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I had always assumed that human waste was removed from commercial aircraft while they were on the ground, some inscrutable machine coming by to suck the material out and carry it away.

Although that may happen, it appears that planes do have the ability to poop and they use that ability as one woman found out yesterday after a plane pooped on her house.

Apparently commercial carriers euphemistically call the poop "blue ice".

Under what circumstances do planes eject blue ice while airborne rather than dispose of it when on the ground?

Note that the alleged duplicate question does not answer the question correctly so I have posted a correct answer here below.

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    $\begingroup$ It is almost always the result of a leakage in the treatment system, no aircraft that I know of has the ability to purposely discharge the waste system. $\endgroup$ – Ron Beyer Jan 5 '17 at 4:20
  • $\begingroup$ @RonBeyer Looks like you have an answer, why limit that to a comment? $\endgroup$ – KorvinStarmast Jan 5 '17 at 5:29
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    $\begingroup$ @KorvinStarmast It's the "that I know of" that keeps me from that, apparently there were some 727's that had this ability. I don't know of any modern aircraft that has this "ability", but I could be mistaken, and haven't really looked into it enough to constitute a factual answer. $\endgroup$ – Ron Beyer Jan 5 '17 at 5:35
  • $\begingroup$ @RonBeyer There was a thread on PPRuNe recently that had some discussion of this particular issue. I'll see if I can find it. $\endgroup$ – KorvinStarmast Jan 5 '17 at 5:39
  • $\begingroup$ This schematic of the B737NG water/waste system can be found in this question. Waste tank collects and store toilet waste, including flush water, and is emptied only on the ground. Vacuum is created by a pump protected by a water separator and a filter. There could be a malfunction at this level. $\endgroup$ – mins Jan 5 '17 at 6:46
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After some research I discovered that "blue ice" jetsam from commercial planes are not uncommon and in several instances people have even been struck by poo bombs, although apparently noone has been killed yet.

Normally, the septic tank on a plane is evacuated on the ground by a special truck after the plane has landed. However, the septic tanks have an overflow valve. If, for any reason, the septic tank becomes full and pressurized, then it will start to overflow outside of the plane through the waste drain valve assembly (shown in diagram below). This overflow can accumulate into a ball of ice due to the freezing cold temperatures at high altitudes. The ice then falls off either when it gets too big or when the temperatures warm it as the plane nears the ground.

enter image description here

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  • $\begingroup$ This answer would be more authoritative if you were able to provide documentation for your statements regarding the overflow vent and the tank system. Such documentation should define the type of aircraft discussed as well include such information as the system's operating description and schematic. $\endgroup$ – J Walters Jan 5 '17 at 13:23
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    $\begingroup$ I studied the my maintenance manual for one of the older B737 models and it does not have an overflow valve from the waste water system. There is, however, an overflow valve from the potable water system which would dump overflow water overboard. In the absence of any evidence to the contrary I am going to suggest that you are confusing the two systems. $\endgroup$ – J Walters Jan 5 '17 at 16:28
  • $\begingroup$ @JonathanWalters Out of curiosity, what could cause the potable water system to overflow during flight? It seems like that would only be possible when filling it on the ground. $\endgroup$ – reirab Jan 5 '17 at 18:54
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    $\begingroup$ @JonathanWalters If the tank is full, it will overflow. It is that simple. $\endgroup$ – Tyler Durden Jan 5 '17 at 22:08
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    $\begingroup$ @TylerDurden Where will it overflow to? The lav floor? Where will it overflow from? $\endgroup$ – J Walters Jan 5 '17 at 22:21

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