FedEx semi didn't brake before California crash
Source: AP-Excite
By FENIT NIRAPPIL and JOAN LOWY
ORLAND, Calif. (AP) - Federal safety investigators say the driver of a Fedex tractor-trailer that struck a bus carrying high school students didn't appear to brake before a fiery collision that left 10 dead.
National Transportation Safety Board member Mark Rosekind said Saturday that the truck left no tire marks as it careened across a median and slammed into the bus taking the students to a college tour in Northern California.
Investigators also interviewed a witness who said the truck was already on fire before it crossed the median.
The truck and bus exploded into towering flames after Thursday's crash, making it difficult for investigators to determine whether a fire started in the truck. But Rosekind says investigators plan to look at a blood test and other physical evidence to make that determination.
FULL story at link.
Read more: http://apnews.excite.com/article/20140413/DAD4ULSO1.html
The demolished remains of a FedEx truck is towed into a CalTrans maintenance station in Willows, Calif., Friday, April 11, 2014. At least ten people were killed and dozens injured in the fiery crash on Thursday, April 10, between a FedEx truck and a bus carrying high school students on a visit to a Northern California college. (AP Photo/Jeff Chiu)
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The brakes on a FedEx truck, as with most of the trucks in use in the US today, are "S-cam" brakes. This is a picture of the inside of one:
This sits inside a cast-iron drum, to which the wheel is bolted. The black thing that looks like a fat letter S is connected to a brake chamber through a "slack adjuster." There are two kinds of brake chambers on a truck.
The first kind is on the steer axle. In it is an inflatable rubber bag. When the driver steps on the brake pedal, this bag inflates. It pushes on a rod, which is hooked to the slack adjuster, which rotates the S-cam, pressing the brake shoes against the drum and slowing the truck down. All trucks have two of these.
On all the other axles on your truck the chamber's different: there are two bags and a huge spring. The spring shoves the shoes up against the drum and stops your ass in a right hurry. (This spring is made from steel rod 1/2" in diameter. There's nothing subtle about it.) One of the bags is your "emergency brake." Its purpose is to compress the spring, lifting the shoes away from the drum so the truck will move. The other bag is there to compress the emergency brake bag when you step on the brake pedal, which allows the spring to press the shoes against the drum and, as you expected, slowing the truck down. On a five-axle truck there are eight of them; FedEx pulls doubles so there are ten of these on one of their rigs.
If the fire burned through the air lines, all the bags would deflate and the spring brakes would take charge.
Now here's your problem: DOT tubing is nylon - probably for this very reason; if your truck catches fire going down the freeway they WANT the brakes to come on all by themselves. The fire consumed the lines, but you'll never know when...but I don't think it was before the crash.
Very sobering. 
when I was reading the paper this morning about some of the people who died (and there may be more - lots still in hospital), I totally lost it and couldn't stop crying. This one really got to me more than some other tragedies. I don't know why.
Damn, tears again. My granddaughter went on an 8th grade trip back east - the schedule itself was insane). Maybe it was something to do with that, although she has been back for a week, safe and sound. The story about the twins being on different busses really got to me. 
