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Ed Anderson wrote:
Ernest, I could be wrong, but seems I recall somewhere that FAA requires a
fuel shut off valve. Someone else may know whether that is correct or not.
For the reason you stated - Safety.
Ed A
I don't doubt that it is so, Ed, but putting the edicts from Federal agencies aside, I'd like to raise the question of whether it is safer. I mentioned two instance where a valve for a single tank system would be useful, an inflight fire and emergency landing prep. In both instances, the pilot is required to remember to throttle back, turn off the boost pump and then turn off the manual valve under the worst of circumstances. Unless it is very well practiced, most pilots will have to look around for the switches and knobs, taking their attention away from other duties. If you're going in under partial power, you may not be wanting to give up that power until very short final, moving the list of task to the most dangerous times. A throttle with a cutoff switch wired into it that would cut power to the pump after being pushed past a detent would accomplish three disjointed operations in one intuitive step, and leave the pilots thottle hand on the throttle.
Assuming that connections will be the weakest spot in any system, and that there actually is a pump that blocks flow when there's no power applied (I haven't tried to determine if there is), I would argue that the pump IS the cutoff valve, and that adding a pilot operated manual valve actually reduces safety by needlessly increasing complexity and pilot workload.
Marc, is quite right that the fuel system is a pain to work on when the fuel can't be contained in the tank. But does this argue for a pilot accessible fuel valve, or one directly at the tank exit? I think it might be different issue from what I was first asking about, but interesting nonetheless.
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