So what does it take for a Flight Instructor (CFI) to teach in a sea plane or amphibious airplane? Is there any special or additional training requirements? Any CFI certificate endorsement required?
The answer is simple; you are allowed to teach in any single engine airplane for which you hold pilot privileges. Your CFI certificate says – “Airplane Single Engine”. Your pilot certificate (commercial pilot) reads – “Airplane single engine land, Airplane single engine sea”. In this case you can teach in both the land and sea single engine airplanes.
In other words, if you already hold a commercial pilot and a flight instructor (CFI) certificate, and you go get a single engine sea add-on rating on your commercial pilot certificate, you are authorized to teach in a sea plane or an amphibious airplane.