I also feel that the Automatic air is safer over the range of situations. However, on long grades an inexperienced engineer can be "out of air" with the automatic system. If the engineer cycles his brakes too often or too quickly, he will deplete the air in the resevoir, and have released the air from the cylinder. the result is no brakes and no air. The obvious solution to this problem is the retainers,which hold the air in the cylinder longer durning a "release", allowing the resevoirs to completely recharge.
Also, if the brake pipe is reduced to 65psi (assuming a normal 90psi brake pipe), further reductions of the brake pipe do not yeild any more braking power. This is true on the old K valves and such. The newer AB, ABD, etc brake valves also employ an emergency resevoir that would further increase the air pressure, but the train has to go into emergency to do it. This is a problem if the brakes are not able to hold the train back, or if too much of the trains brakes are cut out. (As I'm sure you know, no more than 80% of any train's brakes may be inoperative at any time, 0% is favorable, obviously)
The benifit of the straight air system is that it does not leak down provided that the straight air train line is intact. YOu never run out of air on a straight air system--> unless you separate or loose a hose. Then the operation of the Automatic system becomes imperative.
The result is that the straight air system reduces the chance of a runnaway, but only if combined with the Automatic system as an immediate back up. Likewise, running out of air on an Automatic system is fatal, unless backed up by a functioning straight air system.
The bottom line is to have good operative systems, know how to uses them, and don't take unnecessary chances.
My penny and a half's worth!
Ryan Scott
