In aviation, blue ice is frozen sewage material that has leaked mid-flight from commercial aircraft lavatory waste systems. It is a mixture of human biowaste and liquid disinfectant that freezes at high altitude. The name comes from the blue color of the disinfectant. Airlines are not allowed to dump their waste tanks mid-flight, and pilots have no mechanism by which to do so;[1] however, leaks sometimes do occur from a plane's septic tank.
There were at least 27 documented incidents of blue ice impacts in the United States between 1979 and 2003.[2] These incidents typically happen under airport landing paths as the mass warms sufficiently to detach from the plane during its descent. A rare incident of falling blue ice causing damage to the roof of a home was reported on October 20, 2006 in Chino, California.[3] A similar incident was reported in Leicester, UK, in 2007.[4]
Other documented incidents include:
Blue ice can also be dangerous to the aircraft itself — the National Transportation Safety Board has recorded three very similar incidents where waste from lavatories caused damage to the leaking aircraft,[10][11][12] all involving Boeing 727s. In all three cases, waste from a leaking lavatory hit one of the three engines the 727 has mounted in the rear, causing a power loss.[10][11][12] The flights made safe emergency landings with the two remaining functioning engines; nobody was injured. Only one report specifically mentions ice,[11] while another mentions "soft body FOD" (foreign object damage),[12] indicating that the damage was caused by a relatively soft object like a bird, or even ice, as opposed to (for example) a stone or an object made of metal.