TWA Convair 880
Had I paid attention at the time, I might have thought that this, N801TW, was TWA’s first Convair 880.   But I would have been wrong.  Although the prototype was indeed registered N801TW in the beginning, things got a bit complicated.   The prototype was reregistered N8499H while under test and modification work with Convair, and again as N871TW when TWA bought it in 1964.  This N801TW was delivered in 1961, during which time the first N801TW was in flight test at Convair.  I at first had these facts all twisted around and I thank Jon Proctor for clearing things up for me!

TWA used the 880 primarily for coast-to-coast routes, but always with a stop in Chicago, Kansas City, or someplace else in the Midwest.   There were other schedules going through places like Columbus, Pittsburgh or Denver.  You can’t quite make out the sign on the boarding stairs, but my recollection of the time of day and a 1964 TWA timetable suggest that this was to be the origination of flight 121, leaving Philadelphia for Chicago, Las Vegas and Los Angeles in the mid afternoon.  An example of the 880 in Delta markings had begun its taxi from an adjacent gate for the afternoon flight to Baltimore and Atlanta.

TWA used the 880s until 1973-74, at which time they were phased out in favor of more efficient 727s.  The cockpit section of the original N801TW (later N871TW) survives at the Delta Airlines Museum in Atlanta.
 

Philadelphia, 1964