As if owning an airplane doesn’t entail enough surprises, hundreds of Lake Amphibian owners have received not-so-friendly letters from a patent enforcement company demanding money for an AD-required part that happens to be protected by a patent.

The AD requires a kit of parts to re-enforce the wing spar and was developed by Lake to fix a defect in the airplane. But as is often the case, a competing company developed a cheaper fix and Lake owners naturally availed themselves of a way to save a few bucks. …