I have a question just to satisfy my curiosity.
Back in the fifties or maybe even earlier there was a
department store in Washington, Dc. That had Otis elevators
which were automatic.
The doors, car and hall, seemed to operate independently of
each other, in other words when the doors closed the car door
would start to close with the hall door lagging behind it, the same thing
would happen when they opened, one door would start to open first with
the other one following either ahead or behind it.
I mentioned this to an older elevator mechanic who retired years ago and
he sort of remembered something about one set of doors being electric and
the other one being operated by compressed air, is that possible?
Can anyone explain in more detail how this worked and why a system like
this would be used.
I will have to admit they seemed to work good and not to mention
if nothing else they were fun to watch.

Yes, the freight hoistway doors used to be pneumatic. The car gate was electric. Possible there were standard hoistway doors using air also. I was a helper when I first saw this.

Otis made an operator which had a small geared machine on top of the car. The machine lifted a weight on the side of the car, like a retiring cam. This weight connected with a lever system that replaced the broken arm style opener on the hoistway doors. When the weight was lifted, the HW doors were closed and when the weight was lowered, the HW doors opened. I want to say it was an A, B, or AB style operator. I haven't seen one in about 20 years, and the last ones I worked on was about 40 years ago. They used them in a lot of Department stores and a lot of Federal buildings. It was an expensive option.

I had them at Fredrick and Nelson (Now Nordstrom) in Seattle OTIS type A, see Unitec poster link below.

http://www.unitecparts.com/wp-content/uploads/2013/03/Unitec-Door-Operator-Poster3.jpg

A type on the right (white one)

I had the door link to the hall door come off and had a report of the car flying by the lobby at full speed with the hall doors open. I ran over to find the car doing just that. The weight on the sill trip that opened the hall door was in the closed position (cam retracted), but because the link had detached from the hall door, controller saw it as safe and door closed.

It was a monster with cams, chains, oil checks and a mechanical brake.