Page 25 - Volume 15 Number 10

In fact, since observing the battery charging or not charging is a part of the tests to come, I recommend that we not use an EPU for this start. Make it a normal battery start of the first engine and a generator- assisted start of the second engine. That leads to the battery charging at a rather high level.
During the test procedure we want the inverter to be on if we have one. (Both inverters in 350s that have two.) The latest models have gone entirely DC (Direct Current) with no need for an inverter providing AC (Alternating Current). However, we do not want the avionics on yet. Not to say that they will be damaged during the tests to come, but since there will be momentary bus power interruptions it is preferable to not have the avionics subjected to any power disturbances.
Also, do not activate the environ- mental system yet. Leave the Cabin Temp Mode selector in the OFF posi- tion. Otherwise, we may cycle the air conditioning compressor off and on during the process.
The procedure begins by moving the GEN TIES switch – located on the pilot’s left subpanel – down to the OPEN, bottom position. This switch has three positions: OPEN at the bottom, NORMal in the center, and MANual CLOSE at the top. This is a lever-lock style of switch that must be pulled out before it will move. However, it springs from the top back to the center when momentarily selected to MAN CLOSE. In the case of the OPEN position, it must be pulled both to go there and to get out of that position.
When the switch is in OPEN, both the left and right generator bus tie relays should open. Both left and right Gen Tie Open Caution (yellow) annunciators should illuminate, and we check that they have appeared.
I like to teach that we have now created two separate, single-engine airplanes. Yes, it’s corny, but it helps get across the idea that the left and right sides of the electrical system are no longer connected. They aren’t communicating with each other. Also, since the battery connects to the center bus – a bus that can no longer receive power from either generator due to the ties being open – it should no longer be charging. If your particular serial number King Air has a dedicated battery ammeter in the overhead panel then merely verify that the charging current is now zero.
For earlier models that do not have a battery ammeter, the way we must verify that the battery is
indeed no longer charging is to note the loadmeter readings before we move the Gen Ties switch to OPEN and then note the reading afterward. There should be a major drop in gen- erator load, generator output. After- all, except for some lights perhaps, we haven’t activated any aircraft system, so the battery’s charging is the only significant electrical draw that we have.
One time in a zillion we may find that the battery is still charging. Not good! This is an important squawk for maintenance to repair. Either one of the bus tie relays is still closed – which is highly unlikely if the annunciator appeared – or else a diode is allowing current to flow in the direction it shouldn’t.
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OCTOBER 2021
KING AIR MAGAZINE • 23