Hi,
Events surrounding auxiliary power unit shutdown.
1000:24 Airplane touched down.
1004:10 APU started.
1006:15 Airplane completed turn into parking location.
1006:48 Parking brake set.
1006:52 Engine 1 shut down.
1006:54 Engine 2 shut down.
1021:01 APU battery bus voltage decreased from 32 to 31 volts.
1021:04 APU battery current increased to between 44 and 45 amperes for 4 seconds, indicating
current flowing into the battery.
1021:07 APU battery bus voltage decreased to 30 volts.
1021:09 APU battery bus voltage decreased to 29 volts.
1021:10 APU battery bus voltage increased to 31 volts.
1021:15 EICAS message discrete indicated that the APU battery failed.
1021:27 APU battery bus voltage decreased 1 volt per second during the next 3 seconds until
reaching 28 volts at 1021:30.
1021:37 APU battery bus voltage decreased to zero volts and returned to 28 volts three times, and
APU battery current began to move between zero and -4 to -5 amperes, indicating current
flowing out of the battery.
1021:37 APU controller went offline, and APU shut down.
1021:37 Aft EAFR stopped recording. Forward EAFR continued recording for about 9 minutes
58 seconds.
1021:40 EICAS message discretes indicated that the left and right 1 and 2AC buses became
unpowered.
1021:41 EICAS message discrete showed that the APU battery failure was no longer indicated.
1022:00 EICAS message discrete indicated that the main battery was discharging.
1022:10 APU controller was back online.
1022:53 EICAS message discrete indicated that the main battery power switch was off.
1023:16 Airplane systems providing data to the EAFR had shut down.
1031:35 Forward EAFR stopped recording.
Note: EICAS, engine indicating and crew alerting system. The APU controller is the source of 32 recorded parameters,
includingAPU shaft speed and APU battery bus voltage.
1021:37 APU battery bus voltage decreased to zero volts and returned to 28 volts three times, and APU battery current began to move between zero and -4 to -5 amperes, indicating current flowing out of the battery.
After the battery failure (1021:15 EICAS message discrete indicated that the APU battery failed. ) the (failed) battery was still in the circuit!
1021:01 APU battery bus voltage decreased from 32 to 31 volts.
1021:04 APU battery current increased to between 44 and 45 amperes for 4 seconds, indicating current flowing into the battery.
This is another
point:
If (as it seems) batt. was out of circuit and itīs voltage suddenly drops the algorithm should verify WHY, before trying to charge at this rate.
So, in a first look (still lacks info) we may think the charging system "aggravated" the problem (
one cell probably "failing=shorting")