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swarf in fuel tanks blocked the fuel filters

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swarf in fuel tanks blocked the fuel filters

Old 4th Feb 2008, 02:15
  #41 (permalink)  
 
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nojh,

wasn't criticising your use of the word SWARF. Only other posters use of the term FOD, which is a loction for the source of swarf, suggesting the swarf came from outside the a/c. Sorry if it gave the wrong impression.

Brgd's

N1 Vibes
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Old 19th Feb 2009, 16:33
  #42 (permalink)  
 
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how successful have you been? I hope you see my thread created under fuel tanks.
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Old 19th Feb 2009, 17:42
  #43 (permalink)  
 
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On the CFM 56 you can find MCDs and CDs which have a job of indicating an engine part that is failing, on the oil system of the engine.
I dont know the 757 at all but do they use MCDs in fuel or not?
I personally have never seen them on fuel lines.
Oh sorry CD stands for Chip Detector and MCD for Master Chip Detector.
My question is that if it was SWARF it must have been a booster pump structure failure because in my opinion if it was failing slowly slowly you would have had a decrease in pressure of the fuel.
On the other hand if it failed at once you would get booster pump low pressure in my opinion.
Did you have any of the above indications or it just failed out of the blue?
I dont believe it was fuel tank SWARF due to the fact that fuel tanks are integrally sealed with sealants to avoid any leaks and to stop any SWARF been dragged down the pipes.
But on the other hand we have seen cases of aircraft parts and systems failing whne they should not.
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Old 19th Feb 2009, 17:50
  #44 (permalink)  
 
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FOD=foreign object damage or foreign object debri must not be confused with Bird Strike or by damage caused by aircraft parts to the aircraft (SWARF for example).
Is not considered FOD as it is not foreign to the ac.
I believe some n the indstry cal it LOD (local object debri) but I have seen it under other names also.
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Old 19th Feb 2009, 21:19
  #45 (permalink)  
RMC
 
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Swarf contamination of engine fuel feed lines happened on Airbus A300s 25 years ago. It was picked up in the flight testing stage though. There are a few bits of information missing. I fly the 737 and am assuming that (like Airbus) the design philosophy of Boing fuel systems is essentially the same across the product range.

(1) Did the associated fuel pump low pressure light come on (indicative fuel low pressure filter blockage)?
(2) Did the filter bypass light come on (indicative of high pressure filter bypass).

If the engineers are clear that the contamination came from swarf in the tanks then this rules out fuel pump break up.

In UK engineering speak Swarf normally refers to corkscrew shaped strands of metal (or broken pieces of the same strands...large chips which are measured in milimeters). Swarf comes from drilling operations during manufacture or repair.

If your HP filter was blocked by much smaller chips (dust measured in microns rather than millimeters) this would come from reaming operations of high tolerance assemblys such as the wing/tank undercarridge support structure...or from pump break up. It Should not be referred to as swarf.

The fuel filters on all bowsers are huge (and very expensive). The only way swarf could be introduced from a bowser was if the filters had been removed and not replaced during maintenance. Possible but very very unlikely.

Just to clear up the intended function of aircraft sealant ...it is to seal not as someone said to stop swarf being dragged into the pipes.

That said during manufacture swarf can stick to wet sealant ...much later this swarf can be dislodged and settle at the lowest point in the tank.

Without exteremely dilligent inspection swarf will end up making its way down to the fuel pumps during the early weeks and months of an aircrafts life (or following a major repair).

The only thing I find odd is that your engine failed at low power. Both fuel filters have a bypass (although this is achieved in different ways). The only time you should get fuel cavitaiton is at high altitudes..with high power settings?
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Old 19th Feb 2009, 23:06
  #46 (permalink)  
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ASFKAP - Agreed this would not have happened if everything had been done by the book (either during manufacture or repair).In the Airbus case inspection of tanks was not done properly.
I am assuming that the description of swarf from the wing tanks is correct. Unless there has been widespread driling out of bolts (unlikely on a relatively new aircraft) the swarf will be aluminium and won't be picked up by the magnetic chip detector.
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Old 19th Feb 2009, 23:10
  #47 (permalink)  
 
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I said the main purpose is to seal but also to stop swarf due to the fact that the inside of the tanks are not fine surface but have a few rough ends.
I personally disagree that sealant would not stop SWARF as sealant can be up to 10 mm thick.
I am sure some gets away but ae are talking about amounts that could block fuel here so I am sure hat the SWARF did not come form the tanks walls.

At least this is what i was taught at uni doing my B1 lisence.....but i see we agree on the low pressure indication....
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Old 20th Feb 2009, 07:23
  #48 (permalink)  
 
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Avman ,swarf are aluminium particles drill bit residues,etc which acumulates during the construction in the fuel tanks and is supposed to be removed before the delivery of your new multi million pound aeroplane In this case the aircraft flew for 6 months extensively over water before all the filters blocked up. This aircraft was UK Caa registered,makes you wonder does it not ?
Swarf is metal shavings,aluminium or otherwise.
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Old 20th Feb 2009, 09:38
  #49 (permalink)  
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The reason there could have been enough swarf from the wing tanks is that I understood this to be a relatively new aircraft. To give you an idea of the amount of swarf generated during manufacture there are just over 1,000,000 holes to be drilled and filled in each A300 wing.(I spent 16 years working as an engineer at the Airbus wing manufacturing site in Chester). If you think the guy who put that stat together had a sad job have some sympathy for the Boeing guy who calculated that a 747 has a total 45 million parts.

Having applied gallons of sealant inside Airbus wing tanks of during my apprenticeship I can assure you that cured sealant (if applied correctly) will not trap swarf. It has to be applied in a way which ensures there is a free flow of fuel to the pump box area. If fuel (and therefore swarf) starts collecting in pockets (and the unusable fuel level goes up) then the aircraft will fail its critical tank capacity check.

Fark'n'ell - Swarf is generated by drilling holes...the only material in a 757 primary wing box (tank) structure is aluminium so the only drill swarf that can be in a wing tank is aluminium (unless, as I said, someone has been drilling out lots of high tentile steel bolts during a massive repair.

The notes of caution here are:-
1. We had a prolonged strike during my time at Airbus (got a 35 hour week out of that one) and the management and some non unionised workers kept some production going. There are a number of problems with this...in relation to this thread you have people working areas they are not familiar with. If you dont follow the designers instructions on sculpting sealant and ensuring rib drain holes are clear of sealant etc then you could end up with pocket situation mentioned by CY333. Also management in particular were reluctant to go into tanks and do the dirty work necessary to properly remove the mass of swarf. It is not just from cured sealant but the coolant used for drilling the bigger holes keeps smaller swarf particles stuck to the inside surface.
2. Whilst not wanting to start yet another Boeing / Airbus debate there is no question that this would be more likely to happen on a new Boeing than an Airbus. My engineering apprenticeship was five years (too long to be fair)...the majority of Boeing hole drillers and fillers have around that many months. Airbus product build quality is far superior to Boeing. Again the CY333 situation is more likely to occur with what is effectively a semi skilled workforce. This is particularly true when build rates start to increase and you have to take a semi skilled guy off a job he has done all his life ...and put him in a new area which requires tacit knowledge obtained during years of training. As I said in my first post I am now a Boeing driver so this is not an anti American/Boeing post...just the facts.
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Old 20th Feb 2009, 18:57
  #50 (permalink)  
 
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Following fuel problems we removed a wing from a Harrier in Germany many moons ago...only to find the main fuel line full of kimwipe.

Nothing new under the sun....
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Old 22nd Feb 2009, 11:34
  #51 (permalink)  
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We used to use kimwipe (industrial kitchen roll) ....to get swarf out of tanks without leaving fibre traces left by rags! Works better if the kimwipe is taken out afterwards though :-)
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Old 22nd Feb 2009, 18:49
  #52 (permalink)  
 
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Sheeties NEVER, NEVER clean up after themselves, industry standard.
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Old 23rd Feb 2009, 18:56
  #53 (permalink)  
 
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Was once the safety man for a chap working in the fuel tanks of an aircraft in our hangar... he counted everything out (bolts, screws, washers etc.) out before he went into the tank, then counted it all again when he came out.

Said he had found some strange things in these tanks over the years, including, once, a plastic coffee cup... (Though not at the same company, I hasten to add)

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Old 24th Feb 2009, 21:51
  #54 (permalink)  
 
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The B757 does not have MCDs in the Fuel system.

Are there details on Date/time/Registration of the Aircraft available.

regds
MEL
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