Originally Posted by
Someone Somewhere
I have seen references to a similar shutoff mechanism on fighter aircraft and I think BBD bizjets. One of the issues is that it's virtually identical to what Airbus uses for reverse thrust - lift the latch, and pull thrust levers rear of idle, and this has apparently caused some inadvertent shutdowns when moving back and forth. Modern engines auto-select ground, flight, or approach idle as necessary.
The switches apparently are not (solely) computerised. They use relay logic to shut the low-pressure fuel valve, and may or may not actually instruct the FADEC to shut down.
Note previous comments by TDR and others that the move to FADECs resulted in a significant (order of magnitude or better?) increase in engine controls reliability - not necessarily engine reliability as a whole, but still a very very significant improvement.
I'd be interested in a listing of all the ways you can shut a typical turbine engine down, and what the delay is on them - apparently the spar valve is quite slow (a minute or two at idle).
The Challenger 600-series and CRJs have a latch mechanism as described, but they don’t have FADECs. The Challenger 300-series and Global Expresses have FADECs and virtually identical fuel switches.
Notably, while no final report has been issued, the Challenger accident in Naples has been suspected to be caused by a pilot reaching around underneath the latches at the same time the PF retarded the thrust to IDLE going past the latch detent into shutoff.
All engine controls shut off fuel at fuel controller, no design uses the spar valves as shutoffs exclusively. The spar valves just isolate the fuel lines in case of fire and back up the HPSOV. I’ve shut off a couple of TF-39s using the valves when the fuel controller valve failed, it’s a wait.