To my knowledge, the first scheduled commercial powered flight in an airplane involving a paying passenger was on January 1st, 1914. The passenger was a man named Abram C. Pheil, who was a warehouse/commercial property owner and the former mayor of St. Petersburg, Florida. The pilot on that inaugural commercial passenger flight was early test pilot and barnstormer Tony Jannus, and the aircraft used was a two seat (actually a single side-by-side bench seat I believe) Model 14 Benoist Airboat powered by a 75-horsepower in-line, liquid cooled Roberts six-cylinder piston engine. As the aircraft's name suggests, it was an amphibious plane that took off and landed on the water.

The ticket for the flight was purchased by Abram Pheil at auction for the rather impressively large price of $400 (close to $9500 in today's money). The aircraft flew from St. Petersburg to Tampa, Florida, and then made a return trip later that same day - again with Abram Pheil as passenger and Tony Jannus at the controls (total round trip airborne time was less than 1.5 hours total). This was also the first commercial passenger flight that was forced to make an emergency landing, as on the first leg of the trip, the pilot was forced to make a landing in Tampa Bay in order to repair a misfiring engine before taking off again to complete the journey, landing in the mouth of the Hillsborough River near downtown Tampa.