Complex sentence: The actual date of Watson's first powered flight has not been fully established, some evidence seems to point out that the flight could not have been earlier that 1910 as his second aircraft, powered by a 30 hp Humber, was produced that year.
Split into simpler sentences: The actual date of Watson's first powered flight has not been fully established. Some evidence seems to point out that the flight could not have been earlier that 1910 as his second aircraft, powered by a 30 hp Humber engine, was produced that year.