The APU may be used as a pneumatic source up to:
Pulling up the APU fire warning switch:
In flight, if the APU is the only source of electrical power, all galley busses are automatically shed. If electrical load still exceeds design limits, both main busses automatically shed until the load is within design limits. On the ground, the APU attempts to carry a full electrical load. If an overload condition is sensed, the APU sheds galley busses first, and then both main busses until the load is within limits.
When the APU is started using battery power only, there is a normal indication on the electrical metering panel that the APU generator has come on line and is ready to be selected.
When the APU is started using battery power only, there is a NO indication on the electrical metering panel that the APU generator has come on line and is ready to be selected. Both the frequency and voltage readings are zero until the APU generator is placed on line.
The APU switch OFF position has an automatic shutdown delay of:
The APU may be used as an electrical and pneumatic source simultaneously up to:
During APU operation, fuel is automatically heated to prevent icing:
It is recommennded to operate the APU for _____ before using it as a bleed air source.
This one minute stabilization is recommended to extend the service life of the APU.
The APU starts, operates and can supply electrical power alone up to:
If the APU GEN OFF BUS light fails to illuminate by the end of the start cycle:
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APU operation requires the following:
When the APU is started using battery power only, there is no indication on the electrical metering panel that the APU generator has come on line and is ready to be selected. Both the frequency and voltage readings are zero until the APU generator is placed on line.
The APU OVERSPEED light illuminates when:
If light is illuminated when APU switch is placed to OFF, light extinguishes after 5 minutes (light is disarmed when the APU switch is in OFF position).
The APU can supply both transfer busses:
Of the four lights located on the APU control panel, which light will NOT cause an automatic shutdown of the APU when it illuminates?
Moving the battery switch to OFF automatically shuts down the APU.
! Because of power loss to the Electronic Control Unit (ECU)
The blue APU MAINT light means that:
Electrical power to start the APU comes from:
With AC power available, the starter generator uses AC power to start the APU. With no AC power, the starter generator uses battery power to start the APU.
APU cooling air:
The APU is capable of supplying bleed air for both air conditioning packs:
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If the APU is the only source of electrical power:
The APU Electronics Control Unit (ECU) provides:
The APU start cycle may take up to:
Automatic shutdown occurs in the event of EGT exceedance.
During the APU start cycle, the APU EGT indication may fluctuate from 0 deg.C to 1100 deg.C prior to normal EGT rise and the LOW OIL PRESSURE light may cycle on and off several times. These indications have no adverse effect on starting the APU. It is not necessary to monitor EGT during start.
