Originally Posted by stilton
Not to belabour the point, but why does the 767 have the PES and not the 75
Any ideas?
Good question.
Here's one theory.
When you and I fly these jets, they are basically the same, or at least very similar. To the maintenance and engineers, they are two different airplanes.
The 757’s are assembled in Renton, WA and the 767’s are put together in Everett. The design teams are two different groups, and perhaps they did not confer on every aspect of the jets.
Apparently the 767 design team thought that pitch control was a critical item, and so designed the PES as a redundant system.
The 757 does not have a PES for pitch control, but does have the PTU to operate the “flaps, slats, gear, and steer” in the event of a Left Engine failure or in the event of a failure of the Left Engine-driven hydraulic pump.
Maybe one team thought the pitch control needed redundancy while the other team thought that the “big four” needed redundancy.
There may be other theories out there as well.