Loss of ALL AC power includes APU
No. In the context of the FAA AD, the APU is not considered, as presumably the APU may not be operating at the time of the GCU failures (see below for exact wording).
The AD does NOT mean integer overflow in one GCU will shutdown the other three GCUs plus the APU as you seem to think. That is simply wrong!
The 787 has
six generators: 2 per engine (4 total) plus 2 more on the APU. The FAA statement makes clear that the issue affects the
four GCUs related to the engine, not any GCUs related to the APU.
Read the following sections from the FAA AD carefully:
The software counter internal to the generator control units (GCUs) will overflow after 248 days of continuous power, causing that GCU to go into failsafe mode.
Translation: overflow in one GCU unit only causes THAT one unit to go into failsafe mode. FAA wrote "
that unit", not "
all units".
If the four main GCUs (associated with the engine mounted generators) were powered up at the same time, after 248 days of continuous power, all four GCUs will go into failsafe mode at the same time
Translation: clearly here the FAA is only talking about the
four GCUs related to the engines,
not the other
two GCUs related to the APU.
And notice this simultaneous failure only occurs "if the four main GCUs ... were powered up at the same time".
Translation: if the four main GCUs were
not powered up at the same time, failure in one GCU will not cause all others to fail.