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.