Page 28 - Volume 13 Number 9

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 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 the outboard area. Inboard: Less rolling moment arm; Outboard: More rolling moment arm.
Compared to the King Air 90-and 100-series, the 50-inch wider wing center section of the 200- and 300-series means that flap asymmetry will contribute more roll force than before. Therefore, these later models incorporate a Split Flap Protection system. As we have discussed, a drive shaft failure that renders both inboard or both outboard segments inoperative simultaneously leads to no roll tendency. It is only when one segment stops and the other three continue working that asymmetry occurs.
The Split Flap Protection system works in this manner: The Flap Control electrical circuit – the same circuit that includes the switches that the flap handle actuates and the limit switches – includes two additional switches. They are connected to the leading edges of the flaps, one
26 • KING AIR MAGAZINE
SEPTEMBER 2019