Page 26 - Volume 15 Number 5

More than anything else, here is what I want you to retain about the rudder boost system: Pretend it’s not there!
I have come to worry that some King Air pilots think this great system – and especially when combined with the wonderful autofeather system – makes it easy for the pilot to handle an engine out emergency without forceful control input. Wrong! Fly the airplane! Step on a rudder pedal forcefully to maintain heading. Pitch for proper airspeed. Conduct the engine failure memory drill. Yes, you can rest assured that the rudder boost and autofeather systems are reducing your force inputs, but you still need to input whatever is necessary! It’s a rudder boost system, not a rudder replacement system!
More about rudder boost history: Once Beech had designed this
fine system and the parts that made it up were readily available, the decision was made to make it standard equipment across the spectrum of newly-designed King Air models. Hence, all models that were developed and certified after the model 200 have RB as standard equipment: F90-series, C90A and after series, and the 300-series. Only the 300-series require it. Personally, I wish the later-90 series did not have it. Why? Because much too often I have observed pilots undergoing training use too much rudder input, not realizing that rudder boost was helping with a lot of the force. Again, this is shown by flying with the dead engine down, not raised up. In my first book, “The King Air Book” I made the crazy comment that a C90A needs rudder boost like a fish needs a bicycle ... but it’s true. Sure, if it’s there use it, enjoy it, but please keep a close
eye on the changing rudder force/ rudder trim needed to fly properly coordinated.
The system in the 200-series and all of the later C90A and F90-series that have it, is an “all-or-nothing” system in which the pedal force applied is constant when working and zero when idle. The force that rudder boost applies comes from pneumatic servos in the tail of the airplane and the trigger that tells the system to operate measures differential engine power indirectly by looking at the difference (P) between unregulated bleed air (P3) pressure. It is easy to change the point at which RB activates in the various models by varying the value at which the P switch activates. Also, by adjusting the pressure going to the pneumatic servos the rudder force can be easily changed to the value needed for a particular model ... less for a C90A than for a 200.
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24 • KING AIR MAGAZINE
JUNE 2021