Canadian Transportation Board filler metal composition criticism

Prior (fall 2013) accident investigation in Canada where the Canadian Transportation Safety Board concluded the under-matching 4043 filler metal caused a fatigue crack. Tom helped the client respond. Reused in §5 as an example of how failure analysts mistake difference for cause.

So this company has been in business for about thirty or forty years. They used to be an authorized repair station for one of the engine manufacturers, and then the engine manufacturer said, we don't want to start repairing our own product, we want to sell new ones. They sold this and the family took it over. Chuck's not part of the family but he's the chief engineer. I scratched out his last name — you don't need to know it. I had worked with him before. One of the problems they had: the housing is an aluminum casting alloy and they were using 4043 filler metal — they'd grind out a crack and fill it up with 4043. As you'll see, 4043 is softer. I had just worked with them on an accident that occurred in Canada, and the Canadian Transportation Safety Board, similar to our NTSB, had investigated and said, your filler metal is softer than your base metal and therefore you have under-matching weld metal, and that's the cause of this fatigue crack.