This is a short anecdote that illustrates what Kevin is talking about: I was fireman on SVRy 19 one day when I noticed we were slowing down for a reason unknown to me. I started making necessary adjustments to the fire. I looked over and the engineer was dropping the johnson bar a few notches muttering something like "what's going on here", but we are still slowing down. We both realized about the same moment that the throttle had closed on it's own. The spring on the pawl had broke. Much safer to have it close than be overbalanced to open!