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The other king airs have a monkey motion abortion of electric motor, bell cranks, and bicycle chains.....somewhat more prone to failure.
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That's a somewhat polite description.
There's also drive shafts and jack screws. The jack screws have to periodically be removed from the mains and inspected for play.
The emergency extension system is a ratcheting handle that turns a bicycle sprocket that drives a chain connected to the transmission that the motor is mounted on (you have to first pull another handle that disables the power to the motor and engages the chain). You pump the handle until the lights indicate that the gear is down, then stop pumping.
If you keep pumping until the handle locks up (on the 200 - not sure about the others), some poor mechanic is going to have to pull the copilot's seat, the partition behind the copilot's seat, and the side facing couch that is usually just aft of that partition, then pull up the floor in that area. They then will spend a considerable amount of time cussing as they pull two small bolts and loosen a third one on the bearing housing that the sprocket is mounted to, just to get the tension off the chain so that the emergency system can be disengaged.
I've told pilots that they won't get any grief from me if they have a gear motor failure and jam up the system by pumping until the handle binds up. They've got too much to worry about in a situation like that, to bother thinking about what some mechanic might get stuck doing. Mechanics, on the other hand, should expect much laughter at their expense, especially if they had been warned before they did it.
One of the apprentices suggested that a new IA talk to me before using the emergency extension system during a gear test, and he led the guy over to the small maintenance hangar to find me. I explained what not to do, and what they would have to do to fix it if they screwed it up.
IA: "Well, I've got years of experience working on King Airs, and I've never heard of such a thing, and never had any problems using the emergency extension system."
me: "Ever work on a 200, before?"
IA: "No."
me: "It'll do it, every time you pump the handle until it won't pump any more."
He harrumphed, and they went back to the big maintenance hangar.
About 20 minutes later, the apprentice came back over and asked "Exactly which floor panels did you say would have to be pulled?".
ETA: One possible way for the gear to fail, is a weak, worn out gear motor can get hot while retracting the gear, causing it to pop the circuit breaker. The circuit breaker for the gear motor is underneath the center floor, aft of the power lever pedestal. The pilots cannot reset that breaker, unless they happen to have brought the necessary tools with them and one pulls the floor up while the other flies.
As a bonus, the motor is under a greater load while retracting the gear in flight (the mains are pulled forward and up, against the airflow), than while retracting the gear on jacks in the hangar, so it may or may not pop the breaker when the mechanics are trying to figure out why the system failed in flight.