Page 18 - Volume 12 Number 1

Ask the Expert
Rambling Replies
by Tom Clements
When readers send a question to me or Kim Blonigen, our editor, I try to respond directly without delay. Some questions concern a specific item that affects so few operators that publishing the reply here in my monthly column would merely be wasting ink. However, some questions lend themselves to a wider audience. This month I am publishing some of those questions and my responses in the hope that they will be of interest to most of our King Air owners and operators.
Starting Procedure for Newer versus Older 200s
This question comes from Xandi Newell in Charlotte, North Carolina:
We have a question for Tom Clements regarding the King Air B200’s electrical system. We operate two King Air B200s: serial numbers BB-1246 and BB-1613.
On serial numbers prior to BB-1444, the generator is turned off prior to cross-starting the second engine to prevent blowing a current limiter. This requirement is not necessary for BB-1444 and after. There is much debate among our pilot group as to why the difference exists, with some speculating that the GCU prevents the operating generator from producing excessive current during generator-assisted cross-starts, but we cannot find any documentation that states this directly.
Could Mr. Clements shed some light on this for us?
This was my reply:
Yes, just as you theorized, the GCU limits the output of the operating generator whenever the opposite start switch is activated. This current limiting began with the 300-series, but was added to the 200-series at BB-1444.
With a department such as yours that operates 200s that fall both before and after the change date, I suggest that the earlier procedure – generator-assisted start, not a generator cross-start – be used as SOP for all the 200s you fly. Leaving the generator on increases the chance of experiencing a current limiter failure during the cross- start on the earlier airplanes, whereas doing the Off-On
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procedure does not harm the later aircraft in any way. In fact, I think it marginally reduces starter-generator drive spline and brush wear, as well as reduces the ITT rise slightly on the operating engine. By standardizing on the earlier procedure, it eliminates the “Which one am I in today?” thought process.
One additional comment, as discussed in my book: If the stabilized N1 speed of the first engine, on the battery, exceeds 16 percent – i.e., “Meets your expectations” – then you are wasting time and effort to charge the battery between starts. It’s certainly not incorrect to do so, but rather is unnecessary. So get to High Idle on the first engine, turn its start switch off, activate the other start switch, then turn the first generator switch on (Reset - Pause - On) as the second N1 gets past 12 percent or so. It saves time and can be done for all models of the 200-series. Only if the first stabilized spool-up is less than 16 percent do you need to do battery charging between the starts.
Thanks for the good question and never hesitate to ask if I can help with other questions.
My reply sparked a follow-up question:
Good morning to you, Tom!
Thank you very much for the quick response regarding the GCU on starting the different King Air 200s. It was such a delight hearing directly from you and I really appreciate the time you took delving into the differences.
I do like the notion of keeping things consistent when operating the two different serial numbers. So far, (where’s that wood upon which to knock?) I have been able to keep the two separate by always verbalizing the elements of the starts as I go along, but we all know there will be that one time... Since it’s not hurting anything, I’ll adopt that standardized procedure right away. Thanks!
I have a copy of your book, so I do indeed recall your mention of charging the battery between starts being unnecessary if we see spool-up upwards of 16 percent. What I do wonder, however, is why we wouldn’t need to introduce fuel on the second engine prior to turning on the generator of the first engine. You write: “So get to High Idle on the first engine, turn its start switch off, activate the other start switch, then turn the first generator switch on (Reset - Pause - On) as the second N1 gets past 12 percent or so.” Our checklist for the BB-1246 King Air B200 has the step of bringing condition lever on second engine to Low Idle when we get past the 12 percent, and then turning on first engine generator.
JANUARY 2018