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The flap motor, gearbox, drive cables and Dynamic Brake Relay.
Inside of the flap gearbox or transmission showing worm and worm gears.
shafts experiences a stripped gear such that the motor cannot drive it, then we would lose both left and right inboard or both left and right outboard flap segments ... it would never present us with an asymmetrical situation.
In 1975, a colleague of mine was delivering a factory new E90 to Beechcraft West, a Beech distributorship in Southern California, located at Van Nuys (KVNY).
In those “good old days” no flight restrictions existed over the Grand Canyon so on their descent into Las Vegas for a refueling stop, they were enjoying the canyon views while descending near redline speeds over the Colorado River. As the passengers “oohed and aahed” their way in the descent while the pilot S-turned over the canyon, my friend suddenly felt the airplane balloon upward. “Oops, I think I just touched something!” said the passenger sitting in the co-pilot’s seat. It didn’t take long to realize that the passenger had accidently moved the flap handle from Up to Approach as he was leaning over to look out of the left-side cockpit windows. (This incident led to Beech adding the little “wall” on the right side of the flap handle to decrease the chance that it could be moved accidentally.) The pilot retracted the flaps and continued to Las Vegas. He used 100% flaps for landing and all was well. But as he taxied to the FBO, Ground Control said, “Hey, King Air, your inboard
MAY 2023
flaps are up, but your outboard flaps are still down. You aware of that?”
Until then, he was not aware of any problem. When the flaps were accidently sent to the Approach position at a speed well over the limit, apparently the teeth on one of the transmission’s worm gears had been overloaded so that they were weakened enough such that they failed completely in another couple of cycles.
For split flaps to occur – by this we mean one segment being out of sync with the three others – we must have a jackscrew failure: Either the jackscrew itself is faulty or the jackscrew is not being driven by its drive cable: the cable broke internally or it became disconnected from the jackscrew or the transmission.
Twice in my flying hours I have personally experienced split flaps. Once was in an A90 – that I talk about in The King Air Book – and the other time was in a Duke ... that has a single flap segment per side, unlike the King Air. In both cases I was very pleasantly surprised to find that the outcome was basically a nonevent.
Further analysis suggests that this is not too surprising since the lift/lack-of-lift this malfunction causes has an asymmetrical force acting on the wing’s inboard area whereas the aileron and their trim tabs apply force on
KING AIR MAGAZINE • 19