APU

Question 1

APU Accessory Gearbox

Answer 1

Provides mounting pad for hydraulic starter and output driver for the APU fuel assembly, oil pump and air-cooled ac generator

Self-contained lubrication system

Question 2

Fuel Consumption

Answer 2

150 lbs/hr

Question 3

In Air Start

Answer 3

WARNING APU does not incorporate a compressor or turbine or wheel containment device. An uncontained APU failure may result in injury to ground personnel and/or damage to flight critical components including the tail rotor drive shaft

Question 4

Prime/Boost Pump

Answer 4

Used to prime the engine or APU fuel lines and provides fuel under pressure to the APU during starting and operations at altitudes above 8,000ft

Question 5

Hydraulic Accumulator

Answer 5

Provides pressure for driving APU starter

Min pressure required for starting APU is approximately 2,650psi

Can recharge by hand pump or backup hydraulic pump

Question 6

APU Control

Answer 6

ON opens APU airframe fuel shutoff valve and sends a start signal to the APU Electronic Sequence Unit (ESU) or Digital ESU (DESU)

OFF closes valve

Question 7

ESU/DESU

Answer 7

Controls and monitors APU

Automatically shuts down APU if start sequence fails or a monitored parameter is exceeded during operation (except APU OIL TEMP HI)

To maintain BIT codes, need dc power and APU CONTR switch to stay in ON position

Turbomach/Sundstrand has added capability to control APU overtemperatures by regulating main fuel valve and start bypass valve

Question 8

Start System

Answer 8

FUEL PUMP switch in APU BOOST: pressurized fuel from right cell

APU CONTR ON: initiates start sequence

ESU/DESU sends signal to open APU start valve, releasing hydraulic accumulator charge; fuel control allows starting in all ambient conditions and maintaining constant speed while running

APU GENERATOR to ON provides electrical power

Question 9

Start System (Manual)

Answer 9

FUEL PUMP switch in APU BOOST: pressurized fuel from right cell

APU CONTR ON: initiates start sequence

ESU/DESU sends signal to open APU start valve, releasing hydraulic accumulator charge; fuel control allows starting in all ambient conditions and maintaining constant speed while running

APU GENERATOR to ON provides electrical power

Manual start (if APU didn’t start and APU ACCUM LOW not illuminated) by simultaneously moving APU CONTR switch to ON and actuating the manual START/OVERRIDE lever on accumulator manifold