Originally Posted by
RatherBeFlying
Not advocating so much as putting up for discussion. I suspect the certification authorities later decided against continuing the practice as it may raise more problems than it solves.
You got that last part right. For starters, any single 'switch' would violate 25.903(b):
(b)Engine isolation. The powerplants must be arranged and isolated from each other to allow operation, in at least one configuration, so that the failure or malfunction of any engine, or of any system that can affect the engine, will not
(1) Prevent the continued safe operation of the remaining engines; or
(2) Require immediate action by any
crewmember for continued safe operation.
So, at best, you'd need an independent system for each engine. Further, you'd need to come up with a G load that is both low enough to be survivable, yet at the same time high enough that the aircraft can't possibly still be airworthy - for example a very hard bounce, the pilot decides to go around, but your crash switch shuts off the engines and they crash due to the crash switch...
Where do you put the G switch - different parts of the aircraft can experience vastly different G loads in a hard landing. Oh, and for what should be obvious reasons, the regulators have taken a very, very dim view of any system that can unilaterally shut down an engine in-flight. Boeing has "Thrust Control Malfunction Accommodation" - TCMA - that will shutdown an engine that remains at high power with the throttles at/near idle - but it's only active on the ground. What sort of air/ground indication would you trust to still function and function properly when you just hit the runway so hard that the landing gear came off?
I worked engines for nearly 40 years - wouldn't touch a system like that with a ten foot pole. It would make MCAS look positively brilliant.