APU Start
The automatic start sequence begins by moving the APU switch momentarily to START.
This initiates opening of the air inlet door. When the APU inlet door reaches the full open
position the start sequence begins. After the APU reaches the proper speed, ignition and
fuel are provided. When the APU is ready to accept a bleed air or electrical load the APU
GEN OFF BUS light illuminates.
Note: 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.
Note: During the APU start cycle, the APU EGT indication may fluctuate from 0º to 1100º 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.
If the APU does not reach the proper speed with the proper acceleration rate within the time
limit of the starter, the start cycle automatically terminates. The start cycle may take as long
as 120 seconds. Automatic shutdown occurs in the event of EGT exceedance.
If the start fails or the APU GEN OFF BUS light fails to illuminate by the end of the start
cycle, a system failure has occurred and the FAULT light illuminates.
Operate the APU for one full minute before using it as a bleed air source. This one minute
stabilization is recommended to extend the service life of the APU.
