At that time, the Lewis would have been common in .30 caliber for air service. The US had very few MGs in inventory upon its entry into the war in 1917, most of which were obsolete, so US forces didn’t have many US-made MGs available to them during WWI for either air or ground service. Therefore, they had rely largely upon French MGs (and also French artillery and aircraft). MG production was started in the US, but the war ended before very many MGs made it across the Atlantic. The US version of the Lewis Gun was made by Savage, and had been manufactured here since before the US entered the war.
My late father-in-law was a WWI pilot (though the war ended before he made it to France) and his letters of that time indicated that all of his training experience was with the Lewis Gun (he wrote some fairly detailed letters home). I even have his instruction manual for the Lewis Gun, which is well-used and not in very good condition. Of course, many different MGs in other calibers were used on French, British, and German aircraft.
By the way, the air and ground versions of the Lewis Gun were mechanically the same, but the air version had no wooden buttstock or barrel radiator jacket, and used a larger-capacity magazine.