14 CFR § 25.239

For seaplanes and amphibians, during takeoff, taxiing, and landing, and in the conditions set forth in paragraph (b) of this section, there may be no—

Spray characteristics that would impair the pilot's view, cause damage, or result in the taking in of an undue quantity of water;

Dangerously uncontrollable porpoising, bounding, or swinging tendency; or

Immersion of auxiliary floats or sponsons, wing tips, propeller blades, or other parts not designed to withstand the resulting water loads.

Compliance with the requirements of paragraph (a) of this section must be shown—

In water conditions, from smooth to the most adverse condition established in accordance with § 25.231;

In wind and cross-wind velocities, water currents, and associated waves and swells that may reasonably be expected in operation on water;

At speeds that may reasonably be expected in operation on water;

With sudden failure of the critical engine at any time while on water; and

At each weight and center of gravity position, relevant to each operating condition, within the range of loading conditions for which certification is requested.

In the water conditions of paragraph (b) of this section, and in the corresponding wind conditions, the seaplane or amphibian must be able to drift for five minutes with engines inoperative, aided, if necessary, by a sea anchor.