Page 21 - Volume 11 Number 12

is the force applied to the top of the rudder pedals (and from there to the pistons in the master cylinders). If you want and expect the parking brake to work properly – to hold the airplane still even while doing a high- power runup – you need to really push HARD on the brake pedals! Saying, “Oh, the parking brake won’t hold during the Overspeed Governor check; I need to use the brakes myself then,” is almost always wrong and shows a lack of system understanding. If you can hold the airplane with brake pressure, then so can the parking brake, by trapping that same pressure. A leaking check valve is the only valid reason for the parking brake not being able to hold just as tightly as yourself ... and leaking brake check valves are rather rare to find.
So, don’t be afraid or reluctant to really stand on the top of those rudder pedals while setting the brake! Doing it two or three times; pumping the brakes is fine, too, and usually helps by forcing even more fluid to the caliper.
Does the order of parking brake control usage matter? Should I press the pedals and then pull the knob, or pull the knob and then press the pedals? It doesn’t matter one whit! Realize that you are creating a one-way valve, not creating a two- way stop. If the brakes are already being applied by you, just pull the knob to trap the pressure. If the knob is already pulled, just pump the brakes until they get good and stiff as fluid is sent downstream of the check valve.
Not all King Airs have a Rudder Boost system, but many do. When checking the proper operation of this system during the runup, it is very important to have the parking brake set strongly enough that it alone will hold the airplane. If you are not using the parking brake, then you have to apply so much rudder pedal force that you tend to mask the motion and feel of the Rudder Boost system.
I think that most King Air sim- ulators do a poor job of replicating
DECEMBER 2017
the operation of the Rudder Boost system during its test in the real airplane. Almost always, the sims activate too soon, before sufficient difference in engine power is created by advancing only one power lever. Keep in mind that Rudder Boost is triggered by sensing differential power, not total power. The 350 uses torque to measure differential; the other models use raw P3 bleed air pressure instead. (Torque is the better way to go!)
Especially in those P3-measuring airplanes with four-blade props – and, hence, higher low idle speeds – often it takes nearly full power on the “good” side before enough differential P3 pressure is created to activate the Rudder boost “kick.”
Just recently I observed a case in which the parking brake was not set strongly enough during the Rudder Boost test. This allowed the airplane to creep forward as the
KING AIR MAGAZINE • 19