Page 15 - April 25

After completing your before-start checklist, go ahead
and start your first engine. It does not matter which side
unless you are in a 90, A90 or B90 with a supercharger
on the left side. In those models, the right engine first
is the way to go.
Once the first engine is started, most pilots bring the
generator online to recharge the battery after the start
(prior to BB-1444). Here is where the problem arises.
When you turn on the second starter, it will ask for
approximately 800a to get the engine turning from a dead
stop. The electrical demand will reduce dramatically
after the engine begins to turn. The problem is that the
operating generator is going to produce quite a bit of
that power and send it through the current limiter on
its way to the isolation bus (see Figure 2). Remember
that the current limiter was rated for 325a. Forgetting to
turn the first generator off prior to initiating the second
engine start will set you up for a failed current limiter.
Figure 2
Passing 800a through a 325a current limiter is possible
but not ideal. The current limiter might be able to
withstand that a time or two but eventually passing that
much current through it will cause it to fail.
Now that we have used some power out of our battery,
we have a choice to make. If you are happy with the
max motoring N1 speed you had on the first engine start
(18% or so), then you can skip the battery recharge step
and go straight into the second engine start. Hit the
starter for the second engine and once N1 reaches 12%
or greater, bring the first engine’s generator online. The
generator will now assist in the starting of the second
engine. I would expect to see 20% or greater N1 for max
motoring with the generator assisting. The second engine
start will be significantly cooler than the first engine.
Remember the faster N1 is before you introduce fuel
to the engine, the cooler the start will be. Alternating
APRIL 2025 which engine starts first is a good way to even out wear
and tear between the two engines.
With both engines running but only one generator
online, we are going to do our second current limiter
check. Press the button on your load meter again and
check the volts on both. With one generator on and
intact current limiters, you should see 28v on both
volt meters. If you see 28v on one and 24v on the other,
you have blown a current limiter during the start, most
likely on the side that you started first. Time to shut it
back down and get the failed current limiter replaced.
Taking off in this condition is prohibited as you no
longer have a dual-fed electrical system and the loss of
one generator will cause other systems to fail with no
means of restoring them in flight.
The third and last check of our current limiters is
performed after shutdown but before we turn our battery
off. With both generators offline, press the button on
the load meters one last time. You should see 24v on
both voltmeters. If one reads zero the current limiter on
that side needs to be replaced before your next flight.
If they both read 24v they are good and you can turn
off the battery.
What about 60a current limiters?
The last set of current limiters we are going to talk
about don’t get much attention from pilots but they
are a good thing to check once in a while. The current
limiters I’m referring to are the 60a limiters between
the dual-fed buses and the left and right generator
buses (see Figure 3). The dual-fed buses are protected
by 50a circuit breakers as well as 60a current limiters.
The circuit breakers are located on the right-side CB
panel in King Air 200 and B200s and the fuel CB panel
under the fuel gauges. Circuit breakers are easy enough
to see when the have popped but the current limiters
are a little harder to tell when they have had a problem.
Figure 3
KING AIR MAGAZINE •
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