.... However, what is notable is that the FAA's 250-gram rule implicitly recognized the limits of its jurisdiction. An FAA spokesman told The Register that the 250 grams was arrived at by assuming what weight would be the lowest acceptable for a drone falling from 400 feet.

Why 400 feet? Because that is the altitude at which the FAA has a solid claim of jurisdiction. Model aircraft guidelines – over which the FAA does not have authority – cover aircraft below 400 feet and more than three miles from an airport.

Despite this calculation, the FAA does not formally accept the 400-foot jurisdiction and in fact claims this rule is a "misperception that may originate with the idea that manned aircraft generally must stay at least 500 feet above the ground." It claims authority over all airspace from the ground up – despite the fact that local law courts have repeatedly ruled otherwise.

In the only federally decided case – carried out by the Supreme Court in 1946 – it was agreed that 83 feet was the distance under which a landowner can claim jurisdiction. That same case also reinforced the 500-foot aircraft ruling....