YVR74
Posts: 139
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Explain Dumping Fuel?

Sat Oct 12, 2002 8:34 am

I have read and heard in various places about an aircraft dumping fuel. Can someone tell me about it? Are hundreds of gallons of jet fuel just sprayed hither and yon as the airplane flies? Can this occur over land and water alike? Of course, it's a secondary consideration to the lives of passengers and crew, but is this quite damaging to the environment?

I know nothing about it, but I can't quite reconcile the image in my mind's eye of these portals on an aircraft opening up and torrential streams of fuel spewing into the air. What about rear engined aircraft such as the ERJ, CRJ, and DC9? Is there any concern about jet fuel being sucked into the front of an engine or since that's what jet engines do is burn fuel, does it not matter?
 
LY744
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 8:45 am

Smaller a/c like the CRJ and DC-9 would probably not have fuel dumping capability anyways, it's not even standard on 767s.

LY744.
Pacifism only works if EVERYBODY practices it
 
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apuneger
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 9:05 am

I heard/read somewhere that (most of?) the fuel actually evaporates before it ever touches soil or water. Can anyone confirm this please?

The 737 doesn't have fuel dumping posiibility either. It's funny to read after a Olympic Airways 737 had to make an emergency landing at BRU that the plane "dumped fuel" above the Northsea. According to other info it just burned fuel in a BUN VOR holding pattern.  Smile/happy/getting dizzy But let's stick to the topic, OK?

So, according to what I've heard/read, aircraft tend to dump fuel mostly above the sea, whenever possible (possibly to reduce the risk of fuel falling on the ground and endangering the lives of citizens?).

Interesting topic. I'd also like to know more actually  Wink/being sarcastic

Ivan
Ivan Coninx - Brussels Aviation Photography
 
covert
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 9:09 am

If fuel is dumped at high altitude it will vaporize in the atmosphere. Like the previous guy said, not all aircraft have that capability. Usually fuel is dumped in an emergency situation to get the aircraft down to landing weight. You probably still could land safely, maybe you'd put a crater on the runway and you'd stress your brakes, gear, and would probably need more length, but no big deal. Maybe if Swissair 111 didn't dump fuel they would be still around today...
none
 
OPNLguy
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 9:30 am

There have been many threads about fuel dumping, and as others have said, it enables the aircraft to get down to a lower max landing weight in the event of some circumstance where you're landing sooner than planned.

An earlier FAA reg said that if the difference between an aircraft's max takeoff weight and it's max landing weight weight was greater than 105%, a fuel dump system had to be installed. The 707, 727, and DC-8 thus required them. As shorter range aircraft (DC-9 and 737) they didn't need one. As DC-9 and 737 variants with increased range started coming out, the FAA reg with the 105% limitation was amended to now require a certain climb gradient, which given the more powerful engines that the new aircraft variants were sporting, easily met the gradient. Subsequent variants of the aircraft (especially the 737 family) also easily met the requirements.

Basically, it's older aircraft like the 707, 727, DC-8, DC-10, L-1011, and 747 that have fuel dump systems. Other newer aircraft like the 757, 767, or 757 may or may not have fuel dumping as an option.

As far as the newer 737s are concerned, they can land at their max takeoff weights, although it will require an overweight landing inspection, usually no big deal.

Some dumping pix...


View Large View Medium
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Photo © Peter D. Baumgartner
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Photo © Mike Parks



View Large View Medium
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Photo © Mulder
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Photo © Richard Zeman

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Guest

RE: Explain Dumping Fuel?

Sat Oct 12, 2002 9:42 am

Dumping fuel is done (on those aircraft which have jettison capability) to reduce the weight - either to the maximum landing weight, or further, to the lowest possible weight... the lower the weight, the lower the landing speed. Dumping fuel for a 747 classic from max takeoff weight to maximum landing weight takes some 35-40 minutes time. Fuel consumed by the operating engines during that time is included in the weight reduction computations.
xxx
Be aware that, if the emergency so dictates, airplanes can be landed at their maximum takeoff gross weight, but sometimes, this can be impossible due to short runway considerations...
xxx
If an airplane is released for flight - with an inoperative jettison system - the maximum takeoff weight may often be restricted to a weight only slightly higher to the maximum landing weight, you have to check the applicable MEL for such cases...
xxx
Fuel jettison areas are sometimes designated, for environmental reasons, i.e. over water, or sparsely populated areas, but in an emergency, the captain can start fuel dump immediately after takeoff, as may be required. Fuel dump nozzles are generally located near the tip of the wings, so, no concerm for aft mounted engines (i.e. 727)...
xxx
Fuel tanks cannot be emptied completely by fuel jettison - there will always be a certain amount of fuel remaining in the "main tanks" after the fuel level reaches a certain low level, the "undumpable fuel" - generally sufficient fuel for some 45 minutes of flying in the landing configuration at low altitude...
xxx
And yes, fuel evaporates before reaching the ground, consider that if we dump in some tropical areas, we indeed take go care of the mosquito problem in that area, but it ruins the taste of tomorrows' seafood dish you will eat...
xxx
 Wink/being sarcastic
(s) Skipper
 
Airbus Lover
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 3:07 pm

Covert, can you tell me more abt the fuel dumping which had led to the demise of SR111, according to your above post?
 
covert
Posts: 1500
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RE: Explain Dumping Fuel?

Sat Oct 12, 2002 3:15 pm

Airbus Lover, I did not say that was the reason for the demise I was merely speculating that if the pilot had decided to make an overweight landing in Halifax, the warping of insulation wires causing the fire that was determined to be the cause of the accident would not have had a chance to happen...Even if it did happen, 111 would be on the ground, empty of pax and crew...

Sincerely,
covert
none
 
airplay
Posts: 3369
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 7:05 am

Fuel tanks cannot be emptied completely by fuel jettison - there will always be a certain amount of fuel remaining in the "main tanks" after the fuel level reaches a certain low level, the "undumpable fuel" - generally sufficient fuel for some 45 minutes of flying in the landing configuration at low altitude...

This is not always the case. There was a New Gomair 707 that dumped all of it's fuel then crashed after the engines quit. I believe C-130s suffer the same deficiency. You can check out the details on the 707 here:

http://www.airdisaster.com/photos/9xr-is/photo.shtml

is this quite damaging to the environment?

Of course it is. You won't find anyone associated with aviation in a hurry to open that can of worms. Besides serious effects on the respiratory system, Jet fuel contains several known carcingens. Is it any wonder that so many frogs are born deformed and the amount of children born with asthma is increasing?

 
OPNLguy
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 7:33 am

>>>This is not always the case. There was a New Gomair 707 that dumped all of it's fuel then crashed after the engines quit.

I spoke with a buddy of mine who has 707/KC-135 experience, and he confirmed my recollection that you can only dump down to a certain amount and not run the tanks dry.

In reading the brief accident info at the link you included, it's quite possible (the Congolese engineer's comments notwithstanding) that the crew underestimated the amount of fuel required for the diversion due to increased fuel consumption from the extended gear, and dumped an amount to consider a "normal" configuration, thus running short at the last minute. It's anazing how fast some non-standard configurations can burn fuel, with the Hapag-Lloyd A310 at VIE as just one example...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Guest

RE: Explain Dumping Fuel?

Sun Oct 13, 2002 8:11 am

Dear Airplay -
Are you a pilot, or a maintenance technician with 707 systems knowledge...?
xxx
The 707, 720, 727, 747 and DC8 are FAR/JAR 25 aircraft equipped with jettison system, and a provision for preserving a certain amount of fuel in the main tanks which do feed engines directly - a "fool proof system"... it was designed with that purpose in mind... I only know these types of airplanes, as I am (or was) qualified in them...
xxx
Further, when I make statements here in the forum, I try to provide the most accurate answers possible to a lot of people who wish acquire knowledge for various reasons. I avoid providing answers which risk to mis-educate people.
xxx
That 707 you mention (I read the article with the link) obviously ran out of fuel, but it would have been impossible to drain the main tanks completely by the jettison system. Some 6 to 7,000 kgs total of fuel would have remained below the standpipe level of main tanks nbr 1, 2, 3, and 4... The center wing tank, and the reserve tanks 1 and 4 would have been empty, yes...
xxx
It is therefore obvious that the aircraft ran out of fuel, after dumping all the fuel they could jettison, then, with gear down, the engines eventually ran the tanks dry and empty. They ran out of fuel having dumped more than they should have dumped, and probably continued to fly some 45 minutes thereafter... The text does not explain THAT FACT... but you use your limited understanding of the 707 fuel system, to basically tell me - Skipper, you dont know your "stuff", and you provide your own expert explanation...
xxx
I could probably have suggested deletion of you statement, however I wish to educate you and others as to the danger of misunderstanding of news media press releases...
xxx
You "believe" the C-130 suffers the same deficiency...? Is that a firm word you give us... I do not know the C-130, which is not certificated by FAR/JAR 25... but the L-382 is, and as is, it must have that provision as well. Personally, when I am not sure about something, I seek notoriety with my silence...
xxx
I say again, a 707 cannot dump fuel to dry the main tanks. Period...

(s) Skipper
 
trickijedi
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 8:31 am

Yup! I wouldn't argue with the Skipper. Period.
Its better to be on the ground wishing you were in the air than be in the air wishing you were on the ground. Fly safe!
 
EssentialPowr
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 1:15 pm

The classic statement, which only illustrates basic ignorance of chemistry...

"Evaporation" is simply a change in phase - not a hocus pocus, rabbit in the hat dissappearance. If the fuel evaporates, like many other substances in the the atmosphere (water vapor (rain!!!)....) Where does it go?


Well...where does the rain go?

Are we paying teachers in the US secondary education system to "teach" this? And people accept it? Or is this one of the most ignorant of "urban myths?"
 
EssentialPowr
Posts: 1646
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 1:24 pm

BTW - the last TV news report of an a/c that returned to IAH after dumping fuel indicated that the fuel dumped by the a/c was not an environmental hazzard, b/c it "would evaporate" and thus be eliminated from our ecosystem as we know it by that simple process...


People, pls read your 3rd grade science book when you pass through...
 
airplay
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 1:34 pm

Gee Skipper,

I guess since you spared my post I won't suggest the deletion of yours either even though it contains inaccuracies.

First of all, all the aircraft you mentioned except for the 747 are NOT FAR/JAR 25. The certification basis for the Boeings and the DC-8 is CAR 4b. The certification basis for the L382 (except the J) is CAR 1/CAR 9a/CAR4b.

In the matter of fuel jettisoning, CAR 4b is very similar to FAR 25 in that both essentially state:

The design of the jettisoning system shall be such that it would not be possible to jettison fuel in the tanks used for take-off and landing below the level providing 45 minutes at 75% maximum continuous power except that it shall be permissible to jettison all fuel where an auxiliary control is provided independent of the main jettisoning control.

I do not profess to be an expert on the 707 (Thank God) so I don’t know if it has an auxiliary control that allows the pilot to empty the tanks but the accident report I posted seems to suggest it is possible and if it does it is well in compliance with the original design standard. If I’m wrong, fine. That’s the whole purpose of these forums, to discuss issues. Not to be scared to speak up in fear that the all-knowing “Skipper” will suggest deletion.

I do not know the C-130, which is not certificated by FAR/JAR 25... but the L-382 is, and as is, it must have that provision as well. Personally, when I am not sure about something, I seek notoriety with my silence...

You made a inaccurate statement about an airplane you don’t profess to be an expert on then claim that you don’t do that sort of thing. Looks like you’re guilty of exactly what you accuse me of....all in a single sentence.

Yup! I wouldn't argue with the Skipper. Period.

TrikiJedi,

I don’t let Skipper intimidate me, I suggest you don’t either. If you have an issue or find room for improvement in a post, share it.



 
Guest

RE: Explain Dumping Fuel?

Sun Oct 13, 2002 4:49 pm

Correct Airplay -
xxx
Both 707 and DC8 were CAR 4b, since transport category aircraft were subject to CAR 4b in 1958/59...
727 is a straight FAR 25 aircraft as applicable in 1963...
747 was originally certificated straight FAR 25 in 1969... It is only later time that JAR/FAR were amended to meet essentially the same requirements...
xxx
I made an (obvious) error in citing JAR/FAR 25 as the certification standards of the listed aircraft, because it is "the way I name", erroneously, all transport category aircraft in my classrooms or lectures in aviation academies, as few crewmembers are interessed in the historical aspects of the aircraft certification...
xxx
I maintain what I said about "undumpable fuel" - you are likely to see a series of threads which will verify that fuel jettison systems do not dump fuel below a certain amount of fuel... the tragedy on that 707 as I read it was blatant lack of fuel management and planning... Gear that will not "retract" does not constitute a need to dump fuel as if it was an emergency, it is merely a malfunction. I doubt that the crew had any justification to dump fuel if it was merely a gear retraction problem. Gear extension problem is another story. The runway at Bangui airport is 8,530 feet long, adequate for a 707 landing.
xxx
I take good note of your C-130 (L-382) expertise, I never flew such type of aircraft, and like you, failing to limit your discourse within the limits of your knowledge, I should have not mentioned the C-130 civilian equivalent, since instead, you are educating me of the L-382... I shall refrain from comparing airplanes on which I do not hold a type rating... I clearly stated that I was not knowledgeable about the C-130 - but you made it clear you were...
xxx
My apologies -
(s) Skipper

P.S. To justify my dislike of erroneous statements (i.e. the 707 accident) it is that often, some enthusiasts acquire knowledge of correct (and unfortunately incorrect) statements made in this A.net Forum...
Then, imagine that such enthusiast may be a TV anchorman who will "quote educated sources" that such airplane accident was due to... "x" technical reason, and his public will be misinformed... snowball effect with the public already so biased in their ideas about the aviation industry.
Another danger here is that some young pilots learning to fly may inspire theiselves of "legends" that they have read from (us) experts - or so called experts... the least of which problem would be for them to fail an oral exam for licensing, but to another extreme, could lead them to an accident...
 
dragogoalie
Posts: 1172
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 8:21 pm

"The classic statement, which only illustrates basic ignorance of chemistry...

"Evaporation" is simply a change in phase - not a hocus pocus, rabbit in the hat dissappearance. If the fuel evaporates, like many other substances in the the atmosphere (water vapor (rain!!!)....) Where does it go?


Well...where does the rain go?

Are we paying teachers in the US secondary education system to "teach" this? And people accept it? Or is this one of the most ignorant of "urban myths?""

That is true, however the fuel will also sink into the environment if the plane lands overweight, runs off the end of the runway crashing into whatever is there possibly killing hundreds of people. Take your pick  Wink/being sarcastic

--dragogoalie-#88--
Formerly known as Jap. Srsly. AUSTRALIA: 2 days!
 
covert
Posts: 1500
Joined: Sun Oct 21, 2001 1:02 am

RE: Explain Dumping Fuel?

Sun Oct 13, 2002 8:42 pm

Hello people,
This really isn't the place to rally support for environmentalist drives...I think 90% of us here on airliners.net love airplanes, and if you start to question the main thing that make them go 'round, jet fuel, most probably nobody wants to hear that "oh, jet fuel and avgas pollute the environment, so we really shouldn't fly." That sounds pretty ludicrous to me. Besides jets only account for two percent of emissions....

And Airplay is challenging B747Skipper's position, I think he just made a generalization, take it easy. I feverently believe he is 100% competent and knows what he is talking about. We all tend to dumb things down a little bit in day to day life, but not apparently one person may take it a different way...

Sincerely,
covert

just as long as it doesn't mess my clothes up...
none
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Explain Dumping Fuel?

Sun Oct 13, 2002 11:27 pm

Who stated we shouldn't fly??? Don't recall reading that.

I'm just pleading for people to learn what "evaporation" means; that word comes up EVERY time a fuel dump question arises, and someone always offers the same poor explanation.
 
covert
Posts: 1500
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RE: Explain Dumping Fuel?

Sun Oct 13, 2002 11:43 pm

If you are saying tha noone on this forum remembers basic physics, at least I do. I still remember all about how solids/liquids/gases interact. I know that evaporation is the conversion of a liquid into a gaseous state(vapour) at a temperature below the boiling point. I still know the difference between evaporation, sublimation and condensation....

Just because we are wannabes in aviation doesn't mean we don't excel at what we are doing now...

Sincerely,
covert
none
 
luzezito
Posts: 250
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RE: Explain Dumping Fuel?

Mon Oct 14, 2002 12:04 am

I have a further question on this matter: do you remember the Air Transat Airbus that glided and successfully landed in the Azores? It has been discussed already but I do not find it in my search. Was it not because crew inadvertedly dumped fuel?
Please don't crucify me if I am wrong. I do not engage in the aforeposted ego war  Wink/being sarcastic
Quoniam Vita Brevis Est, Propera!
 
Staffan
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RE: Explain Dumping Fuel?

Mon Oct 14, 2002 12:31 am

Luzezito, I recall something about a leak in one wing and to compensate the lower level of fuel in the leaking wing they started cross-feeding fuel from the other one, and in that way they managed to dump all their fuel.

Staffan
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 2:08 am

727 is a straight FAR 25 aircraft as applicable in 1963...

That is incorrect. The 727 is CAR 4b:

http://www1.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/CurrentModelsbyTCHolder/7BDC1D15D8005E8085256722006B0D0C?OpenDocument

The initial issue of FAR 25 was in 1965 so it did not exist in 1963. You can check it out here:

http://www1.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/MainFrame?OpenFrameSet

This is not a challenge, just a clarification. CAR 4b is much less stringent than FAR 25, especially at the current amendment.

Although I am not familiar with every fuel jettison system, many utilize existing pumps for the dual purpose of backup and jettison. Skipper, doesn’t the 747 also do this? Aren’t the override/jettison pumps capable of accessing virtually all of the fuel? Otherwise, in the override role they wouldn’t be able to utilize all usable fuel. If I’m not mistaken, the only thing stopping all the fuel from being jettisoned is the jettison nozzle valve which under normal conditions will shut before reaching the “Fuel to Remain” level, but pressurized fuel will still be available behind the valve. There is no physical offset “stand pipe” that I can find. Can these jettison nozzles be overridden?

The DC-10/MD-11/KC-10 use an electronic controller rather than a physical stand-pipe to automatically cease fuel dumping before the "Fuel to Remain" limit. As the following AD illustrates, a bus fault that was not previously considered can cause all of the fuel to be jettisoned:

http://www2.airweb.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/26832E4EC33BB54E86256A0800650079?OpenDocument&Highlight=fuel%20dump

Of course this unfortunate event is caused by a fault, and not under normal operating conditions, but it serves to illustrate that sometimes systems are not as fool proof as we sometimes think, and that at least in these aircraft the pumps used to jettison have access to all usable fuel.
 
Guest

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 3:23 am

Airplay -
My old PanAm, 727-21 flight manual says in print...
"Certification status" - Transport Category FAR 25 (CAR 4b)

That page was printed by PanAm in 1968...
(s) Skipper
 
Guest

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 3:41 am

Airplay -
In the 747 fuel is dumped trough 6 override-jettison pumps (2 in center wing tank, 2 in each inboard main tank) and the system is also used to transfer fuel from tank to tank... transfer fuel tank to tank was impossible in the 707 and the 727... so we often use the same fuel line to transfer fuel... If a jettison nozzle valve would fail open it would "dry" the center wing tank, the reserve tanks 1, 2, 3 and 4, and the main tanks 1 and 4... 12 tons would remain total in the main tanks 2 and 3... to feed the 4 engines... the 12 tons is the 45 minutes fuel - etc - required by FAR 25...
xxx
(s) Skipper
 
Rick767
Posts: 2613
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RE: Explain Dumping Fuel?

Mon Oct 14, 2002 4:07 am

Just to add some technical data from the 767-300(ER) we operate. Remember that a fuel jettison system remains a company option on these aircraft. They are certified to land up to MTOW in an emergency. Just last year one of our aircraft did return to EGCC on a flight to Florida, almost 40 tonnes "overweight", after smoke in the cabin after takeoff. Clearly this is one case in which the crew correctly decided to land overweight, and it resulted in no damage to the aircraft.

Jettison is provided for the CENTRE tank only, the two nozzles jettison fuel at around 1,200 kg/min maximum meaning 30 minutes to fully empty that tank.

No jettison is provided for the LEFT or RIGHT fuel tanks, at full quantity this means an aircraft GW of 160,000 kgs, which is still 15,000 kgs above MLW anyway!

Personally I think the whole fuel jettison idea is over-rated. Apart from the (discussed) environmental implications, it costs the company a lot of money to simply get rid of all that fuel, and if the runway length and conditions permit I really don't see the point.

Our ops manual is quite clear on this, if any additional hazard (perceived or real) would be presented by taking the time to get rid of the fuel, land overweight.
I used to love the smell of Jet-A in the morning...
 
Guest

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 4:48 am

Airplay -
xxx
The possible failures and contingencies on various airplanes are numerous... Operating a given type of aircraft requires some amount of "systems knowledge" - which all training courses provide... But as to operate with operational insight - there only years of experience and... airmanship can provide "the big picture"...
xxx
We had a slight incident - 2 years ago - where a 747-200 cargo coming from Spain was to land and refuel in Recife, Brazil... the single runway was closed due to a disabled aircraft which was supposed to have been removed within 30 minutes (said the tower)... The captain and flight engineer, both experienced on 747 - elected to keep the reserve tanks 1 and 4 full, to provide for an "aft CG" which reduces drag... The runway did not get cleared on time, the captain elected to proceed to Fortaleza... low fuel situation... then came the time to transfer fuel from reserve tanks to main tanks... one valve failed, trapping 2 tons of fuel in the reserve tanks... they made it to the alternate airport with some 10 minutes fuel left usable...
xxx
In a 747 - you dont keep fuel you depend on to make your landing, in the reserve tanks... I am the flight manager 747... dont you think I had words with that captain and flight engineer...? - If you want Airplay, there is always a potential for a failure... my bag is full of horror stories where a combination of a stupid circuit breaker failure, poor airmanship and lack of planning can lead you to a disaster... Every accident is a combination of at least 2 faults, one of which can be mechanical at the onset, but the problem gets amplified to... disaster by poor airmanship or planning...
xxx
It takes us 4 to 6 weeks to train a 737 pilot to fly a 747... it takes years of experience on the line to acquire airmanship. I often instruct in classrooms and in simulators, or do line training... in simulators, I guarantee you that you can combine "malfunctions" to demonstrate what leads to an unavoidable disaster, no matter what the experience is... I often "replay" previous accident circumstances in simulators to demonstrate that fact...
xxx
The 707 disaster in Bangui was - unfortunately - pilot's fault... it was not their ability to fly the aircraft, it was lack of airmanship and flight planning... and in many other cases, disasters are avoided by knowledgeable crews thanks to their years of experience...
xxx
(s) Skipper  Smile
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 5:01 am

Well said Skipper. Of course I certainly would not suggest that experience isn't foremost in keeping airplanes safe. What I'm trying to establish is whether it is possible or not to dump all the fuel in an airplane - even without a system failure.

Just one more question, isn't it possible in a 747 to transfer fuel from main tanks 1 and 4 to 2 and 3 respectively? In this scenario, if proper fuel management was not exercised (leaving 1 and 4 as reserve) could you not conceivably dump all the fuel in the airplane during a jettison?


 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Explain Dumping Fuel?

Mon Oct 14, 2002 5:11 am

Hmmmm...I may have that sequence in the last question in reverse...
 
Bellerophon
Posts: 516
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RE: Explain Dumping Fuel?

Mon Oct 14, 2002 5:49 am

B747skipper

I agree with most of what you've written, but I think you have slipped up with a small part of your last post where you say:

...If a jettison nozzle valve would fail open it would "dry" the center wing tank, the reserve tanks 1, 2, 3 and 4, and the main tanks 1 and 4... 12 tons would remain total in the main tanks 2 and 3...

In fact the 12 tons or so of fuel that would remain in this situation will be equally distributed amongst all four main tanks.

Tanks 2 & 3, the ones the fuel is actually being jettisoned from, have, as you said previously, a standpipe that will not allow fuel to be jettisoned when the level in the tank gets down to about 3 tons.

Tanks 1 & 4, as I am sure you are aware, do not jettison fuel directly, but instead drain their fuel into tanks 2 & 3, via jettison transfer valves, from where it is jettisoned by the override/jettison pumps in those tanks.

However, most importantly, these jettison transfer valves are set high enough up the dividing wall between the two tanks concerned so that they act in exactly the same manner as a standpipe, and will not allow all the fuel in an outboard main tank to drain into the adjacent inboard main tank, and fuel will cease to drain inboard at around the 3 tons level remaining.

You can drain the Reserve tanks and the Centre Wing Tank, but you can't jettison below around 3 tons in any of the four main tanks, leaving the 12 tons you mentioned, equally distributed.

This principle incidentally applies to all versions of the B747, including the B747-400, where you will have to set it up, not your F/E.

The Boeing B747 fuel system will not allow you to jettison all the fuel on the aircraft by mistake. It cannot however stop someone jettisoning more fuel than was wise, or than they intended, provided they stay above 12 tons standpipe level.

It is up to the pilot to ensure that the amount of fuel left in the aircraft tanks at the end of the jettison is sufficient to get the aircraft to a suitable airfield and land with prudent reserves remaining for unexpected contingencies.


Airplay

You should easily be able to see the standpipes in the fuel schematic for main tanks 2 & 3 in any B747. For main tanks 1 & 4, see my remarks above, although I grant you that these jettison transfer valves are often (incorrectly) called standpipes.

You are correct about the potential fallibility in the electrical protection system on the DC-10 fuel jettison system.

In fact the wrong circuit breaker popping unobserved during fuel jettison could also render the jettison low fuel level protection inoperative. It was a widely known trap, and occurred with monotonous regularity on any simulator check that involved fuel jettisoning.

On a general note, if involved in fuel jettisoning, it is good airmanship to ensure that everyone on the flight deck has "Checked the Maths" and agreed on the amount to be jettisoned, the estimated time that the jettison will take, the amount of fuel that must be left on board, and the quantities and tanks that it should be in at the end of the jettison.

Finally, there are sometimes Centre of Gravity implications to consider when jettisoning large amounts of fuel. On my current type this is the critical factor to consider, before deciding how much we can jettison, but it is also of some importance in other types

In an incident at SFO in the early 1970s, a B747-100, belonging to a well respected US airline, hit some runway approach lighting stanchions on take-off.

The crew did a great job to get the severely damaged aircraft safely back on the ground at SFO, but for various reasons the CoG was just a little too far aft when the aircraft landed, and, after coming to a halt, sad to say, it slowly sat on its tail.

Regards

Bellerophon
 
Guest

RE: Explain Dumping Fuel?

Tue Oct 15, 2002 12:04 pm

Bellerophon -
Overenthusiasm of my fingers (and old age dylexia) - correct - undumpable fuel would remain in mains # 1-2-3-4 - total remaining 12-13 metric tons, or some 28,000 lbs...
xxx
About the 747-100 at SFO - being a traildragger  Wink/being sarcastic
That happened to PanAm, who "forgot" part of their gear during takeoff - the body gear, I think one got missing, the other damaged... Upon dumping and landing (on the wing gear only) the airplane fell on its tail, like you said... not because of dumping but because of missing body gear...
xxx
Actually, the dumping pretty much keeps the CG within limits, Boeing does not mention any "warning" in the fuel dump check lists, nor was it any problem with the 707 and the 727... Maybe some aircraft do have that concern...
xxx
TO DUMP OR NOT TO DUMP - that is the question (Orville Shakespeare)...
Company policy and philosophy is this - if it is an emergency, GO AHEAD, jettison fuel AT ONCE, and dont waste precious minutes to phone patch the company and get an assistant director of operations (half-awake) to clear you to dump the liquid gold... however, if only a malfunction requires landing overweight - go for overweight landing, nothing bad, I have done one at a weight fairly close to maximum takeoff weight...
xxx
Our landing performance tables are not limited to maximum landing weight, either for runway limit - or approach climb - they show the numbers all the way up to the maximum takeoff weights - and if the runway is too short to accommodate such a heavy weight, then, yes, dumping fuel would be required. I even venture to say that if the approach and landing is done with "all engines" operating, dont be concerned about the approach climb limit... the runway limit is the only hard limitation... this, of course, dictated by appropriate review of all factors - you and I call it airmanship again...
xxx
Esso, Shell, BP, Mobil or YPF and the rest of the mafia are not happy with policies that recommend to avoid dumping fuel - screw them...
xxx
(s) Skipper

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