United Viscount 525
This is one of about 47 Viscounts that United inherited in the Capital Airlines merger of Jume, 1961.   Although the Electras were much more widely used in the U.S., the Viscounts had good passenger appeal with their large windows and jet power.  United's were operated as all first class with around 42 seats.  As good as all of this may have been, many will remember the Viscount by its ultra-distinctive whine -- some would say "screech" -- coming from those Rolls Royce Dart 525 engines.   Many of us would like to hear one taxi by right now -- and others wouldn't!   Regardless, it won't happen, but you can go here for a sound clip in the Flight Simulator section that sounds fantastic.

Philadelphia, 1963