One little problem happened a few days ago to confuse my already confused knowledge:
After a scheduled airplane change, we arrived at the new one and found it completely dark with an engineer struggling in the cockpit.
Apparently, as he told me, somebody
had forgotten it with the battery on... so the battery was depleted and the APU couldn't be started.
Long delays waiting for a GPU, of course, at LIRF
Then the AC GPU came and he was able to start the APU.
This confuses me a bit: doesn't the APU require Battery power to be started?
We were told in the classroom the Apu starting excludes the battery charger because it is limited to 40 amps, and only the battery can provide the sudden huge amps amount to crank the APU, as in theory it can provide a million amps in one millisecond...
This seems to be confirmed by the BAT ammeter going full negative every time we start the APU normally, with ground power already on line.
So how on earth was it possible to start the APU the other night using an
AC ground cart?
