What is this HFACS deal and what’s the difference between HFACS and SHELL?

What is this HFACS deal and what’s the difference between HFACS and SHELL?

Is it a proactive or reactive thing? What does that have to do with identifying tracking errors? Gotta ask, and what’s so important about error tracking anyway. Fix it and fly it!

What does this have to do with identifying tracking error in a safety program?