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Lavatory Economics Question  
User currently offlineflylku From United States of America, joined Apr 2006, 943 posts, RR: 0
Posted (3 years 1 month 1 week 3 days 2 hours ago) and read 20700 times:

Recently I was on an early UA 757 that has the old chemical flush commode. It struck me that when the aircraft went in for heavy maintenance there should be a real savings to replacing these with the more modern high pressure low flow commode.

The new technology should be lighter (less fluid), take up less space, and I suspect is simpler thus requiring less maintenance. Over time there should be a significant ROI to replacing the old commodes.

But of course with aviation there is always a catch and I am curious what that catch is.

- Is it technically feasible to replace them?
- If it is, is there a savings to doing so?
- If there is, is there a regulatory issue (certification)?

Has any carrier done it?

...are we there yet?
3 replies: All unread, jump to last
User currently offlinecornutt From United States of America, joined Jan 2013, 338 posts, RR: 0
Reply 1, posted (3 years 1 month 1 week 3 days 2 hours ago) and read 20701 times:

I know that on the newer Boeings, those rely on a central vacuum system that is installed at manufacture. (A side benefit is that it allows operators to move the heads and galleys around.) I assume it would be a major job to retrofit an older a/c with the vacuum system.

User currently offlineFlyHossD From United States of America, joined Nov 2009, 1409 posts, RR: 1
Reply 2, posted (3 years 1 month 1 week 3 days ago) and read 20660 times:

Quoting flylku (Thread starter):

Recently I was on an early UA 757 that has the old chemical flush commode

I suspect the cost of the change wouldn't be recovered before the plane is retired from UAL.

My statements do not represent my former employer or my current employer and are my opinions only.
User currently offlineRoseflyer From United States of America, joined Feb 2004, 11166 posts, RR: 52
Reply 3, posted (3 years 1 month 1 week 2 days 23 hours ago) and read 20605 times:

I think the reason it isn't being done is cost. Every modification has to have a payback. It is easier to justify modifications to improve dispatch reliability or improve customer satisfaction, than ones to marginally improve fuel burn through weight savings.

Re-plumbing all the lavatories is a massive undertaking. Replacing all the blue water lines with vacuum tubes is an extensive modification that requires taking the whole interior if the airplane apart. Water and waste lines running the length of the fuselage require taking a large amount of stuff off the airplane to access.

The vacuum system is centralized, so the cargo compartment waste tanks need to be replaced which again is a significant modification. The weight savings from the waste water is partially offset by the vacuum system.

As for certification, you are going to have to find someone to create the new system and certify it. It is expensive, but doable. Boeing will do it, but they are extremely expensive. Few airlines have the in house engineering staff to get such a modification approved. It is definitely doable, but expensive.

If you have never designed an airplane part before, let the real designers do the work!
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