Re: Aircraft Toilets

From:         Tony Blades <>
Organization: None
Date:         12 May 95 03:22:51 
References:   1
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> My girlfriend does not believe me when I tell her that certain older,
> currently flying airliners deposit their sanitary waste out of the back
> of the aircraft during flight. Which leads to the phenomenon known as
> 'blue ice'.
> Please could someone inform me of types of aircraft which do this, as
> this matter is currently forming a bet for a dinner!

I hope that you haven't placed any bets yet as you are onto to a
sure loser.

I've been flying professionally for almost 30 years, the oldest
type being DC-4s and my current types B737-300, 400 & 500.

No aircraft that I know of dump toilet waste in flight.  Water from
wash basins is vented overboard but the contents on the toilet
holding tanks are very definately not.  Toilet waste is dumped via
a special adapter into toilet waste trucks that service the aircraft.
The holding tanks are accessed via a panel beneath which is a rubber
sealed flap.  After the discharge pipe is connected a dump toggle
is either pulled or turned, depending on the type, opening a gate
valve in the discharge duct.  Once the contents have been downloaded,
the toilet resevoir is then charged with fluid with is a mixture
of fresh water and 'Toilet Blue'.  This is a chemical substance
which is blue in colour and is designed to deduce the odour eminating
from the toilet contents after use. A similar chemical is used in
caravan and boat toilets.

If the gate valve is not properly closed, and if the seal on the
outer flap is not watertight, then the blue fluid in the toilet
holding tank can seep out past the access panel. With the very low
temperatures experienced in flight this fluid seepage freezes on
the outside of the fuselage and eventually breaks off as chunks of
'blue ice'.  These chunks of ice can in fact cause serious damage
to rear mounted engines.

I trust that this is of some help!

Tony Blades