Page 19 - Volume 10 Number 11

wait for a rainy day and find a puddle as you taxi to or from a flight on a paved ramp/taxiway. Stop with your left prop over the puddle. See how much water is displaced while sitting there at Low Idle. Now feather the prop and see what is now happening to the water. Of course, how much surface wind exists and its direction will affect these results so realize that what you are observing won’t always be the same when dirt replaces the water and the existing wind changes. Nevertheless, you will probably conclude that the feathered prop blades do not offer much, if any, benefit in this situation.
After the right engine has completed its battery-only start and is stable at Low Idle, now is the time to turn on the generators. Although doing them one-at-a-time is fine, there is nothing wrong with activating both switches simultaneously. That’s the technique I use. Keep in mind your Low Idle ITT limit since ITT will rise due to the generator load. For it to reach the Low Idle limit is extremely rare, likely only with three-blade props and their minimum Low Idles. When King Airs had NiCad batteries – and a few still do! – the initial generator load went higher than it does with the current Lead-Acid batteries, so the odds of exceeding the ITT limit were slightly increased.
Even though only one reader in a hundred may observe ITT rising to and trying to exceed the Low Idle limit, we must be prepared for that uncommon occurrence.
What to do? Turn off the generators, of course! Next, take the condition levers and add about five percent N1 to both engines and try the generators on again. The ITT still tries to pass the limit? (And this is extremely unlikely!) Turn the generators off again while you add another five percent or so, and try again.
Some of my readers may be wondering why running the compressor faster – which requires more fuel flow – would lower ITT. Realize that as compressor speed increases, the engine receives more air and three- fourths of that air is used for cooling not combustion. It turns out that up to High Idle, 70 percent N1, the cooling effect of the air is greater than the heating effect of the fuel. Cool!
(As a side note: One of my King Air pet peeves is that the Low Idle ITT limit is not marked or placarded in the cockpit in any manner whatsoever! Unless you’ve studied the POH with an eagle eye or received thorough training, it’s a mystery. Well, let me just give them to you: PT6A-20, -20A, -135, -135A: 685° C; -21, -28, -41: 660° C; -42, -52, -60A: 750° C. Notice that all of these are well below the top of the gauge’s redline.)
Before Takeoff Checks: This is not the time for doing all of the first-flight-of-the-day ground checks! That is nearly a guarantee that you will be leaving rock dings on propeller blades, gear doors, flaps, and maybe elsewhere.
NOVEMBER 2016
KING AIR MAGAZINE • 17