Description

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 colour of the disinfectant. Airlines are not allowed to dump their waste tanks mid-flight, and pilots have no mechanism by which to do so. However, leaks sometimes do occur from a plane's septic tank.

Third party on the ground risk

Although rare, incidents of blue ice detaching from aircraft, typically under the approach path as the mass warms sufficiently to detach from the aircraft during the descent, pose a risk to people and property (there were 27 documented incidents of blue ice impacts in the USA between 1979 and 2003). 

Danger to aircraft in flight

Historically, there have been cases of blue ice detaching from aircraft in flight and causing damage to the aircraft concerned, typically to rear mounted engines such as on the B727.