LOU wrote on Jul 3^rd, 2011 at 2:18pm:

Mark, when your drugs are finished, the article talks about just that - when to use Mach. If I remember, each plane has a different proper altitude. I think in the 707/727 we used FL 280 to 300 to make the change. Lou

OK. You convinced me to read up on it now. I thought it would be the same for all planes so I got that one wrong! I'm learning lots of new things from you Lou. "And loving it!" - think of Maxwell Smart (Agent 86), from Get Smart, when you read that! ;D

Mark