The post suggests that they weren't robust enough. That's why I said systems and procedures--backup systems don't work if the guys monitoring them aren't well-t

The post suggests that they weren't robust enough. That's why I said systems and procedures--backup systems don't work if the guys monitoring them aren't well-trained or paying attention because everyone assumes the GPS is infallible. Policies based on GPS MAD would place a lot more attention on the non-GPS systems.