CHAPTER 49 Flashcards
What is the purpose of the APU drain tank?
A drain system prevents the collection of fluids in the Auxiliary Power
Unit (APU) system and compartment. For venting and evacuation the drain tank is connected to the drain mast. Airflow across the drain mast creates a vacuum in the drain line. The suction effect produced at 200 kts, is sufficient to remove the contents of the drain tank.
With the APU running at 100% and the bleed pushbutton on how is the bleed air supplied to the aircraft from the APU?
When the APU Bleed P/B is pushed, the blue ON light in the P/B comes on and a signal is sent to the two BMCs and to the ECB to open the Bleed Control Valve (BCV).
How is Bleed air controlled from the APU?
To make sure that a pressure build-up occurs in the Aircraft Bleed supply duct, the ECB first commands the Bleed Control Valve (BCV) to the exhaust duct closed position and then modulates the BCV to prevent surge conditions. The BCV uses an LVDT for position feedback transmission to the ECB.
How does the APU protect against over temperature?
The APU guards against APU over temperature by controlling the Inlet Guide Vane (IGV) position to closed. Thus, the pneumatic load is first reduced to give priority to the electrical load.
How is the APU fuel system controlled?
The ECB controls the fuel system with several parameters. During
on-speed operation, the ECB uses APU speed, Exhaust Gas
Temperature (EGT) and aircraft demand signals.
How does the APU ECB control engine start?
During start, it uses speed, EGT, air inlet pressure and temperature sensors (P2 and T2). The ECB operates the fuel metering valve, the flow divider solenoid valve and the 3-way shut-off solenoid valve.
The ECB gives protection to the APU which oil parameters will cause the ECB starts an automatic shutdown?
The ECB gives protection to the APU if there is an oil system malfunction. The ECB monitors oil pressure and oil temperature. If
one of the oil parameters is out of limit, the ECB starts an automatic
APU shutdown without time delay if the gearbox high oil temp 162.78°C (325°F) or oil low pressure below 33 psi.
What is the main function of the APU cool down cycle and how is this achieved?
When the MASTER SW OFF, is pressed the pneumatic load is removed by moving the IGVs to closed, the bleed control valve positioned to discharge, the AC generator may still be loaded, then the engine goes into a 120 s cool down cycles. This function runs the APU at a low stabilized temperature before normal shutdown.
