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CF104

Dumping fuel

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I spent the weekend in the Rockies west of Denver. The cabin I was at was in the approach path for DEN so I got to see quite a few planes passing overhead.Some of the heavies I observed (767 and 777) appeared to do what I percieved to be a fuel dump while descending.While I assume this is due to landing at a higher altitude airport along with favorable winds giving them better than expected fuel performance, perhaps someone else could enlighten me on whether this is common practice or not. It appeared to me almost every plane that had fuel dump capabilities was doing it.

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I doubt very, very much whether what you saw was fuel dumping. There is absolutely no reason for fuel dumping unless in emergency and environmental authorities would be up in arms if this was a routine procedure .. and airlines don't want to waste (very) expensive fuel. And if they really were duming fuel most likely you wold not see anything - fuel is clear.Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

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Fair enough, what other possibilities then would I see a short period of contrail through the tail cone then? I personally cannot think of anything else, unless they are starting the APU perhaps that could cause this.

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I can say for certain that it was not fuel dumping. I lived in Colorado almost all of my life so I know how most of the environmentalists are out there, and trust me if one plane did a fuel dump over the mountains they would have that airline shut down! :-) Maybe someone more qualified than I can answer but I can not see any scenario where a plane could have enough fuel savings on one flight to necessitate dumping fuel upon reaching it's destination. The airlines really watch every penny so they figure the numbers pretty tight. Now to answer your question, what was it? Well if I remember correctly at one time here in the forums Dark Moment (pretty sure it was him, I hope!) "argued" about this, they were dumping the latrines. See Mark I told you they dump the latrines in flight! :-lol I am joking of course! I am pretty sure, like the others that it was the APU start up that you were seeing. To my knowledge that is the only thing that would appear from the nose cone area. Anyway how did you like Colorado? Was this your first trip? Why did you not take me along? :-)Take care,Philip Olsonhttp://www.precisionmanuals.com/images/forum/supporter.jpg

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For what it is worth my educated guess is that you may have seen a contrail or condensation generated by either an apu intake door being open or something similiar. The odd thing is that it comes from the tailcone instead of the wings or flap-edges.You will see the small trail of condensation (or contrail) on the flap edges where the vortex creates a low pressure region and the water condenses out in thin white streamers. You'll also see this when a fighter gives an airshow display pulling high G's. Of course it has to be on a humid day.I doubt the two man crew would initiate an APU start during the critical phase of the approach. That is a distraction and probably against airline policy to do on short final. Also with the way planes "plug-in" at the gate running the APU costs money...though there may have been an operational need to.Tim

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Actually the original post said he was in the mountains west of Denver. Not really a 'short final' situation. ;-) Regardless, depending on the operator, many larger aircraft have the APU start up as part of their approach check list. This is to provide a backup generator source in case of an engine failure on final. This is really only critical in a CatII or III situation where the AC buses require split power sources but it is standard with some operators.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

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Actually the "approach checklist" is not accomplished while on the approach--you are doing it WAY too late at that point. You are all ready into the SMAC and SOPA to go messing about trying to configure your a/c. Of course there is that age-old arguement whether a checklist is a "Check" or a "Do" list. Depends who you are flying for. The APU has to be established, on line and available prior to starting the approach-you can't go past the item until it is completed and available, you'd chew up a lot of air waiting for that puppy to spool-up in a high-workload regime.Normally if we are within parameters I'll have it started(if needed) while I am doing the approach brief prior to getting into the terminal environment if we are not anticipating a delay. Also because it is on the checklist does not mean it has to be done if it is an "As Required" item. Majority of the time it isn't required since I am visual anyway from the OM inbound. Cat II/III in real world don't happen that much in CONUS.Tim__757

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Don't know where I said anything about the approach checklist being done "on the approach"?! Just pointed out that if he was in the mountains west of Denver, they're not on short final. At this point they were probably getting into terminal, not final. Don't have a chart handy at the moment. There are several overseas operators into Denver as well and they also operate the APU on approach, if required, and some are manditory regardless of weather.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

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