1976 Yuba City School Bus Wreck

This probably isn't the right section... if not, the mods seems to instinctively know what to do with my posts

I was reading up on the Yuba City bus disaster that happened in 1976. Something about it isn't making any sense. I'm assuming that air brakes commonly used on buses and trucks have been the same basic design for ages and that's probably where my problem comes in.

The bus in this wreck was a 1950 Crown bus. From what I can tell it may have had a gas engine, since one site hinted that Crown didn't switch to diesel until 1954. But it did have air brakes.

The driver was new to this bus and mistook the low air pressure warning light as the low oil pressure light. The low air pressure was caused by a worn compressor belt.

When the pressure dropped, shouldn't the brakes have applied automatically? The light was on and one survivor mentioned that he saw the driver push the brake pedal to the floor 3 times before the wreck, which would have dropped the pressure even more below the red.

The NTSB report on it isn't all the helpful (NTSB-HAR-77-2).

What going on here? Was the compressor working just enough to keep the needle in the 'warning' range and out of the 'pop' range? If so, shouldn't he have had brakes?

 

That appears to be what's going on.

The bus had a separate system for the emergency brakes. The NTSB report mentions that if the driver had recognized the problem that he could have applied the emergency brakes manually. I was thinking that current method of the brakes applying automatically had been around well before 1950, but as trucker said, it wasn't available then.

I can't find any info on the setup on that bus specifically. But now that you've mentioned it, I do remember reading about a setup like that. I'll keep trying to find a diagram somewhere on it.

And thanks guys. It had me a bit puzzled.