One on the smallest pieces of a goaltenders equipment has had one of the biggest impacts on the modern technique of the position. The landing gear is the small padded flap that comes into contact with the ice when the goaltender drops into the butterfly. It is highlighted below by the top arrow in this picture (this is the inside portion of the pads, ignore the bottom arrow):

This angle shows the knee stacks, which are the inner padded portion of the landing gear:

The immediate purpose of the landing gear is clear: cushion the knees when they impact the ice when dropping to the butterfly. Without these, you are slamming your knees directly onto the ice surface, and that's a painful proposition. But this only occurs in concert with another advance in pad design. Modern goal pads incorporate generous pad rotation which allow the pad face to stay 90 degrees flush when executing the butterfly. Many goaltenders prefer a very loose strapping system to aid in this. See below for a bit of an extreme example. Notice that the straps are nearly on the last notch:

Cushioning the knees for an explosive downward butterfly is not the only revolutionary aspect of this equipment change. In conjunction with the calf wrap, the landing gear creates a smooth pad surface allowing for efficient backside pushes across the ice when in the down position. See below for an execution of the backside push.

Here is the load:

and here is the push:

and the final block:

click here for the ingoal article outlining the backside recovery with video as well.

As is usually the case with my posts, I like to compare and contrast this change with classic goaltending. Note that there is no flap on these pads specifically dedicated to cushioning the knees for the down position:

In spite of this, it would be foolish to say that goaltenders of yesteryear did not execute the butterfly because they did not have this equipment innovation. That is the case mostly due to definition, however. Back in the day, it wouldn't have been called a butterfly, but more or less just "dropping down", and that could look vastly different in execution:

Notice Glenn Hall in that last picture. This is close to what we see in the modern butterfly, but the pad rotation is not there, so the tendency of the pad is to land with the knee rolls tucked in and the pads on an angle, versus flush 90 degrees to the ice in todays pad design (this helps alleviate the lack of knee cushioning old pad designs had because landing on the knee rolls had better support for the knees). This is also in conjunctgion with old school tenders securing their pads much tighter than their modern counterparts. Classic goaltending also did not have the emphasis of the powerful "drive" downards to the ice that todays butterfly has. Many goaltending coaches use the phrase "pretend you are going to drive your knees through the ice," in order to instill a quick closure of the five hole. Its hard to imagine such a mentality without the aid of a padded landing gear.