The "Foot Team" has to make sure the feet stay in the holes with their pinch bars. Their job is to help keep the feet in the holes going up, resisting the outward thrust as the gantry rises toward a 90 degree angle, then resisting the reverse thrust when the load is being lowered. The Foot Team and the Team Leader should have their eyes on the load and the gantry at all times.
The load should slowly begin to rise and the Team Leader (get out your pinch bar) should arrest the tendency of the load to pendulum. I have seen an unchecked load swing up to knock out the ledger (in this case a ledger board) and kick both feet forward. Needless to say, it wasn't pretty.
Realize that an impact perpendicular to the long axis of the gantry legs could prove catastrophic. Again depending on the size of the load, the load is usually moving slowly enough (the Haul Team is on a 20:1 system after all) that simply planting the point of the pinch bar into the ground ahead of the load has often slowed the motion down.
The key for the belay team is to allow as much slack as possible while not letting the gantry get ahead of them for the descent back on the other side. As the gantry becomes closer to 80 or 90 degrees, the Team Leader should be notifying the belay team to begin slowing the movement of the gantry. The haul team should be pulling away at the command of the Team Leader, resetting as necessary. If you have the luxury of extra personnel station someone at the progress capture device.
As the load gets to 90 degrees, the team leader should continue to insure the load passes between the legs smoothly (this could also be accomplished with a tag line). As the load passes over the centerline, the haul team must stop hauling and the belayer needs to take up slack and slowly guide the load back down to 45-degrees on the other side, remembering all of our earlier discussion, especially in regard to the load's momentum and the rope's tendency to elongate.
As rope has some give, belaying the load is best acquired through practice or under the supervision of someone who has done this before. There is a certain amount of finesse involved in just allowing the line to become taut as it NEARS centerline (the momentum of the load will facilitate some initial rope stretch) and then, as the rope is stretched to maximum and is bearing the weight, allowing the load to go softly to ground.
Using the rope below 45-degrees in either direction will result in the load on the rope exceeding 130% of the load weight. Once the load is at 45-degrees again and the load is on the ground, have the haul team move up and assist the gantry in going to the ground by walking it back, again, like walking down a ground ladder. The 4x4 used earlier can be utilized here again as well to elevate the apex, making it easier to work.
Substitutions and Comments
I learned how to make an a-frame gantry for the first time in 1981; the text we used at that time was Dawson Nethercutt's International Manual of Basic Rescue Methods. Since then, we have done this a lot of different ways and I've seen it taught a lot of different ways. The point I'm trying to make is that we have outlined the basics and they require you to go play with them a little and challenge yourselves.
The concepts are sound; we are taking a heavy weight, lifting and moving that weight using a mechanical advantage, and distributing that weight to ground by way of columns, or in this case, the legs of the gantry. This year I presented this subject at the South Carolina Fire Academy's Rescue School 2003 and 64 students offered different suggestions and solutions.
My suggestion: take what you already know about lifting and rigging, use a heavy (but not dangerous) weight, consider this article, and practice. You may never use an a-frame gantry in a rescue situation, but the individual skills utilized and the teamwork required in putting it all together are something you can use on every single incident.
Two quick suggestions: A solution to avoid the congestion at the apex with all of those slings; First, use a chain sling instead of a multi-wrap anchor sling as the connection for the load at the apex. After all, if you use an adequately rated sling, what are you going to pick up that's going to break it? Furthermore, the chain is easier to spot with all of that rope around that point. Chain doesn't usually slip, and it generally simplifies the process. Finally, instead of making all of these anchor slings, terminate the haul and belay on the apex using tensionless wraps around the apex.