# Spinoff from emergency plane landing threads **URL:** \ **Category:** Factual Questions\ **Created:** [October 20, 2013, 2:57am UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701 "2013-10-20T02:57:10Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [October 20, 2013, 2:57am UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/1 "2013-10-20T02:57:10Z")
Question: When a plane dumps fuel at a low altitude, would people and objects on the ground get sprayed, or at least feel it, or does it usually evaporate before it hits the ground. Don’t need the answer any time soon. 😃 Also, I saw two vapor trails “cross” several days ago. I realize the planes might have been several miles apart, but it was really freaky to see that. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [October 20, 2013, 3:46am UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/2 "2013-10-20T03:46:47Z")
> [@nearwildheaven](#): > > **Also, I saw two vapor trails “cross” several days ago.** I realize the planes might have been several miles apart, but it was really freaky to see that. :eek: !!! They crossed the streams??? _Don’t cross the streams!_ > [@](#): > > ``` > Egon Spengler: There's something very important I forgot to tell you. > Peter Venkman: What? > Spengler: Don't cross the streams. > Venkman: Why? > Spengler: It would be bad. > Venkman: I'm fuzzy on the whole good/bad thing. What do you mean, "bad"? > Spengler: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light. > Ray Stantz: Total protonic reversal. > > ``` (From [Wiki](http://en.wikiquote.org/wiki/Ghostbusters) article.) ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [October 20, 2013, 4:18am UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/3 "2013-10-20T04:18:29Z")
Gas? 100LL? Auto fuel in an app-roved aircraft engine? Jet A? Jet A w/prist? What kind of plane? KC-135 tanker will take a while depending … Bonus question: Is it circling? How tight? How long? ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [October 20, 2013, 3:48pm UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/4 "2013-10-20T15:48:50Z")
It wasn’t so much that the vapor trails crossed, but that the planes appeared to be heading straight for each other, and did indeed “meet” from my vantage point. KWIM? ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 20, 2013, 9:42pm UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/5 "2013-10-20T21:42:17Z")
> [@nearwildheaven](#): > > Question: When a plane dumps fuel at a low altitude, would people and objects on the ground get sprayed, or at least feel it, or does it usually evaporate before it hits the ground. If it’s done according to regulations then it should be in an area away from people and at a high enough altitude to allow for most of it to evaporate (above 2000’ according to the FAA). If done low enough then I guess you might feel the spray. Note that small to medium sized jets such as the B737 and A320 can’t dump fuel. > [@](#): > > Also, I saw two vapor trails “cross” several days ago. I realize the planes might have been several miles apart, but it was really freaky to see that. Opposite direction traffic is separated by at least 1000 feet vertically so it’s quite likely that you saw them cross paths but there was no collision risk. ---
**Author:** ![JerrySTL](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@JerrySTL](https://boards.straightdope.com/u/JerrySTL)\ **Post date:** [October 21, 2013, 3:22pm UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/6 "2013-10-21T15:22:04Z")
I worked on an aircraft (F-111) that had the fuel dump between the exhaust of its two engines. The pilots would dump fuel and hit afterburner on occasions such as their last flight. About 100 foot of flames trailing behind the aircraft was impressive in the day and really, really impressive at night. I remember smelling the fumes after one of these displays that was close to the runway, so I guess it’s possible that you could smell fuel if it was just dumped that low. Another aircraft that I worked on , Sabreliner / T-39, had a fuel jettison system, but it only held 7,000 pounds of fuel totally filled. We would hook up a 1" ID hose (if memory serves) to the jettison pipe and pump out fuel until it automatically stopped. The idea was that the fuel dump system wouldn’t drain all the fuel while in flight - only enough to allow a safe landing. I doubt that you’d even smell the fuel if the aircraft was flying at much of any altitude. I was somewhat amazed that the DC-9-30s that I worked on didn’t have a fuel dump system. They could land with an almost maximum fuel load on board. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 21, 2013, 11:44pm UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/7 "2013-10-21T23:44:37Z")
Yes, fuel dumping systems are pretty much limited to wide-body jets. The wiki site on [fuel dumping](http://en.wikipedia.org/wiki/Fuel_dumping) has some history on the requirements for it. Essentially the current rule is that you have to have the certification performance at maximum take-off weight to do a missed approach/go around for the aircraft to not require a fuel dump system. > [@wikipedia](#): > > Longer-range twin jets such as the Boeing 767 and the Airbus A300, A310, and A330 may or may not have fuel dump systems, depending upon how the aircraft was ordered, since on some aircraft they are a customer option. Three- and four-engine jets like the Lockheed L-1011, McDonnell Douglas DC-10 / MD-11, Boeing 747 and Airbus A340 usually have difficulty meeting the requirements of FAR 25.119 near maximum structural takeoff weight, so most of those have jettison systems. A Boeing 757 has no fuel dump capability as its maximum landing weight is similar to the maximum take-off weight ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 21, 2013, 11:53pm UTC](https://boards.straightdope.com/t/spinoff-from-emergency-plane-landing-threads/671701/8 "2013-10-21T23:53:05Z")
If you don’t have fuel dump capability and you have an emergency after take-off requiring a return to land, you have two options. You either land over weight or you fly around for an hour or two until you meet your landing weight requirements. For anything but a time critical emergency, you’d burn fuel down to your landing weight. Landing weight can also be an issue on normal flights. On the short one to two sectors that we do, our take-off weight is often limited by our landing weight at the destination and if we don’t burn as much fuel en route as we expect to, we can arrive too heavy for landing. We have to keep a careful eye on our expected fuel on arrival and if necessary fly at lower levels to increase the burn or, more often, use the air brake during the descent to increase the burn. Another option is to get the gear and flap out early in the approach as the extra drag results in a higher fuel burn. As a last resort you just hold.