Factual error: Doug Masters and his friend Reggie would be grounded on the spot and have their pilot's licences suspended (and in all likelihood cancelled) after buzzing the motorcyclist. Their flying is grossly unsafe. They would be visible for miles flying well below a safe altitude, but even if they were not seen their radio traffic and radar tracking would tell the authorities everything they needed to know.
Factual error: Calendar date at the very beginning of the film (in the police station), shows the dates of Saturday 20th/Sunday 21st July 1983. However the 20th and 21st July 1983 fell on Wednesday and Thursday.
Factual error: Bunny bites an aluminum beer can in half. Beer cans weren't aluminum until the mid 70s. He would have hurt his mouth on that one.
Factual error: The aircraft are definitely post-WWI. Biggles is flying a De Havilland Tiger Moth, which appeared in 1930s. The German fighter is probably the PT-23 Stearman.