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neomax
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What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 5:08 pm

To my knowledge, following TWA800, it was mandated to implement a fuel-inerting system on 747's as one of the main results of the investigation. In recent times, it has been known better as being a component so expensive that airlines have opted to retire 747's instead of fitting it. But what exactly is it?

On a side note, if all 747's following TWA800 were required to have this, then how come airlines such as DL and UA were allowed to fly without it and thus retired their fleet once they were required to fit it?
 
VetteDude
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 5:12 pm

I believe, although I'm not certain, that it has to do with replacing the empty tank space (the air in the tank) with nitrogen (which is an inert gas) instead of normal air which has reactive oxygen.
 
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XAM2175
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 5:42 pm

As VetteDude notes, inerting systems prevent the build-up of dangerous fuel-air mixes in partially-full fuel tanks, and most do this by replacing the air in the tank with nitrogen, which is not flammable.

neomax wrote:
if all 747's following TWA800 were required to have this, then how come airlines such as DL and UA were allowed to fly without it and thus retired their fleet once they were required to fit it?


The rule was not implemented immediately - first the NTSB had to complete their investigation of the TW800 incident and definitively find fuel vapour as a probable cause, then the FAA had to take their actions from the NTSB findings and develop a proposed rule, circulate it, etc etc, and then finally issue it - which didn't occur until 21 Jul 2008, and the deadlines for compliance were yet later.

It should also be noted the rules applies to many more aircraft than 747s. For example, an inerting system is required to be installed on all 737s, 747s, 767s, 777s, A320-series, A330s, and A340s produced after 27 Dec 2010, plus all of those models and also 757s, A300s, and A310s (all regardless of age) if they are operated past the relevant airline's full-compliance deadline. On the other hand, full exemptions from compliance apply to aircraft certified for cargo only, aircraft below a certain MTOW, aircraft that use fuel systems that demonstrate an equivalent or greater level of safety by other means (such as the A380), and all L-1011s, DC-9s, DC-10s, and 727s on the basis that the numbers in use and the time they were expected to remain in use made compliance an unreasonable burden on operators.

The deadline for full compliance ended up being 27 Dec 2017* - hence the flurry of retirements leading up to that date.

(* = provisions apply for extension to 27 Dec 2018 based on specific circumstances).

The FAA Advisory Circular is a tough read but does explain the rule comprehensively: https://www.faa.gov/documentLibrary/med ... 20-98A.pdf
 
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SuseJ772
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 8:17 pm

What I have always wondered is where does the Nitrogen come from? Are there tanks? When / how are they refilled? Or is there a extraction device that pulls it from the atmosphere?
Currently at PIE, requesting FWA >> >>
 
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N747PA
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 8:49 pm

Here is a training manual produced for FedEx about the 767 NGS system:

http://www.scribd.com/document/287049556/B767-ATA-47-Student-Book
 
Newbiepilot
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 9:02 pm

SuseJ772 wrote:
What I have always wondered is where does the Nitrogen come from? Are there tanks? When / how are they refilled? Or is there a extraction device that pulls it from the atmosphere?


There is an air separation module with a membrane that pulls oxygen out of normal air. It drops the oxygen content from over 20% to 10-15%, which is low enough to prevent flames from burning
 
CRJ900
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 10:33 pm

Are CRJs, E-jets, A220, Superjet etc exempted as their MTOW is lower than the B737s and A32X?
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Dalmd88
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 22, 2018 10:53 pm

CRJ900 wrote:
Are CRJs, E-jets, A220, Superjet etc exempted as their MTOW is lower than the B737s and A32X?

They are exempt do to their fuel tank configurations. All of the AD effected airframes have the air conditioning packs under the center fuel tank. The heat from the pack area raises the temp of the center tank making an empty or near empty tank more likely to explode if there is a spark. Along with the NGS system there were various wiring mods that had to be done in the tank areas to lessen the chance of a spark. I spent many hours putting Teflon sleeving over wire bundles running outside of the tanks. I also replaced a lot of fuel shutoff valves and boost pumps to comply with the AD's.
 
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OneSexyL1011
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 1:36 am

All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800
 
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MassAppeal
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 2:09 am

XAM2175 wrote:
As VetteDude notes, inerting systems prevent the build-up of dangerous fuel-air mixes in partially-full fuel tanks, and most do this by replacing the air in the tank with nitrogen, which is not flammable.

neomax wrote:
if all 747's following TWA800 were required to have this, then how come airlines such as DL and UA were allowed to fly without it and thus retired their fleet once they were required to fit it?


The rule was not implemented immediately - first the NTSB had to complete their investigation of the TW800 incident and definitively find fuel vapour as a probable cause, then the FAA had to take their actions from the NTSB findings and develop a proposed rule, circulate it, etc etc, and then finally issue it - which didn't occur until 21 Jul 2008, and the deadlines for compliance were yet later.

It should also be noted the rules applies to many more aircraft than 747s. For example, an inerting system is required to be installed on all 737s, 747s, 767s, 777s, A320-series, A330s, and A340s produced after 27 Dec 2010, plus all of those models and also 757s, A300s, and A310s (all regardless of age) if they are operated past the relevant airline's full-compliance deadline. On the other hand, full exemptions from compliance apply to aircraft certified for cargo only, aircraft below a certain MTOW, aircraft that use fuel systems that demonstrate an equivalent or greater level of safety by other means (such as the A380), and all L-1011s, DC-9s, DC-10s, and 727s on the basis that the numbers in use and the time they were expected to remain in use made compliance an unreasonable burden on operators.

The deadline for full compliance ended up being 27 Dec 2017* - hence the flurry of retirements leading up to that date.

(* = provisions apply for extension to 27 Dec 2018 based on specific circumstances).

The FAA Advisory Circular is a tough read but does explain the rule comprehensively: https://www.faa.gov/documentLibrary/med ... 20-98A.pdf


What is it about the A-380, L-1011, etc that they don't need this. This is interesting.

How much does this system weigh? How do we know its working?
 
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N747PA
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 2:19 am

MassAppeal wrote:
What is it about the A-380, L-1011, etc that they don't need this. This is interesting.



L-1011s, DC-10s/MD-11s,Douglas T-tails and A-380s do not have packs directly under the center fuel tank. Some are in the nose (Widebody tri-jets), some in the tail (Douglas T-tails) and in the wing leading edges (A-380).
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 3:42 am

OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

At face value it does seem odd that since the dawn of the Jet Age, that all of a sudden in 1996 planes with A/C packs located under the CWT started exploding in mid air. https://en.wikipedia.org/wiki/TWA_Fligh ... y_theories

"Official" version: https://en.wikipedia.org/wiki/TWA_Flight_800 (Conclusions)
 
JayinKitsap
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 4:43 am

I think I recall that the 787 being a new design is required to have inerting in all tanks or something like that. Grandfathered planes like the 737 have not been required to add outside of the center fuel tank.
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 5:36 am

A very interesting read: https://www.scribd.com/document/2870495 ... udent-Book
According to the linked document, the NGS system works with a maintained air temperature (170F) delivered to the ASM's (Air Separation Modules) that is well above the flash point of Jet A fuel which according to Wikipedia is 100F. There is no additional cooling after the ASM's.

Strange. The system must work as designed. There has only been one NGS equipped plane that's been shot down by a missile (Malaysian Flight 17).
 
WIederling
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 8:48 am

stratclub wrote:
A very interesting read: https://www.scribd.com/document/2870495 ... udent-Book
According to the linked document, the NGS system works with a maintained air temperature (170F) delivered to the ASM's (Air Separation Modules) that is well above the flash point of Jet A fuel which according to Wikipedia is 100F. There is no additional


* Flash point is not autoignition.

* Flash point is determined for 21% O2 at 1000mbar.

* The gas flow into the tank is equivalent to the fuel outflow.

* Adding 100°F slow gas flow to a much larger gas volume will not change the larger volumes temperature in any meaningful way.

* The gas volume above the fuel already is "inerted".
Murphy is an optimist
 
Dalmd88
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 1:20 pm

OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

Every time I worked on one of the AD related cards I would think, "This will prevent it from exploding when the missile hits." I also don't buy the TWA 800 fuel vapor story. Planes were flying around for decades with this pack/tank combo with zero incidents.

For me these AD's were a money maker so I can't complain.
 
kalvado
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 4:44 pm

Dalmd88 wrote:
OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

Every time I worked on one of the AD related cards I would think, "This will prevent it from exploding when the missile hits." I also don't buy the TWA 800 fuel vapor story. Planes were flying around for decades with this pack/tank combo with zero incidents.

For me these AD's were a money maker so I can't complain.

Once upon a time, I happened to talk with a pilot who was on a flight deck of this bird when things went wrong:
Image
While USAF didn't publish a report, the same problem with the tank vapors was one of the suspects. Until you believe that a B-52 was shot down over the runway of a USAF base in continental US..
UPD: actually
when an overheated fuel pump caused an explosion in the aft fuel tank

https://aviation-safety.net/wikibase/wiki.php?id=48281
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 7:47 pm

WIederling wrote:
stratclub wrote:
A very interesting read: https://www.scribd.com/document/2870495 ... udent-Book
According to the linked document, the NGS system works with a maintained air temperature (170F) delivered to the ASM's (Air Separation Modules) that is well above the flash point of Jet A fuel which according to Wikipedia is 100F. There is no additional


* Flash point is not autoignition.

* Flash point is determined for 21% O2 at 1000mbar.

* The gas flow into the tank is equivalent to the fuel outflow.

* Adding 100°F slow gas flow to a much larger gas volume will not change the larger volumes temperature in any meaningful way.

* The gas volume above the fuel already is "inerted".

I could be wrong, but from what I read, autoignition was not considered to be the cause of the explosion. The more likely cause was an empty CWT being heating from the packs and an electrical spark or short.

"Autoignition temperature. The autoignition temperature or kindling point of a substance is the lowest temperature at which it spontaneously ignites in normal atmosphere without an external source of ignition, such as a flame or spark".

I do agree that the 170F air that is inerted and pumped into the CWT, would be of an insignificant amount to raise the temp in the CWT very much if any amount at all. I just thought that how the system works was interesting. With the air in the tank not being able to support combustion (inerted), Flash point and autoignition temp are rendered irrelevant.
Last edited by stratclub on Sun Sep 23, 2018 7:56 pm, edited 2 times in total.
 
Redbellyguppy
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 23, 2018 7:50 pm

It works just like a portable oxygen concentrator, but backwards. Oxygen is the waste product, not the nitrogen.
 
MatthewDB
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Re: What exactly is the fuel-inerting system on 747's?

Mon Sep 24, 2018 6:38 am

There are hardly "no events" of tanks blowing up. There is this one too:

https://en.wikipedia.org/wiki/Philippin ... Flight_143

Jet fuel is quite a bit more dangerous to handle than gasoline or diesel. Gasoline in a closed tank at most outdoor temperatures won't burn because the gasoline fumes displace enough oxygen that it can't explode. Diesel has so little fuel vapor, it won't. A tank partially full of Jet A on a warm day is a bomb save for a lack of an ignition source.

In most aircraft the fuel never gets that warm. Leftover fuel is very cold, and fuel loaded is around ground temperature and it cools shortly after takeoff. If a plane is parked in hot weather, it can be dangerous for a while after takeoff, but that's rare. It is center tanks that aren't being used, just like TWA800, that are particularly dangerous. They can linger for long times in a dangerous state as they aren't chilled fast like a wing tank would be.
 
FlyHossD
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Re: What exactly is the fuel-inerting system on 747's?

Mon Sep 24, 2018 4:53 pm

XAM2175 wrote:
As VetteDude notes, inerting systems prevent the build-up of dangerous fuel-air mixes in partially-full fuel tanks, and most do this by replacing the air in the tank with nitrogen, which is not flammable.

neomax wrote:
if all 747's following TWA800 were required to have this, then how come airlines such as DL and UA were allowed to fly without it and thus retired their fleet once they were required to fit it?


The rule was not implemented immediately - first the NTSB had to complete their investigation of the TW800 incident and definitively find fuel vapour as a probable cause, then the FAA had to take their actions from the NTSB findings and develop a proposed rule, circulate it, etc etc, and then finally issue it - which didn't occur until 21 Jul 2008, and the deadlines for compliance were yet later.

It should also be noted the rules applies to many more aircraft than 747s. For example, an inerting system is required to be installed on all 737s, 747s, 767s, 777s, A320-series, A330s, and A340s produced after 27 Dec 2010, plus all of those models and also 757s, A300s, and A310s (all regardless of age) if they are operated past the relevant airline's full-compliance deadline. On the other hand, full exemptions from compliance apply to aircraft certified for cargo only, aircraft below a certain MTOW, aircraft that use fuel systems that demonstrate an equivalent or greater level of safety by other means (such as the A380), and all L-1011s, DC-9s, DC-10s, and 727s on the basis that the numbers in use and the time they were expected to remain in use made compliance an unreasonable burden on operators.

The deadline for full compliance ended up being 27 Dec 2017* - hence the flurry of retirements leading up to that date.

(* = provisions apply for extension to 27 Dec 2018 based on specific circumstances).

The FAA Advisory Circular is a tough read but does explain the rule comprehensively: https://www.faa.gov/documentLibrary/med ... 20-98A.pdf


Excellent post, thank you.
My statements do not represent my former employer or my current employer and are my opinions only.
 
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trpmb6
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Re: What exactly is the fuel-inerting system on 747's?

Mon Sep 24, 2018 6:03 pm

Interestingly, had the rule that you can't depart with luggage on board when the passenger is not on board not been implemented after the Lockerbie bombing they probably would have been fine.
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Mon Sep 24, 2018 6:33 pm

MatthewDB wrote:
There are hardly "no events" of tanks blowing up. There is this one too:

https://en.wikipedia.org/wiki/Philippin ... Flight_143

Jet fuel is quite a bit more dangerous to handle than gasoline or diesel. Gasoline in a closed tank at most outdoor temperatures won't burn because the gasoline fumes displace enough oxygen that it can't explode. Diesel has so little fuel vapor, it won't. A tank partially full of Jet A on a warm day is a bomb save for a lack of an ignition source.

In most aircraft the fuel never gets that warm. Leftover fuel is very cold, and fuel loaded is around ground temperature and it cools shortly after takeoff. If a plane is parked in hot weather, it can be dangerous for a while after takeoff, but that's rare. It is center tanks that aren't being used, just like TWA800, that are particularly dangerous. They can linger for long times in a dangerous state as they aren't chilled fast like a wing tank would be.

Pardon my attempt at humor. Your post does add some credibility to a CWT explosion on Flight 800. The aircraft may have sat at the gate during the hottest part of the day (July 17, 1996) for several hours after refueling with the APU and packs running. So it would be possible the the CWT fuel was heated above flash point and with having some airspace in the CWT after taxi and take off and possibly an electrical short or spark occurred because of frayed wiring, an explosion could have resulted. N93119 was almost 25 years old at the time of the crash.

If there was a cover up, it would have been one of the best cover ups in history....................
 
Lpbri
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Re: What exactly is the fuel-inerting system on 747's?

Mon Sep 24, 2018 8:15 pm

On the newest designs cabin or cargo air is routed to a compressor, then to a heat exchanger, then to another stage of compression, the to a heat exchanger again, then to a filter, the to an air separation module. Here most oxygen molecules are removed and vented overboard. What is produced is called "Nitrogen Enriched Air", which is then sent to the fuel tanks via piccolo tubes. What happens inside the ASM is a little chemistry. Air flows over separation membranes to separate the oxygen. There is no cockpit control over any of this, except a status message is displayed if there is a fault. There is an MEL for dispatch.
 
T prop
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Re: What exactly is the fuel-inerting system on 747's?

Sat Sep 29, 2018 7:58 am

Dalmd88 wrote:
CRJ900 wrote:
Are CRJs, E-jets, A220, Superjet etc exempted as their MTOW is lower than the B737s and A32X?

They are exempt do to their fuel tank configurations. All of the AD effected airframes have the air conditioning packs under the center fuel tank. The heat from the pack area raises the temp of the center tank making an empty or near empty tank more likely to explode if there is a spark. Along with the NGS system there were various wiring mods that had to be done in the tank areas to lessen the chance of a spark. I spent many hours putting Teflon sleeving over wire bundles running outside of the tanks. I also replaced a lot of fuel shutoff valves and boost pumps to comply with the AD's.


I think the C- Series has a FTIS, I recall seeing placards on the fuel tank access panels that say 'Low oxygen content possible during FTIS operation'.
 
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Balerit
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Re: What exactly is the fuel-inerting system on 747's?

Sun Sep 30, 2018 11:43 pm

stratclub wrote:
MatthewDB wrote:
There are hardly "no events" of tanks blowing up. There is this one too:

https://en.wikipedia.org/wiki/Philippin ... Flight_143

Jet fuel is quite a bit more dangerous to handle than gasoline or diesel. Gasoline in a closed tank at most outdoor temperatures won't burn because the gasoline fumes displace enough oxygen that it can't explode. Diesel has so little fuel vapor, it won't. A tank partially full of Jet A on a warm day is a bomb save for a lack of an ignition source.

In most aircraft the fuel never gets that warm. Leftover fuel is very cold, and fuel loaded is around ground temperature and it cools shortly after takeoff. If a plane is parked in hot weather, it can be dangerous for a while after takeoff, but that's rare. It is center tanks that aren't being used, just like TWA800, that are particularly dangerous. They can linger for long times in a dangerous state as they aren't chilled fast like a wing tank would be.

Pardon my attempt at humor. Your post does add some credibility to a CWT explosion on Flight 800. The aircraft may have sat at the gate during the hottest part of the day (July 17, 1996) for several hours after refueling with the APU and packs running. So it would be possible the the CWT fuel was heated above flash point and with having some airspace in the CWT after taxi and take off and possibly an electrical short or spark occurred because of frayed wiring, an explosion could have resulted. N93119 was almost 25 years old at the time of the crash.

If there was a cover up, it would have been one of the best cover ups in history....................


At SAA in JNB we ran our 747's packs in much higher temperatures for long periods and never ever had problems. TWA 800 and all other 747's that crashed in sum lar circumstances was as a result of section 41 structural failure.
Licensed Aircraft Maintenance Engineer (retired).
 
wpnstroop
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 09, 2018 6:50 am

It doesn’t prevent missile attacks
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 09, 2018 12:54 pm

wpnstroop wrote:
It doesn’t prevent missile attacks

It must be pretty effective because only one plane has been shot down by a missile since NGS systems have become a requirement. Statistics never lie................https://en.wikipedia.org/wiki/List_of_a ... _incidents

For those that like a well executed cover up theory: http://plane-truth.com/fatigue_details.htm
 
spacecadet
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Re: What exactly is the fuel-inerting system on 747's?

Wed Oct 10, 2018 3:21 am

stratclub wrote:
The aircraft may have sat at the gate during the hottest part of the day (July 17, 1996) for several hours after refueling with the APU and packs running. So it would be possible the the CWT fuel was heated above flash point and with having some airspace in the CWT after taxi and take off and possibly an electrical short or spark occurred because of frayed wiring, an explosion could have resulted..


It's not "possible", it was tested and this is what happened. All of this is in the official NTSB report.

A test flight was prepared in identical conditions and on a functionally identical aircraft to TWA 800. The vapor in the fuel tank reached a temperature *well* above that necessary for ignition. The guy who performed the test flight (whose name I can't remember, but he was one of the top investigators at the NTSB at the time and worked on many accidents) was on the episode of Mayday/Air Crash Investigation/Air Disasters about this accident and said he probably wouldn't do that flight again, and he was glad when it was over.

Frayed wiring was found in bundles that run through the center fuel tank, where the insulation was missing. These wires had voltages that *would* have caused an arc. Not could have, but would have. So the NTSB couldn't determine which specific wires arc'd (because that's kind of impossible when so many wires were frayed), but they knew that arcing had occurred, both from looking at the wires and also from dropouts on the flight recorders. (There were also dropouts on flight instruments that the pilots commented on; instruments connected through that same wire bundle.)

What's strange is that this plane hadn't crashed earlier, not that it crashed that day. It just hadn't been in that particular set of conditions before; sitting on the ground for hours after refueling in hot weather with the packs on.

Other 747's very easily could have had similar accidents (and as others have pointed out, various other planes have). But the age of that wiring is a big factor, so not every 747 was equally susceptible. The TWA 800 accident airplane was one of the oldest 747's in the world at that time and that wiring hadn't been looked at in many years.

Again, it's all in the report. But the Air Disasters episode I mentioned is worth watching so you can get a personal perspective and backstory from the investigators to go with the report; and you can also hear from James Kallstrom, who was by his own admission very eager to take over that investigation as a criminal investigation. But even he had to eventually admit that no criminality occurred. It was an accident.
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
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kitplane01
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Re: What exactly is the fuel-inerting system on 747's?

Wed Oct 10, 2018 4:51 pm

XAM2175 wrote:
On the other hand, full exemptions from compliance apply to aircraft certified for cargo only, aircraft below a certain MTOW, aircraft that use fuel systems that demonstrate an equivalent or greater level of safety by other means (such as the A380)



What???? Now I'm curious. What does the A380 do?
 
mikeinatlanta
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 1:56 pm

As others have stated, the NGS is basically a nitrogen generator the pumps high nitrogen gas into the tank to reduce possibility of ignition. Also, the explanation of the timeframe for implementation was a good one.

What is not so good, and frankly shameful, is that the conspiracy theory nonsense would even be allowed on a forum like this one. 230 people lost their lives. Diverting conversations to things like conspiracy theories is counterproductive and undermines all aviation professional's efforts to reduce deaths to zero.

If you are interested in learning more about the causal factors surrounding TWA800, I recommend exploring the EWIS program. While no doubt elevated fuel temperatures contributed to the explosion, many other preventable factors played into it, some of them directly tied to the work of maintenance. The truly remarkable thing is that this hasn't happened more. Imagine if, when the 747 was designed, Boeing engineers had been presented the following information.
1. The 747 will be flying routes with empty center tanks.
2. The airplane will be sitting on the ramp with packs running for hours on end with the center tanks empty.
3. The airline industry will go through a period of deregulation. This deregulation will lead to major efforts to reduce costs by outsourcing maintenance and having certain maintenance (deemed not safety critical) performed by non-licensed technicians. This series of circumstances will lead to the following:
A. During heavy maintenance, and in an effort to reduce costs, floor panels and other open up would be performed by inexperienced personnel. These personnel will be under extreme pressure to the job as quickly as possible, and will essentially do nothing to keep metal shavings and other debris out of wire harnesses while they work.
B. The aircraft's wiring harnesses will essentially have 25 years of being unprotected during maintenance. Not only will they be filled with metal shavings, they will be regularly stepped on, pried out of the way, and otherwise abused, and the abuse will be done by people with little to no knowledge of what that particular wiring does.
C. Close up areas are looked at by inspectors, but not a qualified mechanic. The close up of cabins will be performed by low skill labor, essentially reducing the second set of eyes concept to one set of eyes.

Imagine what Boeing engineers would have done differently had they known the future. Without a doubt they would have been more careful what wiring was grouped in any particular bundle in any airplane. They may have taken measured to keep debris out of wire bundles. I expect they would have taken measures to keep a center tank from becoming super heated as well.

Keep your eye on the ball people. 230 people died and it wasn't a missile, it was us.
Aircraft Maintenance Professional since 1979.
 
SAAFNAV
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 3:53 pm

mikeinatlanta wrote:
Keep your eye on the ball people. 230 people died and it wasn't a missile, it was us.


Excellent response.

I guess that accident was also a missile covered up by the Philippine g'ummint? https://en.wikipedia.org/wiki/Philippin ... Flight_143
L-382 Loadmaster; ex C-130B Navigator
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 6:26 pm

So, exactly what fuel system wiring is routed above the center wing that penetrate into the center wing? The reason for conspiracy theories is that the investigation was not 100% definitive on what the actual cause was. Yes, 230 people lost their lives which is just horrific but censoring people that just want the truth without a shadow of a doubt isn't productive or transparent.

The NGS system is a good think because it does make aircraft safer by design and if we do error, we should always error on the side of safer.
 
mikeinatlanta
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 6:42 pm

There is fuel quantity indication system wiring and pump wiring within the tank. In the fuselage that wiring is bundled with a wide range of other wiring. The only thing not definitive with the investigation is exactly which one of those wires shorted with the other. The reason for conspiracy theories is the twisted satisfaction it provides some people. That's fine for the tin foil hat crowd, but we aviation professionals should take responsibility for our part and never let it happen again. IMO of course.
Aircraft Maintenance Professional since 1979.
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 8:26 pm

Deregulation did not cause the F.A.A to lower maintenance standards. There always has been some carriers and MRO's that have done substandard maintenance although deregulation did cause financial hardships for all carriers and may well have caused some corner cutting by some carriers and the proliferation of MRO's as a way for carriers to cut cost.

https://en.wikipedia.org/wiki/Airline_Deregulation_Act
"The Airline Deregulation Act is a 1978 United States federal law that deregulated the airline industry in the United States, removing U.S. federal government control over such areas as fares, routes and market entry of new airlines, introducing a free market in the commercial airline industry and leading to a great increase in the number of flights, a decrease in fares, and an increase in the number of passengers and miles flown. The Civil Aeronautics Board's powers of regulation were phased out, but the Act did not diminish the regulatory powers of the Federal Aviation Administration (FAA) over all aspects of aviation safety".
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 8:59 pm

mikeinatlanta wrote:
There is fuel quantity indication system wiring and pump wiring within the tank. In the fuselage that wiring is bundled with a wide range of other wiring. The only thing not definitive with the investigation is exactly which one of those wires shorted with the other. The reason for conspiracy theories is the twisted satisfaction it provides some people. That's fine for the tin foil hat crowd, but we aviation professionals should take responsibility for our part and never let it happen again. IMO of course.


I was referring to this statement.
mikeinatlanta wrote:
A. During heavy maintenance, and in an effort to reduce costs, floor panels and other open up would be performed by inexperienced personnel. These personnel will be under extreme pressure to the job as quickly as possible, and will essentially do nothing to keep metal shavings and other debris out of wire harnesses while they work.

From my recollection, CWT wiring does not run underneath floor boards in the cabin. As you noted, there is wiring is inside tank where the possibility of chafed wiring in the FQIS system inside the tank could very well short and ignite fuel vapors. Pump wiring is external and on the rear spar and there is also external wiring on the front spar for electrically actuated valves.
 
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flyingclrs727
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Re: What exactly is the fuel-inerting system on 747's?

Tue Oct 16, 2018 10:28 pm

Dalmd88 wrote:
CRJ900 wrote:
Are CRJs, E-jets, A220, Superjet etc exempted as their MTOW is lower than the B737s and A32X?

They are exempt do to their fuel tank configurations. All of the AD effected airframes have the air conditioning packs under the center fuel tank. The heat from the pack area raises the temp of the center tank making an empty or near empty tank more likely to explode if there is a spark. Along with the NGS system there were various wiring mods that had to be done in the tank areas to lessen the chance of a spark. I spent many hours putting Teflon sleeving over wire bundles running outside of the tanks. I also replaced a lot of fuel shutoff valves and boost pumps to comply with the AD's.


How did anyone ever think that the space underneath a fuel tank would be an appropriate place to put airconditioning equipment? That's got to be as big an engineering oversight as putting 16 psi pure oxygen in the Apollo command module and the Gemini capsules before that.
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Wed Oct 17, 2018 3:59 am

When the 707 was designed, it did not have an APU so running the packs on the ground was for the most part not possible. Over the years future Boeing designs used the same general layout for the ECS system with the packs located underneath the CWT. For ground cooling/heating the preferred method is to use a ground cooling unit, not the aircraft APU and packs.

https://www.youtube.com/watch?v=OEXvIYIhtKM
 
wpnstroop
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Re: What exactly is the fuel-inerting system on 747's?

Tue Feb 05, 2019 7:12 am

stratclub wrote:
wpnstroop wrote:
It doesn’t prevent missile attacks

It must be pretty effective because only one plane has been shot down by a missile since NGS systems have become a requirement. Statistics never lie................https://en.wikipedia.org/wiki/List_of_a ... _incidents

For those that like a well executed cover up theory: http://plane-truth.com/fatigue_details.htm

TWA 800 was not a NGS issue. I, nor any other former TWA employee believe anything other than a missile took that plane down. At my current employer, 737’s fly with the NGS on MEL ALL THE TIME....can’t be THAT important.
 
strfyr51
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Re: What exactly is the fuel-inerting system on 747's?

Tue Feb 05, 2019 8:10 am

OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

, so do I The story was fishy on it's face! It was a cover-up and it was as bogus then? As it is now!
It would be nearly impossible to inert the B747-400's center tank with Nitrogen in a serviceable installation. I can stand up in the damn thing and I'm 5'9".
 
mikeinatlanta
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Re: What exactly is the fuel-inerting system on 747's?

Tue Feb 26, 2019 10:00 pm

wpnstroop wrote:
stratclub wrote:
wpnstroop wrote:
It doesn’t prevent missile attacks

It must be pretty effective because only one plane has been shot down by a missile since NGS systems have become a requirement. Statistics never lie................https://en.wikipedia.org/wiki/List_of_a ... _incidents

For those that like a well executed cover up theory: http://plane-truth.com/fatigue_details.htm

TWA 800 was not a NGS issue. I, nor any other former TWA employee believe anything other than a missile took that plane down. At my current employer, 737’s fly with the NGS on MEL ALL THE TIME....can’t be THAT important.


strfyr51 wrote:
OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

, so do I The story was fishy on it's face! It was a cover-up and it was as bogus then? As it is now!
It would be nearly impossible to inert the B747-400's center tank with Nitrogen in a serviceable installation. I can stand up in the damn thing and I'm 5'9".



What next, flat earthers and chemtrails?
Aircraft Maintenance Professional since 1979.
 
GalaxyFlyer
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Re: What exactly is the fuel-inerting system on 747's?

Tue Feb 26, 2019 10:40 pm

strfyr51 wrote:
OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

, so do I The story was fishy on it's face! It was a cover-up and it was as bogus then? As it is now!
It would be nearly impossible to inert the B747-400's center tank with Nitrogen in a serviceable installation. I can stand up in the damn thing and I'm 5'9".


The C=5 inerted the ullage with motogen and proven to be effective, I’m not sure why you think it doesn’t work. 52,000 gallons of volume, similar size, you walk around in them. You don’t have to eliminate O2, just reduce the oxygen saturation in the ullage to a level that doesn’t support ignition.

GF
 
stratclub
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 2:02 am

I would imagine the NGS system works quit well. If you start with full tanks with very little airspace, as the fuel is burned, the NGS system would just keep up with the expanding air space. Any time the aircraft is powered on, the NGS system is doing it's job.

I can't quit see the correlation though, but anything that helps prevent missile attacks is great in my book. Statistics never lie..............
 
747Whale
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 2:05 am

Dalmd88 wrote:
OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

Every time I worked on one of the AD related cards I would think, "This will prevent it from exploding when the missile hits." I also don't buy the TWA 800 fuel vapor story. Planes were flying around for decades with this pack/tank combo with zero incidents.

For me these AD's were a money maker so I can't complain.


Anyone who knows the fuel system on the 747 Classic knows that the official accounting of TWA 800 is ridiculous and not true. There wasn't a single peer in the Classic whether captain, f/o, FE, mechanic, or loadmaster who remotely entertained the official story as being true; we all knew better.

The CWT did not rupture internally due to arcing or an overheated fuel pump, particularly as the fuel pumps weren't on and the CWT wasn't in use on that flight. Given that wing tanks hold 230,000 lbs, more than needed for the crossing, CWT fuel was unneeded and for the bit remaining would have required only the scavenge pump anyway. Forget the fact that the CWT tests that attempted to cause an explosion in the mockup models were 100% unsuccessful; they couldn't create a fire or explosion, even flooding the tank with propane and using aircraft ignitors failed to cause the explosion; it took numerous tries and a combination of air injection and various flammable vapor, none of which is found in the 747 fuel system, to eventually cause an explosion, which did not cause the type of catastrophic rupture and failure predicted.

Three operating packs, however, forward of the CWT, produce an attractive heat signature, and the El Al 747 Classic that was about to takeoff turned back to the gate, TWA 800 taking off instead. Thousands saw the streak upward, radar recorded a rapid boat egress from the launch site, hundreds of witnesses were interviewed who saw the same thing, not nearly as easily discounted as attempted in the official explanation. The US had a lot to lose by admitting to a shootdown.

TWA 800 did not simply "blow up," and the CIA video was laughingly unbelievable and tenth rate cartoonish in its defiance of physics and the flight data.

The aircraft was shot down.
 
TTailedTiger
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 2:08 am

That is way too much time to give airlines to retrofit fleets. Safety comes before profits. They should have been forced to slash schedules or fly with full fuel tanks until the entire fleet is outfitted. No one should have to worry if their flight is going to spontaneously explode.
 
GalaxyFlyer
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 4:29 am

I like a good conspiracy story, but it’s a little hard to believe a group of USN sailors shot down an airliner, escaped, then the NTSB, CIA and FBI covered it all up. Hundreds of witnesses told their stories and then shut up. That’s a lot of conspirators in tha act, most of which have no incentive to participate. The USS Vincennes shot down an airliner and the world knew who did it within hours.
 
GalaxyFlyer
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 4:31 am

TTailedTiger wrote:
That is way too much time to give airlines to retrofit fleets. Safety comes before profits. They should have been forced to slash schedules or fly with full fuel tanks until the entire fleet is outfitted. No one should have to worry if their flight is going to spontaneously explode.


It is not a hazard demanding massive disruptions in travel or the economy. The risk was always low and I think the rule unnecessary. Fuel inerting systems have their own problems—cost, failures and flying under MEL relief.

Safety is about probabilities, weighing risk and reward, not absolutes.

GF
 
747Whale
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 4:40 am

GalaxyFlyer wrote:
I like a good conspiracy story, but it’s a little hard to believe a group of USN sailors shot down an airliner, escaped, then the NTSB, CIA and FBI covered it all up. Hundreds of witnesses told their stories and then shut up. That’s a lot of conspirators in tha act, most of which have no incentive to participate. The USS Vincennes shot down an airliner and the world knew who did it within hours.


The notion that the US or the US Navy shot down TWA 800 is without merit, and is both an offensive and poorly thought out outlandish flight of fancy. The US Navy did not shoot down TWA 800.

It was shot down, and it was an error; the individuals who shot it down got the wrong aircraft.
 
strfyr51
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 8:34 am

747Whale wrote:
Dalmd88 wrote:
OneSexyL1011 wrote:
All this because a 747 was shot down.

Yes, I refuse to believe the story of TWA800

Every time I worked on one of the AD related cards I would think, "This will prevent it from exploding when the missile hits." I also don't buy the TWA 800 fuel vapor story. Planes were flying around for decades with this pack/tank combo with zero incidents.

For me these AD's were a money maker so I can't complain.


Anyone who knows the fuel system on the 747 Classic knows that the official accounting of TWA 800 is ridiculous and not true. There wasn't a single peer in the Classic whether captain, f/o, FE, mechanic, or loadmaster who remotely entertained the official story as being true; we all knew better.

The CWT did not rupture internally due to arcing or an overheated fuel pump, particularly as the fuel pumps weren't on and the CWT wasn't in use on that flight. Given that wing tanks hold 230,000 lbs, more than needed for the crossing, CWT fuel was unneeded and for the bit remaining would have required only the scavenge pump anyway. Forget the fact that the CWT tests that attempted to cause an explosion in the mockup models were 100% unsuccessful; they couldn't create a fire or explosion, even flooding the tank with propane and using aircraft ignitors failed to cause the explosion; it took numerous tries and a combination of air injection and various flammable vapor, none of which is found in the 747 fuel system, to eventually cause an explosion, which did not cause the type of catastrophic rupture and failure predicted.

Three operating packs, however, forward of the CWT, produce an attractive heat signature, and the El Al 747 Classic that was about to takeoff turned back to the gate, TWA 800 taking off instead. Thousands saw the streak upward, radar recorded a rapid boat egress from the launch site, hundreds of witnesses were interviewed who saw the same thing, not nearly as easily discounted as attempted in the official explanation. The US had a lot to lose by admitting to a shootdown.

TWA 800 did not simply "blow up," and the CIA video was laughingly unbelievable and tenth rate cartoonish in its defiance of physics and the flight data.

The aircraft was shot down.
. So
OK? So here comes the conspiracy theory. TWA was close to Broke and nearly going Under, (CH-11) TWA800 happens and immediately? They get a WHOLE batch of B757-231's The US NAVY had a training operation going on in Long Island Sound. A Missle was shown to be ascending from a DDG (Guided Missle destroyer) and then the air was raining 747 parts... That is why I believe this is a cover-up plain and simple. I worked with a Lot of EX-TWA Mechanics who ALSO felt that way as well, Most all of them are retired now, but they were damn good at what THEY DID and United was pretty damn happy with them too.
 
747Whale
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Re: What exactly is the fuel-inerting system on 747's?

Wed Feb 27, 2019 10:18 am

The notion that the US military intentionally shot down a US airliner is far fetched and far beyond plausible. Further, there is nothing to support but anecdotal connecting of dots.

Not long prior to the shootdown, the NJ state police recovered a French Mistral missile and launcher, and despite some fanciful NTSB animation (which is inconsistent) that shows the aircraft ascending another 3,000' after its last known altitude of 13,800' (inside the threat envelope for certain man portable missiles), the aircraft was low enough and slow enough to be shot. The hottest heat signature from below isn't the engine, but the packs, which are adjacent to the center wing fuel tank (CWT).

Following the downing of the aircraft, only US Navy personnel and resources were allowed access, and all available commercial craft and operators were excluded from the salvage operation. That it turned into a military salvage operation is not typical, nor what is expected when commercial assets are available and required to be used first.

I absolutely guarantee that had a guided missile frigate been involved in the downing of TWA800, the secret would have been impossible to keep. Operators in the Bin Ladin raid couldn't keep their mouth shut; in fact, they climbed over each other writing books and seeking movie rights, including some false claims as to who was the shooter, so anxious were they to tell their story. Chris Kyle not only "told all," but made up outlandish stories on national television and radio about sitting atop the superdome and killing some 30 Katrina refugees with a sniper rifle. Publicity hungry soldiers cannot keep a secret of that magnitude, and will make things up just to be heard, let alone sitting on it indefinitely. An entire ship and operation that said nothing? Not a chance.

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