It was the Lost World (1925). It was shown on an Imperial Airways flight from London to Paris in April of 1925. A promotional short called ‘Howdy Chicago’ was shown on a short flight around the city in 1921, but this was the first feature-length film.
Here’s a short silent film showing them preparing the plane for the screening of the Lost World. Enjoy!
Ben Hur has the honor of being the most expensive silent film ever made, at a whopping $3.9 million in 1925 money! Metropolis was the most expensive foreign silent film at 5 million Reichsmarks. In January of 1927 the exchange rate was 4.2 Reichsmarks to $1. So, in 1927 dollars that was about $1.19 million. Still, a whole lotta money! The General holds the record for the most expensive single scene ever shot in a silent film – $46,000 for the part where the train plunges off the burning bridge into the river.