Originally Posted by
aeromech3
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Out of interest, even the very classic B747 with JT9's had an interlock, by way of an electrical actuator in the pylon area, which prevented forward throttle movement whilst the reversers were not stowed.
Sorry, nerd mode coming out...
The JT9Ds did not have an electrical actuator in the pylon, it was a mechanical block. The mechanical block was connected to the reversers by feedback cables - it prevented 'advancing' the thrust levers to 'higher' reverse thrust until the reverser was ~85% deployed, then prevented moving the thrust levers into the forward quadrant until the reverser was ~85% stowed (e.g. 15% deployed) (being a mechanical device, there was some variability in the exact T/R positions). The same mechanical block would move the thrust lever to idle if the reverser moved out of its commanded position for some reason. There was a similar system on all pre-FADEC Boeing installations.
With the advent of FADEC, that mechanical system would rather obviously no longer work, so an electrical actuator or solenoid was in the flight deck thrust lever quadrant that served the same function of preventing high reverse thrust until the reverser was deployed, and forward thrust selection until the reverser was stowed - feedback was from electrical sensors on the T/R actuators - which also allowed the FADEC to limit thrust if the T/R was not in the commanded position.