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The Phenom 300 require all three gear to be pinned before towing. I assume there are other aircraft with the same restrictions.

The nose gear is understandable, due to the link being pinned out of the way to allow a larger range of movement of the nose gear.

But why the main gear? Does it have something to do with the trailing link style of the mains?

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The most direct answer is that gear pins are installed to prevent accidental retracting during towing. I'm not typed on the Phenom, but the landing gear actuators are most likely hydraulic. Even if they are electric, the airplane is expected not to have any form of power established during towing, making accidental retraction more possible, even if the gear is held in the down position by locks, not its actuators.

The requirement to install the gear pins is not related to the trailing link design. No matter what the design was, that requirement would be there for each gear.

This requirement is ubiquitous on larger aircraft. During airline operations, I have had an aircraft towed over to me many times. I have never seen a plane in tow, at least at my company, that did not have the gear pins installed during towing.

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    $\begingroup$ Great comment, I am a retired A&P and read this question yesterday but had forgotten about this. When I worked for Continental we only pinned the nose gear. But, I noticed aircraft that where having A/B/C checks had the mains pinned too. I also noticed most govt planes i.e FAA pinned all the gear when parked. $\endgroup$ – jwzumwalt Jan 6 '18 at 12:55
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    $\begingroup$ Pinning the gear, for airline aircraft, is much ado about nothing. The main gear can't retract, even with hydraulic pressure and commanded actuation, due to the over-center locks (the nose gear probably could). Consider, have you EVER heard of a towed aircraft have a gear retract? And even better, during towing typically only one hydraulic system is powered, for brakes.But during pushback, engines are being started, both systems are ready for pressure, and are the gear pinned? Nope. Pinned while parked & zero hydraulic pressure is even less necessary than while towing. Tradition, tradition... $\endgroup$ – Ralph J Jan 7 '18 at 1:38
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They’re safety pins, installed not to prevent the gear from retracting while towing - the gear is designed to support the jet during much faster operations on the ground - but to prevent an accidental retraction when maintenance personnel are working on or under it. Gear collapses have killed Mechanics in the past.

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