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Do All Airliners Have Live Wires In The Fuel Tanks  
User currently offlinePs76 From , joined Dec 1969, posts, RR:
Posted (5 years 2 months 2 weeks 6 days 20 hours ago) and read 4251 times:

Hi,

Just had a quick question as I'm a nervous flier and one of the things I worry about is a situation similar to TWA800 happening. Was just wondering if all airliners have electrical wiring in their fuel tanks or what is there to prevent an incident to TWA800 happening again. I know that jet fuel won't ignite easily but anything else to help put my mind at rest would be cool.

Any info welcome.

Many thanks,

Pierre.

10 replies: All unread, jump to last
 
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 1, posted (5 years 2 months 2 weeks 6 days 19 hours ago) and read 4241 times:



Quoting Ps76 (Thread starter):
Was just wondering if all airliners have electrical wiring in their fuel tanks

Yes.

The fuel quantity probes have electrical wires.

The fuel boost pumps (which are electric motors) have wires.

The fuel fill switch's have electrical wires.

The secret is to keep the wires submersed in fuel so they can't spark.

The reason TWA 800's tank exploded was that there was no fuel in the tank, only fumes.


User currently offlineOkie From United States of America, joined Jul 2003, 2999 posts, RR: 3
Reply 2, posted (5 years 2 months 2 weeks 6 days 7 hours ago) and read 4049 times:



Quoting Ps76 (Thread starter):
Was just wondering if all airliners have electrical wiring in their fuel tanks or what is there to prevent an incident to TWA800 happening again

You have fuel pumps and fuel gauges (wiring) in your automobile as well.

The trick here is what is referred to as lower explosive/ignition limits and upper explosive/ingnition limits. If the fuel to oxygen ratio is to low the vapors will not ignite, if the fuel to oxygen ratio is to high the vapors will not ignite.

Speaking generally taking maintenance functions out of the equation then the only time there should be an issue is the first time you fill an empty tank that you pass through the point where a spark can cause a fire or explosion.

The problem with TWA800 is that they let the tank get empty. A few hundred pounds of Jet-A would have saved the day. Newer aircraft today come with an inerting system that displaces the oxygen in the fuel tanks with nitrogen so it can not ignite.

Okie


User currently offlineWoosie From United States of America, joined May 2006, 115 posts, RR: 2
Reply 3, posted (5 years 2 months 2 weeks 6 days 2 hours ago) and read 3942 times:

C urrently, Yes. I believe the 787 does not have electrical wiring inside the fuel tanks; possibly the A380 doesn't either. Fuel quantity gauging systems insert low current, low power into the tank, to measure capacitance across fuel probes. They are then summed and junction probes and this value is read in the cockpit indicators. Some airplane types also run electrical wiring for fuel pumps in the tanks too.

User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 4, posted (5 years 2 months 2 weeks 6 days ago) and read 3911 times:

The Insulation has to ensure no arcing reaches the fuel vapours.
There are constant call out to check the insulation sleeve ends of wiring attachment to components within the fuel tank.
Also a proposal to fill the Fuel tank with an inert gas was considered.

regds
MEL



Think of the brighter side!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17014 posts, RR: 67
Reply 5, posted (5 years 2 months 2 weeks 5 days 20 hours ago) and read 3871 times:



Quoting Ps76 (Thread starter):
I know that jet fuel won't ignite easily but anything else to help put my mind at rest would be cool.

Jet fuel is VERY hard to ignite. Vapors are easier, but still hard. IIRC TWA800 only happened because of some pretty far out circumstances.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinePs76 From , joined Dec 1969, posts, RR:
Reply 6, posted (5 years 2 months 2 weeks 5 days 13 hours ago) and read 3800 times:

Hi,

Just to say many thanks for the replies. Today I had a flight and hardly worried about the fuel tank exsploding at all so maybe there's hope for me still(!)

Many thanks,

Pierre.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (5 years 2 months 2 weeks 3 days 12 hours ago) and read 3616 times:



Quoting Ps76 (Thread starter):
Was just wondering if all airliners have electrical wiring in their fuel tanks

Generally, yes.

Quoting Ps76 (Thread starter):
or what is there to prevent an incident to TWA800 happening again

After TWA800, the FAA issued a special federal aviation regulation (SFAR88) that required all the OEM's to totally redo their fuel system safety analysis. The details would go on for pages but, suffice to say, it resulted in what is probably the biggest upgrade/retrofit program in the history of commercial aviation. Some models had upwards of two dozen modifications to decrease the possibility of a fuel tank ignition.

Quoting 474218 (Reply 1):
The secret is to keep the wires submersed in fuel so they can't spark.

Although that does work, it's not the design criteria. The only acceptable criteria today are:
1) Ensure insufficient energy to generate a spark or
2) Ensure that a spark is contained and cannot ignite the fuel tank ullage

Almost everything in the fuel tank is designed to 1) except the boost pumps. They need so much power than 1) isn't an option, so they use 2).

Quoting Okie (Reply 2):
The problem with TWA800 is that they let the tank get empty. A few hundred pounds of Jet-A would have saved the day.

TWA800 had a few hundred pounds of Jet-A (probably more than that). The dead volume in a fuel tank that size is considerable. The only way to get a tank truly empty is to sump it, then crawl inside with absorbers. Neither one of those things was done prior to TWA800.

Tom.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (5 years 2 months 2 weeks 3 days 11 hours ago) and read 3613 times:



Quoting Tdscanuck (Reply 7):
Although that does work, it's not the design criteria.

Shortly after the TWA800 incident the FAA mandated that all aircraft equipped with fuel tanks in the center wing box be operated minimum amount of fuel in the tank. This was to insure all wiring would be submerged. I am sure that rule has been rescinded but when it was I don't know.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 9, posted (5 years 2 months 2 weeks 2 days 20 hours ago) and read 3531 times:

Yes they do, the scavenge pumps and fuel probes are of the low voltage type...pictured below is a center wing tank fuel probe from a 747/200. The end with the black cap is the end that is submerged in the fuel. Generally speaking, this is the bottom end of the probe, it is rather long (tall).
Big version: Width: 1024 Height: 683 File size: 550kb
747/200 cntrwing tank probe...


User currently offlineBoeing767mech From United States of America, joined Dec 2000, 1025 posts, RR: 3
Reply 10, posted (5 years 2 months 2 weeks 2 days 15 hours ago) and read 3498 times:



Quoting HAWK21M (Reply 4):
Also a proposal to fill the Fuel tank with an inert gas was considered.

It is fitted on our new 737-800's, check out ATA 47 for the new Nitrogen Generating System (NGS)

Quoting 474218 (Reply 8):

Shortly after the TWA800 incident the FAA mandated that all aircraft equipped with fuel tanks in the center wing box be operated minimum amount of fuel in the tank. This was to insure all wiring would be submerged. I am sure that rule has been rescinded but when it was I don't know.

We run our tanks empty.

David



Never under-estimate the predictably of stupidty
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