Adam, there are several possible failure modes that will result in a collapse. Certainly a problem in the hydraulic circuit can be one such cause, often by the inadvertent retraction of the gear when the pilot meant to reach for the flap lever. The design intent of the gear is that drag strut should be adjusted to go "over center" upon gear extension. In addition to the static force of the hydraulic cylinder there is a spring designed to hold the strut in this position. Because there should be virtually no "retraction" force acting on the drag strut at this point, even the relatively small spring should keep the gear extended. Remember the hydraulic power pack does not maintain pressure on the actuating cylinder after the level pops back to the neutral position. If there is a leak anywhere in the system the hydraulic cylinders are not actively holding the gear down with any force - only force is coming from the spring.
Now, looking beyond the hydraulic system a frequent cause of gear collapse is the bracket that attaches the drag strut to the rear spar. This, of course, was the subject of a recent thread which we all participated in. Another failure can occur if the scissor mechanism fails, usually due to a problem with one of the bolts.
I did have an email exchange with the owner of the plane in the Falcon Field accident. The gear collapsed after a normal landing. Sadly this was a demonstration flight with a prospective buyer of the plane. He did indicate there was minimal damage to the airframe, but an engine and prop teardown will be necessary. The owner does not yet know where the failure was and given his obvious grief over the situation I did not press him for more information. As time goes by we will learn more.
