Originally Posted by barit1
The FAA's recent NPRM action can be seen
here.
Of interest is the FAA's use of the term "unsafe condition" without a quantative threshhold. The CF6-80 has, by any statistical measure, an outstanding reliability record, and the AD proposed will doubtless improve that record. GE would probably love to have their spare parts sales blossom as a result of hardware retirement, but that will create an economic burden on the industry that may raise ticket prices and drive more pax onto the highway. How much safer is that?
Oh I would say that there is a quantitative threshold..
At any given time, you are fliyng around with unknowns, about 10 times the number of known problems that you have. So while the reliability record might have been good up to the latest problem identification, you just can't go around ignoring the known stuff, figuring that it's not your turn today.
So you take the known stuff and with some data, (cracks per 1000 engines etc.) you extrapolate out how many more big bangs are likely to occur in the future if you do nothing. If you get an answer anywhere close to one that would indicate that you are using up all your average good reliability record in just a few months of exposure. Clearly not something that either the feds or the operators are prepared to absorb.
The problem with this latest problem is that it is so lethal that you have to err on the side of conservatism to avoid another one like the last one.