The present invention provides an aircraft buoyancy system (14) for providing positive buoyancy to an aircraft (15) to keep it afloat at the surface of a body of water (16) after crashing, ditching or landing into a body of water (16). The aircraft buoyancy system (14) comprises at least one inflatable body (1) which, when inflated, increases the buoyancy of the aircraft (14), and a gas generation system (4) to inflate the at least one inflatable body (1). The aircraft buoyancy system (14) also comprises a sensor and activation system (3) to activate the gas generation system (4). Upon activation of the sensor and activation system (3) the gas generation system (4) causes a gas to flow to the at least one inflatable body (1), causing the aircraft (15) to float and remain at the surface of a body of water (16).