APU

Question 1

Fuel to start and operate the APU comes from ?

Answer 1

The left side manifold when the AC fuel pumps are operating.

Question 2

The APU fuel boost pump is (blank) operated to ensure ?

Answer 2

DC operated to ensure positive fuel pressure to the APU fuel control unit

Question 3

When does the APU fuel boost pump operate ?

Answer 3

It operates during start and operation automatically when the APU fuel control unit senses low fuel pressure

Question 4

When does the APU fuel boost pump turn off

Answer 4

The APU automatically shuts off when the an AC fuel pump pressurizes the fuel manifold

Question 5

If the AC and DC fuel pump are not operating how does the APU get fuel

Answer 5

If the AC and DC fuel pump are not operating fuel is suction fed from the no.1 tank.

Question 6

APU engine air routes from where?

Answer 6

An automatically operated air inlet door located on the right side of the fuselage.

Question 7

How is the APU cooled?

Answer 7

Air for APU cooling enters through a cooling air inlet above the APU exhaust outlet. This air circulates through the APU compartment, passes through the oil cooler and vents through the exhaust outlet.

Question 8

Requirements to start the APU

Answer 8

• APU fire switch on the overheat/fire panel must be In
• APU fire control handle on the APU ground control panel must be in
• Battery switch must be on
• Electrically power from the #1 AC transfer bus or the battery bus is used to start the APU

Question 9

APU start sequence

Answer 9

APU switch to start > initiates opening of the air inlet door > When APU inlet door full open start sequence begins > Once APU reaches proper speed, ignition / fuel provided > When the APU is ready to accept bleed air / electrical load the APU GEN OFF BUS light illuminates

Question 10

How long can it take for the APU to start ?

Answer 10

120 seconds

Question 11

automatic shutdown protection of the APU occurs if ?

Answer 11

If EGT is exceeded, overspeed conditions, low oil pressure, high oil temp, APU fire, fuel control unit failure

Question 12

Moving the APU switch to OFF begins what sequence for shutdown

Answer 12

trips the APU gen > closes the bleed air valve > extinguishes the APU GEN OFF BUS light > shutdown occurs after 60 seconds > when the APU speed decreases the fuel valve and inlet door close > if the fuel valve does not close the FAULT light will illuminate