737 MAX Flight Crew Operations Manual
Engines, APU -
APU System Description
7.30.4
MN-FLT-OH-201
The ECU automatically controls APU speed through the electronic fuel control. If
speed or EGT exceed acceptable levels with the APU providing electrical load
only, some electrical load is shed. When electrical load and air extraction raise the
EGT above acceptable levels during engine starting, electrical load shedding
occurs prior to reducing bleed air. When electrical load and air extraction raise the
EGT above acceptable levels other than during engine starting, the inlet guide
vanes move toward a closed position, reducing bleed air extraction while
maintaining electrical load.
APU Automatic Load Shedding
In flight, if the APU is the only source of electrical power, all galley buses and
main buses are automatically shed. If electrical load still exceeds design limits,
both IFE buses are also automatically shed. On the ground, the APU attempts to
carry a full electrical load. If an overload condition is sensed, the APU sheds
galley buses and main buses until the load is within limits. Manual restoration of
galley and main bus power can be attempted by moving the CAB/UTIL Power
Switch to OFF, then back ON.
March 1, 2021
