Fuel Dumping
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Fuel Dumping
Hello there.
Something I've always wondered about: you hear a lot of stories about aircraft developing problems on take-off and dumping fuel for a while before returning to the airport for an emergency landing. Is this an absolute necessity or is it more in the realms of preference to land with a lighter a/c? Am I right in thinking that if you had a very pressing emergency where getting back on terra ferma was a matter of urgency - some sort of fire or hydraulic failure springs to mind - you'd just go straight back to the nearest active runway? In what circumstances do you take the time to dump fuel, and what factors influence the decision? Is weather a factor - does it become unsafe to dump fuel if there's lightning around, for example?
Thanks in advance for any enlightenment.
Something I've always wondered about: you hear a lot of stories about aircraft developing problems on take-off and dumping fuel for a while before returning to the airport for an emergency landing. Is this an absolute necessity or is it more in the realms of preference to land with a lighter a/c? Am I right in thinking that if you had a very pressing emergency where getting back on terra ferma was a matter of urgency - some sort of fire or hydraulic failure springs to mind - you'd just go straight back to the nearest active runway? In what circumstances do you take the time to dump fuel, and what factors influence the decision? Is weather a factor - does it become unsafe to dump fuel if there's lightning around, for example?
Thanks in advance for any enlightenment.
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Hi Mongolfier ,
The main reason for dumping fuel is to lighten the aircraft weight significantly from its very heavy take off weight to its safe landing weight . Failure to do this and carry out an overweight landing can cause some pretty major damage to the airframe so its prudent to get rid of a few tons of excess weight prior to landing. In the case of a major emergency ,fire etc, a landing would be performed regardless of weight etc.
I believe fuel dumping is not permitted in lightning conditions .
Hope that helps ,
regards Paul.
The main reason for dumping fuel is to lighten the aircraft weight significantly from its very heavy take off weight to its safe landing weight . Failure to do this and carry out an overweight landing can cause some pretty major damage to the airframe so its prudent to get rid of a few tons of excess weight prior to landing. In the case of a major emergency ,fire etc, a landing would be performed regardless of weight etc.
I believe fuel dumping is not permitted in lightning conditions .
Hope that helps ,
regards Paul.
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Failure to do this and carry out an overweight landing can cause some [b]pretty major damage to the airframe[\b] so its prudent to get rid of a few tons of excess weight prior to landing
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That 15 minutes assumes a suitable runway is available. If even a long runway is wet, there may not be enough of it available to stop. Then the "major damage" will be done to the airplane or other stuff on the ground after it overruns.
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That 15 minutes assumes a suitable runway is available. If even a long runway is wet, there may not be enough of it available to stop. Then the "major damage" will be done to the airplane or other stuff on the ground after it overruns.
i.e. if the RWY you left from is long enough to accelerate to V1 then either go on one less eng or stop, chances are its long enough to come back and land at the same weight given normal flight control and braking systems.
If you are in a situation that limits flap/spolier/brakes/wheels etc then either a) Its not likely to be an "immediate return to land" situation or b) It is and you haven't paid your karma tax
Most overweight landing events require minimal maintenance action provided the RoD at touch is controlled (360'/min I think is the Bus number)
In what circumstances do you take the time to dump fuel, and what factors influence the decision?
Engine failure/contained eng fire on 747 = No biggy, dump and return (or carry on across the pond in some airlines...)
Uncontrolled Cargo fire = Pucker factor 9.5 Return to land asap. Considerations are the high brake temps you will have.
Is weather a factor - does it become unsafe to dump fuel if there's lightning around, for example?
The 747 has a limit on dumping when flaps are going from 1-5 (I think - bit fuzzy now) which relates to the stream coming close to eng exhaust I believe.
Last edited by jtr; 3rd May 2010 at 01:55.
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The cargo fire is the main reason for an immediate return to land.
At max TOGW on a 744 I can take off on a wet 11,200' runway with medium braking action. The landing distance is 11,690' at 390T. One of the problems is that you can take off with flaps 20, but cannot land with flaps 30 (must use flaps 25 because of the high approach speed; flap relief will not allow them to go down to 30).
So, while in MOST circumstances you can immediately return to land, there are some relatively common circumstances where you may NOT be able to stop on the runway.
At max TOGW on a 744 I can take off on a wet 11,200' runway with medium braking action. The landing distance is 11,690' at 390T. One of the problems is that you can take off with flaps 20, but cannot land with flaps 30 (must use flaps 25 because of the high approach speed; flap relief will not allow them to go down to 30).
So, while in MOST circumstances you can immediately return to land, there are some relatively common circumstances where you may NOT be able to stop on the runway.
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Hey Intruder,
With due respect (and adding the caveat that I haven't flown it for a couple of years now so went to the manuals to check) I had a look and came up with...
390T
MED Braking Action
Nil Wind
2 Rev + 2 Rev Idle
AB Max
F25
Distance = 11,020
The company I worked for at the time used specific definitions for runway condition for take off so assuming your MED action on T/O equates to contamination of some form (i.e. the next step up from wet) I dived in and put 3mm Slush (the most "generous" contamination) and can only lift 377t off a 12,400' runway (packs off)
Applying same thing to a shorter runway with dry conditions (9,250')
TO (Packs off) 356T
Land (AB MAX) 356T only need 7,000'
So i really cant bring understand your numbers. (cue debate)
I tend to think of it in the sense that if its a go decision then the runway length is adequate to accel to V1, lose one, continue to accelerate on 3, clear the far end at screen height at V2.
Reverse the situation, returning at more of less the same speed (averaging out F25 against weight in fuel used i.e. V2 - 182 ish Vref 25 - 187ish) across the numbers at about 90-100' (slightly higher than screen height) we surely must have the ability to decelerate the A/C at a greater rate than we just accelerated it.
I have never done an RTO on a cont/med runway but when I have on a normal and wet I know for sure even at MTOW the old girl pulled up a hell of a lot quicker than I have EVER felt it accelerate AT ANY WEIGHT. Cont runway is obviously a different issue but as you know that leads to low V1's and very limited TOWs.
Sadly the charts are somewhat limited in my manual and the RTOW ones are horrendous so anything outside of Dry/Wet/Slush is a bit hard for me to look at.
The landing distance is 11,690' at 390T.
390T
MED Braking Action
Nil Wind
2 Rev + 2 Rev Idle
AB Max
F25
Distance = 11,020
The company I worked for at the time used specific definitions for runway condition for take off so assuming your MED action on T/O equates to contamination of some form (i.e. the next step up from wet) I dived in and put 3mm Slush (the most "generous" contamination) and can only lift 377t off a 12,400' runway (packs off)
Applying same thing to a shorter runway with dry conditions (9,250')
TO (Packs off) 356T
Land (AB MAX) 356T only need 7,000'
So i really cant bring understand your numbers. (cue debate)
I tend to think of it in the sense that if its a go decision then the runway length is adequate to accel to V1, lose one, continue to accelerate on 3, clear the far end at screen height at V2.
Reverse the situation, returning at more of less the same speed (averaging out F25 against weight in fuel used i.e. V2 - 182 ish Vref 25 - 187ish) across the numbers at about 90-100' (slightly higher than screen height) we surely must have the ability to decelerate the A/C at a greater rate than we just accelerated it.
I have never done an RTO on a cont/med runway but when I have on a normal and wet I know for sure even at MTOW the old girl pulled up a hell of a lot quicker than I have EVER felt it accelerate AT ANY WEIGHT. Cont runway is obviously a different issue but as you know that leads to low V1's and very limited TOWs.
Sadly the charts are somewhat limited in my manual and the RTOW ones are horrendous so anything outside of Dry/Wet/Slush is a bit hard for me to look at.
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I used the current charts for our airplanes with the CF6-80-B5F engines. I don't know what engines your airplanes had, but the takeoff performance with the B5F is significantly better than with the B1F. OTOH, I suspect landing performance is the same, since the reverse thrust difference would be almost negligible.
Remember that for an RTO the max reject speed is at V1, not V2, so there is significantly less energy to dissipate than on landing.
Also, there have been a variety of assumptions made for T/O and landing calculations over the years, so your charts may have different assumptions than ours. Add in interpolation errors, and the fact that you admit that "the charts are somewhat limited in my manual," and I don't understand why you are so adamant that "i really cant bring understand your numbers" when the difference is about 5% between yours and ours...
Remember that for an RTO the max reject speed is at V1, not V2, so there is significantly less energy to dissipate than on landing.
Also, there have been a variety of assumptions made for T/O and landing calculations over the years, so your charts may have different assumptions than ours. Add in interpolation errors, and the fact that you admit that "the charts are somewhat limited in my manual," and I don't understand why you are so adamant that "i really cant bring understand your numbers" when the difference is about 5% between yours and ours...
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Hey there, cheers for the response.
I realise higher rated engines will have an effect - For info I was using the charts for RR RB211-524 with the H-T core mod.
Absolutely, but you have also used more than half of the usable runway to get to said V1
By "somewhat limited" I mean I dont have the ability to calculate T/O performance using "Medium" as a runway penalty. I didnt know Boeing published them for anything other than "Standard" contaminants. I have only flown the 74 for 2 different companies/countries regulations but both only saw me presented with what I thought were the "standard" contaminant options i.e. Dry/Wet/Standing Water 3mm/Slush 3mm-12mm/Loose snow 3mm-48mm/Compacted Snow so it is hard to compare your T/O perf with the online calcs I can use, and I can only put the data in for ports the company operates to (well unless I was ambitious enough to go into the FCOM 2 charts and start drawing lines)
In saying I cant bring myself to understand your numbers I am trying to say that even when I lean the numbers heavily in favour of your methodology (i.e. inferring that 3mm slush equates to MED) I still get numbers that show an immediate return possible under all conditions.
I guess my intrigue springs from having departed from long/short runways heavy/light and with pretty much every possible contamination in the book I have never given more than a passing glance to an immediate return in regards to landing distance as according to the numbers we use it is never an issue. I think the engines you are using are about 62,000lb thrust vs the H-T being just under 60,000 so I guess that is where the answer lies. Interesting that such a small difference can have such a large effect on something that is quite critical when things go wrong.
Luckily
I now fly twins so dont have to worry about these things
I realise higher rated engines will have an effect - For info I was using the charts for RR RB211-524 with the H-T core mod.
Remember that for an RTO the max reject speed is at V1, not V2, so there is significantly less energy to dissipate than on landing.
By "somewhat limited" I mean I dont have the ability to calculate T/O performance using "Medium" as a runway penalty. I didnt know Boeing published them for anything other than "Standard" contaminants. I have only flown the 74 for 2 different companies/countries regulations but both only saw me presented with what I thought were the "standard" contaminant options i.e. Dry/Wet/Standing Water 3mm/Slush 3mm-12mm/Loose snow 3mm-48mm/Compacted Snow so it is hard to compare your T/O perf with the online calcs I can use, and I can only put the data in for ports the company operates to (well unless I was ambitious enough to go into the FCOM 2 charts and start drawing lines)
In saying I cant bring myself to understand your numbers I am trying to say that even when I lean the numbers heavily in favour of your methodology (i.e. inferring that 3mm slush equates to MED) I still get numbers that show an immediate return possible under all conditions.
I guess my intrigue springs from having departed from long/short runways heavy/light and with pretty much every possible contamination in the book I have never given more than a passing glance to an immediate return in regards to landing distance as according to the numbers we use it is never an issue. I think the engines you are using are about 62,000lb thrust vs the H-T being just under 60,000 so I guess that is where the answer lies. Interesting that such a small difference can have such a large effect on something that is quite critical when things go wrong.
Luckily
I now fly twins so dont have to worry about these things
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All commercial transport aircraft are certified to land within 15 minutes of taking off at maximum takeoff weight without causing "pretty major damage", this can be achieved with or without a fuel jettison system..... Look at FAR25.1001
For most large commercial airliners landing above the maximum landing weight will require an extensive "heavy/overweight" landing inspection. Therefore, it is cheaper to dump fuel tah it is to land above the max landing weight and undergo the mandatory inspection.
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I guess my intrigue springs from having departed from long/short runways heavy/light and with pretty much every possible contamination in the book I have never given more than a passing glance to an immediate return in regards to landing distance as according to the numbers we use it is never an issue. I think the engines you are using are about 62,000lb thrust vs the H-T being just under 60,000 so I guess that is where the answer lies. Interesting that such a small difference can have such a large effect on something that is quite critical when things go wrong.
Also, since we fly close to max allowable TOGW quite often, we have made it habit to check the Runway Performance Manual for all takeoffs. There are not a lot of cases where an immediate return is not possible "by the numbers," but those cases do exist. Still, it may be worth the risk to try to land anyhow in the case of a cargo fire, since an overrun (especially into EMACS) would likely be less hazardous than an uncontrolled fire airborne.
