Separately, I remember on the 727, with the engines shut down, we would sometimes check the interlock. With the thrust levers(TL's) fully aft, the reverse levers(RL's) could be selected. When the TL's were moved only slightly forward from the closed position, the RL's were mechanically blocked from being selected. Likewise, if the RL's had been selected, the TL's could not be moved forward from the fully aft position. I suppose that is different than an engine staying in reverse by itself after deselection as happened in this incident.
I believe that this is all mechanically located in the Thrust Lever unit.
I thought that was standard on all types.
I could be wrong again though.
