Originally Posted by
blue up
With regards to the post above, the Britannia incident pushed the dog box up just far enough to snag the thrust lever and reverser cables, but not symmetrically. Looks the same here.
I was, uh, rather close to that particular incident.
Not quite - there are not 'reverse cables' as such on the 757 - on the 757-200/RB211-535, the throttle cable actuates the reverser Directional Control Valve when it's moved sufficiently aft of forward idle. When the nose gear came back through the EE bay, it snagged the throttle cables in such a way that the engines went to high forward thrust - in that condition it is not possible to deploy the reversers. The combination of high thrust and inability to deploy the reversers made for a rather long overrun.
While the design of using the throttle cables to actuate the reverse DCV was common place back then, it has some highly undesirable failure modes. The 757-300/Rolls didn't use that design (I was directly involved in the design change, including having to debate the Chief Engineer who didn't want to make the change).
In the aftermath, Boeing designed a 'guillotine' system - if the nose wheel came back as it did in Britannia, the guillotine was intended to cut the throttle cables in such a way that the engines would go to idle. I think the guillotine was AD'ed but I wouldn't swear to it.