A system for enhanced lateral stability of an amphibious aircraft includes a buoyancy system laterally displaced from opposite sides of the fuselage of the aircraft and wingtip system having a hydrodynamic planing surface associated with each wingtip. The hydrodynamic planing surface on each wingtip prevents the submersion of an associated buoyancy structure. By supplementing the lateral stability of the buoyancy structures using hydrodynamic planing surfaces, the combined lateral width of the fuselage and buoyancy structures can be reduced without detrimentally impacting operational performance. This reduced lateral width enables the amphibious aircraft to be configured for storage and transportation on a trailer or shipping container.