JRC is correct. A amphibous vehicle is technically a boat when in the water. Once on land or air it follows plane/car rules and regulations. That is why amphibous vehicles have to have all the safety equipment set forth by the CG/Dept of Safety. Trouble is the MP will have a tough time catching them once they are in the air!!!!
A Lake Amphib does not get airborne until they reach about 60 mph.