Avianco
McDonnell Douglas MD-87
The McDonnell Douglas MD-87 is one of the latest small airliners of McDonnell Douglas (Now taken over by Boeing, the successor is the MD-90. After that one comes the Boeing 717). His predecessors are MD-80, MD-81, MD-82, MD-83 and MD-88. They all look very much alike, but they all have there own different accommodations and dimensions.
Avianco is a small Spanish airline with a few international destinations, namely London-Stansted and Paris, but it also flies on Heathrow, because that's where this picture is taken.