Originally Posted by
John Eacott
Have advances in engine control/management introduce unnecessary complications, eg this switch to turn the engine 'Off'?
My antique experiences of jet engine management were all back in the analogue computer days, but the vast majority relied on pulling the SSL (Speed Select lever) back past a mechanical lock to shut off or rolling the throttle back past a pilot operated mechanical lock to shut off. In all cases the lock occurred at ground idle.
So maybe something similar is not inconceivable in this digital age, incorporated into the Thrust Levers quadrant and removing the intriguing but IMO unnecessary switchology and computer processing of the Fuel Shut Off switch?
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).