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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.

Tyler Durden
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    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. – Ron Beyer Jan 05 '17 at 04:20
  • @RonBeyer Looks like you have an answer, why limit that to a comment? – KorvinStarmast Jan 05 '17 at 05:29
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    @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. – Ron Beyer Jan 05 '17 at 05:35
  • @RonBeyer There was a thread on PPRuNe recently that had some discussion of this particular issue. I'll see if I can find it. – KorvinStarmast Jan 05 '17 at 05:39
  • 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. – mins Jan 05 '17 at 06:46
  • @RonBeyer I thought that was a malfunction with the 727, not an intentional ability? – reirab Jan 05 '17 at 07:45
  • I thought airlines pooped over the ocean. Maybe the pilot didn't want to pollute the ocean. I wonder if the poop system on airliners is automatic or manually done. – user6035379 Jan 05 '17 at 09:33
  • @user6035379 You thought wrongly. There is no "poop system" in the sense that you seem to be using the phase. – David Richerby Jan 05 '17 at 23:22
  • This question is about blue ice, not pee. – Tyler Durden Jan 05 '17 at 23:52

1 Answers1

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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

Tyler Durden
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  • 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. – J W Jan 05 '17 at 13:23
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    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. – J W Jan 05 '17 at 16:28
  • @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. – reirab Jan 05 '17 at 18:54
  • @reirab The overflow drain is only opened when the combination fill/overflow valve is opened. Overflow would only occur from over-servicing on the ground. In normal flight operation the potable water tank is pressurized by bleed air with the only open outlet being the plumbing to the faucets. Theoretically, a valve failure accompanied by some combination of a series of negative and positive G loading or excessive tank pressurization might lead to minimal dumping overboard in flight, but such a scenario would be a highly unlikely, if possible at all. – J W Jan 05 '17 at 21:11
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    @JonathanWalters If the tank is full, it will overflow. It is that simple. – Tyler Durden Jan 05 '17 at 22:08
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    @TylerDurden Where will it overflow to? The lav floor? Where will it overflow from? – J W Jan 05 '17 at 22:21