CTRL_ALT_DEL From Ireland, joined Feb 2001, 69 posts, RR: 0 Reply 3, posted (4 years 4 months 1 week 4 days 11 hours ago) and read 4688 times:
Hi Keesje,
Maybe my eyes are deceiving me but I don't think it's coming from the APU.
It appears to be well forward of the APU on the underside of the fuselage.
The APU is most likely off in this phase of flight.
TupolevTu154 From UK - England, joined Aug 2004, 2116 posts, RR: 31 Reply 4, posted (4 years 4 months 1 week 4 days 11 hours ago) and read 4676 times:
I'm no mechanic/engineer but that's not from the APU. It wouldn't be operational at that stage of flight. And as Oly720man said, there's definitely something being vented from the aft fuselage, possibly from the galley sinks.
HT From Germany, joined May 2005, 6471 posts, RR: 27 Reply 5, posted (4 years 4 months 1 week 4 days 11 hours ago) and read 4664 times:
Quoting TupolevTu154 (Reply 4): And as Oly720man said, there's definitely something being vented from the aft fuselage, possibly from the galley sinks.
Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?
At which location of the a/c does the consumed fraction of cabin air gets blown off / released ?
Would it contain enough moisture to form visible condensation ?
-HT
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
LarSPL From Netherlands, joined Apr 2002, 466 posts, RR: 0 Reply 6, posted (4 years 4 months 1 week 4 days 10 hours ago) and read 4652 times:
the APU is usually not on, but certain operations/procedures could require the apu to be on. for example; if an engine generator is u/s it could be required.
however, in this case it looks like water from the galley or toilet sink.
Pihero From France, joined Jan 2005, 3489 posts, RR: 72 Reply 7, posted (4 years 4 months 1 week 4 days 10 hours ago) and read 4643 times:
Quoting Oly720man (Reply 2): It looks like something is venting from the bottom of the fuselage aft of the wing root fairing. There's a stream of condensation anyway.
FlyASAGuy2005 From United States of America, joined Sep 2007, 6506 posts, RR: 11 Reply 8, posted (4 years 4 months 1 week 4 days 8 hours ago) and read 4600 times:
You can tell it's not the APU. The trail is coming from well under the fuselage.
CAM2:"Lightning coming out of that one." CAM1: "What?"
TristarSteve From Sweden, joined Nov 2005, 3687 posts, RR: 34 Reply 9, posted (4 years 4 months 1 week 4 days 8 hours ago) and read 4594 times:
Quoting LarSPL (Reply 6): the APU is usually not on, but certain operations/procedures could require the apu to be on. for example; if an engine generator is u/s it could be required.
The B777 has two generators on each engine. The APU is not required for a generator failure.
Agreed. On the B777 there is a water drain valve in the line to each drain mast. It builds up a head of pressure then opens and releases a lot of water in one go.
Quoting HT (Reply 5): Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?
The B787 is the first airliner to direct grey water into the waste tank. It has no drain masts.
CTRL_ALT_DEL From Ireland, joined Feb 2001, 69 posts, RR: 0 Reply 10, posted (4 years 4 months 1 week 4 days 8 hours ago) and read 4585 times:
Interesting.
How many kgs/lbs of water typically does a 777 carry/release on a trans-Atlantic flight?
Does the use of drain masts significantly reduce fuel consumption?
Transpac787 From United States of America, joined Jul 2007, 3138 posts, RR: 14 Reply 12, posted (4 years 4 months 1 week 3 days 19 hours ago) and read 4327 times:
I'm no A&P by any means, but I do know that in some cases, a 777 *will* run the APU in flight. This past October I flew DME-ORD on an AA 777, and we were briefly delayed departing DME to get some additional fuel. In flight the captain came back and talked with my briefly (having hung out with the crew on the 2-day layover) and I asked him why we needed the additional fuel and he said because we would be running the APU the entire flight given some ETOPS restriction of some sort.
I have ~no~ idea what the restriction was - if there was an engine generator INOP or what - but I do know for a fact we ran the APU the entire flight from DME to ORD.
Soon7x7 From United States of America, joined May 2006, 2796 posts, RR: 14 Reply 13, posted (4 years 4 months 1 week 3 days 19 hours ago) and read 4296 times:
I've often wondered what is eminating from the belly area of the aircraft. I live under the JFK approach from Europe and always notice the "third stream" venting off the tail cone even though I'm aware it is originating from the belly area...thought it was those last minute rushes to the lavatory which would not bode well as when I witness this I am usually at my sailboat and this discharge occurs over the waters I play in.
Quoting TupolevTu154 (Reply 4): I'm no mechanic/engineer but that's not from the APU. It wouldn't be operational at that stage of flight.
Quoting TristarSteve (Reply 9): The B777 has two generators on each engine. The APU is not required for a generator failure.
If everything is normal, it's not required for system functions, but it certainly can be on and may have to be on in certain dispatch or ETOPS conditions.
Quoting HT (Reply 5): Is this still common on modern airliners?
Is it only the fluids from the toilets that go into the waste water tank ?
TristarSteve is right, to the best of my knowledge. Only the 787 keeps its grey water on board. All other modern airliners drop grey water out a mast, whilbe black water (toilets) is held.
Quoting HT (Reply 5): At which location of the a/c does the consumed fraction of cabin air gets blown off / released ?
Would it contain enough moisture to form visible condensation ?
It goes out at the outflow valves...the location varies by aircraft type. Cabin air is pretty dry, so I suspect it doesn't cause condensation under most conditions, even with the large temperature drop. Even if it does cause condensation, the mass flow is hugely smaller than the engines so it might not be visible from far away.
Quoting CTRL_ALT_DEL (Reply 10): Does the use of drain masts significantly reduce fuel consumption?
That's a very interesting systems design problem. You save fuel by losing the extra weight, but you burn more by dragging the drain mast through the air. I suspect the optimum solution depends a lot on both your aerodynamics, your size, and your mission profile.
Quoting Oly720man (Reply 2): It looks like something is venting from the bottom of the fuselage aft of the wing root fairing. There's a stream of condensation anyway.
This could be the Hydraulic air driven pumps which we have two of them in the 777 (left aft body fairing) and they operate as demand pumps if they needed.
Quoting TristarSteve (Reply 9): The B777 has two generators on each engine. The APU is not required for a generator failure.
True, the B777 has two generators in each engine, but one is buck up and can provide only 20 kVA for the essential loads (unlike the main generator which supply 120 kVA and the APU generator 120 kVA), so in case of one generator failure or engine failure the APU will be needed the whole flight. (the APU in B777 can provide electrical power at any altitude and pneumatic power up to 22,000 feet)
Dragon6172 From United States of America, joined Jul 2007, 1160 posts, RR: 0 Reply 18, posted (4 years 3 months 3 weeks 5 days 20 hours ago) and read 3019 times:
In the words of Cousin Eddie...."Sh@#$er was full!!"
Sponsor Message: 
From Ireland, joined Feb 2001, 69 posts, 
From , joined Dec 1969, posts, 
From United Kingdom, joined May 2004, 6177 posts, 
From UK - England, joined Aug 2004, 2116 posts, 
From Germany, joined May 2005, 6471 posts, 
From France, joined Jan 2005, 3489 posts, 
From United States of America, joined Sep 2007, 6506 posts, 
From Sweden, joined Nov 2005, 3687 posts, 
From Canada, joined Jan 2006, 12709 posts, 
From Bhutan, joined Feb 2002, 89 posts, 
From Bahrain, joined Jan 2009, 39 posts, 
Sponsor Message: 
Printer friendly format
