I live in Santa Monica where many airliners join the downwind leg of the LAX pattern.
Today I witnessed what looked like a 757, joining the pattern, still a few thousand feet ASL at least, with a distinct, persistent "trail" emanating from the tail, which dissipated quickly
So - what was I seeing?
I understand that an A/C may jetison fuel if it needs to land (due to a technical issue, or medical emergency) when it has not yet burned most of it's fuel, but I don't know if fuel dumping is common practice when a regular flight comes to an end since the A/C probably has only a fraction of it's original fuel load by this time.
Or is this trail the on-board generator being started up while the A/C is still in flight, and so it's creating a bit of smoke?
I've noticed these little trails at descending altitudes before, but I find it hard to believe that airlines habitually dump fuel towards the end of a scheduled flight when they calculate so carefully how much they need.
I'm just trying to understand what it is I saw. Does the tail end of certain A/C create a visible, condensation-type vortice under certain conditions, such as the ones seen emanating from wingtips during high angles of attack in humid conditions?
Thanks in advance for your ideas.
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RE: Is Fuel Dump Before Landing Common?
Fuel dumpring is by no means a routine procedure (not with Jet-A at $2.00 a gallon!), and is only done in emergencies. Not all that many aircraft types are even equipped with a fuel dump system...
Check out: http://en.wikipedia.org/wiki/Fuel_dumping
What you probably saw was moisture. There are some pictures of it at the above link.
Check out: http://en.wikipedia.org/wiki/Fuel_dumping
What you probably saw was moisture. There are some pictures of it at the above link.
RE: Is Fuel Dump Before Landing Common?
Fuel dumping is not common. It is an abnormal procedure used to reduce the weight of the aircraft to something below its maximum landing weight.
If the vapor trail you saw was coming from the tail, it was probably the contrail from the APU exhaust.
If the vapor trail you saw was coming from the tail, it was probably the contrail from the APU exhaust.
RE: Is Fuel Dump Before Landing Common?
Plus, regular fuel dumping tends to irritate the environmentalist!
I'd second the APU... I can't think of anything else that would leave a moisture trail from the tail
I'd second the APU... I can't think of anything else that would leave a moisture trail from the tail
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- Starlionblue
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RE: Is Fuel Dump Before Landing Common?
AS OPNLGuy already mentioned, not all aircraft can dump fuel.
Given that it is such a media friendly concept, many members of the public misunderstand it greatly.
A couple of points.
- ANY aircraft can land at max takeoff weight. However in many emergencies it is safer to burn off or dump fuel in order to reduce landing speed and weight. This is especially true for long haulers that have such a high proportion of weight as fuel. An overweight landing is feasible, but more risky, and a check needs to be performed after it.
- Given the above, if the aircraft is on fire or otherwise about to fall out of the sky, it is unwise to fly around dumping fuel, even if over max landing weight.
Given that it is such a media friendly concept, many members of the public misunderstand it greatly.
A couple of points.
- ANY aircraft can land at max takeoff weight. However in many emergencies it is safer to burn off or dump fuel in order to reduce landing speed and weight. This is especially true for long haulers that have such a high proportion of weight as fuel. An overweight landing is feasible, but more risky, and a check needs to be performed after it.
- Given the above, if the aircraft is on fire or otherwise about to fall out of the sky, it is unwise to fly around dumping fuel, even if over max landing weight.
RE: Is Fuel Dump Before Landing Common?
| Quoting Dw747400 (Reply 3): Plus, regular fuel dumping tends to irritate the environmentalist! |
As I understand it, doesn't most of the fuel "harmlessly" vaporize before reaching the ground?
And I know that there is nothing "harmless" about Jet-A vapor, I used to pump the stuff...but at least it doesn't reach ground level in liquid form
Nature will take care of both Jet-A and diesel...there are naturally occurring bacteria which will digest both (in the absence of powerful and carcinogenic biocides like Prist...), however I would not want to see either fuel type introduced into the environment. I think liquid fuels do the most damage to the water table if absorbed into the soil (I took an environmental engineering class in college
).RE: Is Fuel Dump Before Landing Common?
| Quoting Fr8Mech (Reply 2): If the vapor trail you saw was coming from the tail, it was probably the contrail from the APU exhaust. |
A contrail? A couple thousand feet of the ground? I know it's possible, but certainly not in L.A. weather, maybe in Antartica and even there it is a rare ocurrence. Plus, the main engines would have been producing a contrail too.
Unless it was a chemtrail...
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- futurecaptain
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RE: Is Fuel Dump Before Landing Common?
Of course it was the lavatory dump system. The switch is on the panel next to the chemtrail generator and missile launch system.
RE: Is Fuel Dump Before Landing Common?
The 757's APU can be started in flight up to the 42000 feet service ceiling of the aircraft.
You could have seen a contrail from this apu exhaust, although, normally it would not be operated in flight.
More likely you saw moisture from a rear drain mast freeze instantly into a mini 'contrail'
In any case the 757 cannot jettison or dump fuel, the 767 can, but these dump nozzles are towards the end of each wing.
[Edited 2007-03-07 22:08:08]
You could have seen a contrail from this apu exhaust, although, normally it would not be operated in flight.
More likely you saw moisture from a rear drain mast freeze instantly into a mini 'contrail'
In any case the 757 cannot jettison or dump fuel, the 767 can, but these dump nozzles are towards the end of each wing.
[Edited 2007-03-07 22:08:08]
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- airfoilsguy
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RE: Is Fuel Dump Before Landing Common?
| Quoting KELPkid (Reply 5): As I understand it, doesn't most of the fuel "harmlessly" vaporize before reaching the ground? |
It may vaporise but the elements are still released into the air and that is what the eco Nazis don't like.
Correct me if I am wrong but don't most airliners that have the ability to dumb fuel do so by nozzles mounted on the wings and not the tail. It would only make sense to mount fuel dump nozzles closest to the main tanks.
I am guessing you probably say condensation trails.
Photo © Jean - AirTeamImages
Photo © Rez Manzoori - FlightLineImages
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- sstsomeday
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RE: Is Fuel Dump Before Landing Common?
| Quoting OPNLguy (Reply 1): What you probably saw was moisture. |
Where would the moisture come from at the end of the flight?
| Quoting Fr8Mech (Reply 2): If the vapor trail you saw was coming from the tail, it was probably the contrail from the APU exhaust. |
This is what I suspect; exhaust smoke, So I am thingking, therefore the APU was being started up when I saw the A/C, and that during it's initial ignition you can see a bit of smoke? I didn't realize they started them up while still in flight.
| Quoting FLY2HMO (Reply 7): A contrail? A couple thousand feet of the ground? |
I think he meant a trail of smoke.
| Quoting Max Q (Reply 10): More likely you saw moisture from a rear drain mast freeze instantly into a mini 'contrail' |
The A/C was too low to be in freezing air, though.
I was also thinking perhaps the kind of vapor trail you see from wingtips close to landing, when the angle of attack is high and vortices create instant little troughs of low pressure and therefore condensation. But this was from the tail, the aft tip of the fuselage, to be exact, so I wasn't aware of any structure at the tail that would create such a contrail, because that would indicate drag and inefficiency, in my way of thinking, while still in the pattern...
Thanks for all your ideas. I'm surprised an expert hasn't stepped up to state unequivocally what is was that I saw...
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- Starlionblue
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RE: Is Fuel Dump Before Landing Common?
| Quoting SSTsomeday (Reply 12): Where would the moisture come from at the end of the flight? |
In the atmosphere itself... You won't see such a thing occur someplace like PHX very often (dry air), but given that LAX is next to that big ocean thingie out to the west, LAX sees moisture-laden air all the time...
 Photo © Paul Markman |  Photo © Stuart Haigh - topjetpix |
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- futurecaptain
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RE: Is Fuel Dump Before Landing Common?
| Quoting Airfoilsguy (Reply 11): Correct me if I am wrong but don't most airliners that have the ability to dumb fuel do so by nozzles mounted on the wings and not the tail. It would only make sense to mount fuel dump nozzles closest to the main tanks. |
No, most airliners do not have the ability to dump fuel. But in an emergency all aircraft can land at max weight without dumping anything, although the plane will require a check afterward.
Basically, the ability to dump fuel isn't really needed except for the biggest planes.
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- Starlionblue
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RE: Is Fuel Dump Before Landing Common?
| Quoting Futurecaptain (Reply 16): Basically, the ability to dump fuel isn't really needed except for the biggest planes. |
Indeed. And this is because it would take so long to burn off enough fuel on long haulers with such a large fraction of weight made up of fuel.
Remember the JetBlue 32x with the transversal nose gear at LAX? Circled for 2 hours burning off fuel IIRC. Try that in a 777 loaded for Narita and you're circling for 7-8 hours at least. Fuel dumping kit starts to be worth mounting at this point.
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- citationjet
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RE: Is Fuel Dump Before Landing Common?
| Quoting Futurecaptain (Reply 16): No, most airliners do not have the ability to dump fuel. |
| Quoting Max Q (Reply 10): In any case the 757 cannot jettison or dump fuel, the 767 can |
According to Boeing Website the following aircraft have fuel jettison capability:
http://www.boeing.com/commercial/airports/faqs/fueldump.pdf
707 - yes
717 - no
720 - yes
727 - yes
737 - no
BBJ - no
747 - yes
757 - no
767-200/300 - **
767-400 - yes
777 - yes
787 - yes
DC-8 - yes
DC-10 - yes
MD-11 - yes
MD-80 - no
MD-90 - no
** Early models did not have fuel jettison capability, although airlines could install capability. Later models had jettison capability.
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- sstsomeday
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RE: Is Fuel Dump Before Landing Common?
| Quoting OPNLguy (Reply 14): Quoting SSTsomeday (Reply 12):Where would the moisture come from at the end of the flight? In the atmosphere itself... You won't see such a thing occur someplace like PHX very often (dry air), but given that LAX is next to that big ocean thingie out to the west, LAX sees moisture-laden air all the time... |
Thanks - but this was not from an area of the plane that creates any lift, therefore drag, therefore vortices, if I understand vortices correctly.
Most likely smoke from the APU unit being started up (therefore the smoke) because they do not create smoke while running on the ground. Plus there was nothing visible emanating from the engines, so it was not a "contrail."
Hmmm... a mystery.
RE: Is Fuel Dump Before Landing Common?
| Quoting SSTsomeday (Reply 19): Most likely smoke from the APU unit being started up (therefore the smoke) because they do not create smoke while running on the ground |
Are you talking about APU.On the contarary if theres an bearing Oil leak.
regds
MEL
RE: Is Fuel Dump Before Landing Common?
An APU smoking on the ground is a bad APU.
The only 'smoke' you may see from a good APU is fuel vapor at intial start-up, maybe a puff.
You probably saw a contrail from the APU exhaust, nothing more, nothing less.
The only 'smoke' you may see from a good APU is fuel vapor at intial start-up, maybe a puff.
You probably saw a contrail from the APU exhaust, nothing more, nothing less.
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- airfoilsguy
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RE: Is Fuel Dump Before Landing Common?
| Quoting Futurecaptain (Reply 16): No, most airliners do not have the ability to dump fuel. But in an emergency all aircraft can land at max weight without dumping anything, although the plane will require a check afterward. Basically, the ability to dump fuel isn't really needed except for the biggest planes. |
Try again, this time read slower.
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- futurecaptain
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RE: Is Fuel Dump Before Landing Common?
| Quoting Airfoilsguy (Reply 22): Try again, this time read slower. |
Urg. Sorry about that, I forgot how to do simple things like read when I learned how to fly planes.
My bad.
Please disregard my previous post, I need some sleep.
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- Valkyrie01
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RE: Is Fuel Dump Before Landing Common?
How about when starting the APU when it is really cold you see a few puff and more
RE: Is Fuel Dump Before Landing Common?
| Quoting Valkyrie01 (Reply 24): How about when starting the APU when it is really cold you see a few puff and more |
Yes, a few puffs can be seen at startup in cold conditions, but not enough to be mistaken as a contrail.
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