU GEN switch to the ON position closes the APU generator relay to power the left emergency bus.
The OFF position commands the GCU to open the APU relay and place the generator off line. Selecting the APU GEN RESET position momentarily attempts to regain generator power after an uncommanded failure.
APU Fuel Control Unit
The fuel control unit (FCU) attached to the APU filters the fuel, boosts the pressure, and regulates it through a torque motor metering valve. Any change in rpm is sensed by the ECU and sends a signal to the torque metering valve to increase or decrease the fuel flow to maintain rpm at 100%.
APU Fuel Shutoff Solenoid Valve
Fuel exiting the FCU passes through the APU fuel shutoff solenoid valve before reaching the primary and secondary fuel manifolds and six fuel nozzles for combustion. The fuel shutoff solenoid opens during start at 5% rpm and remains open until the ECU closes it during normal or abnormal shutdown.
APU RPM %
Provided by the ECU for display.
APU EGT °C
Provided by a thermocouple extending into the exhaust gas stream. The ECU uses this temperature for fuel scheduling, controlling the bleed-air control valve, and automatic shutdown due to overtemperature.
APU A
APU amp load.
APU V
Voltage is indicated when the APU is operating even if the generator is selected OFF. The numbers represent voltage available for use.
APU EIS L
TRU and APU share the same display location on the EIS. APU amperage and voltage information will overwrite TRU information.
APU Fuel Supply
Fuel is supplied to the APU from the right-wing fuel tank. The R BOOST PUMP is used, or if motive flow is available the electric fuel boost pump is not required.
Crossfeed from the opposite tank is possible.
A DC-powered electric motor valve opens when the APU knob is positioned to ON. This allows fuel from the wing tank to pass through the APU firewall to the APU. The valve closes when the APU knob is positioned to OFF, the APU EMERGENCY SHUTOFF button is pressed in the tailcone compartment, or the ECU commands it closed.
