Hello, I'm writing a thesis on this subject and been incredibly curious as too why the system shuts off when its on the ground. I don't know if you ended up getting an official answer on why, but through my line of work I have access to the NG and Max AMM's in here it states the official procedure the system follows and why it shuts off on the ground. It is not to protect ground crew from passing out in the wheel well from low oxygen content AMM, SDS ATA 47 When the airplane lands, the NGS changes from the high-flow mode to the low-flow mode. The NGS operates in the low-flow mode on the ground for 10 minutes. When the left Flow Control and Shutoff Valve (FCSOV) closes before 10 minutes, the NGS does not start again when the FCSOV opens. When the airplane completes 10 minutes, the system goes to the cooldown mode. There is no flow through the system during the cooldown mode. The NGS cooldown mode prevents damage to the NGS heat exchanger. Ram air flow will not go to the heat exchanger. This prevents a thermal shock from a fast cooldown. The NGS cooldown mode keeps the NGS shutoff valve (SOV) open and closes the Over Temperature Shutoff Valve (OTSOV). This lets system pressure go to the Ram Air Valve (RAV) to keep the valve closes. There is no ram air flow at this time. So from this system description and experience of changing the heat exchanger followed my a stationary system test. I believe it is to protect both the ASM and heat exchanger from overheating, since ram air flow is practically zero when on the ground
Thanks Chris I now have a much better understanding of NGS,that was the best NGS explanation I've experienced. I think the history of the system was really enlightening. You spent ages preparing this and your efforts are greatly appreciated. BTW Matthijs could be onto something,why wouldn't the NGS 'exhaust' potentially fill the wheel well with low oxygen content air? It is located near the wheel well. The 'exhaust'would be potentially lighter than the surrounding air,as I believe,O2 is heavier than N2.Anyone entering the wheel well could be asphyxiated until they fell to the floor. Of course,as you point out,on ground is a dangerous phase and if packs run they cause heat,but paradoxically,are prevented from powering the NGS to obviate the danger they created by running in the first place! Best wishes from Paul.
Hi Paul, thanks for your kind comments. I still don’t go for the idea that NGS should be switched off at the only time the two previous explosions occurred just in case the exhaust pooled somewhere. If that was a risk they could have ducted it somewhere safely away from the wheel-well, then problem solved. Such a mystery!
Actually it's the opposite - n2 is very slightly heavier at standard temperature and pressure but they're very close (1.25 vs 1.23). Unless the exhaust was significantly hotter that the air and the air was completely still, no wind, etc. it won't be a problem
737NGS is much simpler than 787NGS. 787NGS (bleedless)has to provide inerting capability to all 3 fuel tanks. 737NGS content is a good introduction to the world of fuel inerting systems for those commercial airplanes. The background on the FAA requirements is spotted on and well balanced regarding technical aspects of the technology.
Chris, I wish I could have the chance to meet you in person eventually to thank you for the work u put in these series of videos and the extraordinary efficient result you got. I am going through the CU process and can't imagine a better way to complement my learning on 737 systems. Thank you.
@@ChrisBrady737 if we do meet expect me to ask for a picture with you, youre becoming quite famous among my peers! Now, seriously amazing job Chris, extremely helpful. Thank you
44:50 While I don't _know_ anything about this subject I do have one bit of speculation to offer: I browsed a copy of the Inert Gas System chapter of the 737-NG AMM that I found floating around on the internet and noticed it puts a lot of emphasis on the danger of breathing the oxygen-depleted air produced by this system. In particular, a leak in the NGS or nitrogen-enriched air distribution lines into any enclosed (or partially enclosed) compartment accessible by ground crew could create a rather insidious hazard.
Whilst that is of course a possibility, the NGS would be operating in the wide open space on the ramp where the by-products would quickly be mixed with ambient air. If the aircraft was ever in a hanger the system could be deactivated quite easily. I personally doubt that is the reason but who knows?
@@ChrisBrady737 Well the concern would be for spaces inside the airplane where leaking nitrogen-enriched air might have the opportunity to accumulate, e.g. the AMM warns to "not go into the main wheel well area more than to waist level" while NGS is operating. The only alternative concern I can think of is fuel vapours in the ullage air being continuously vented overboard while NGS is operating, though I have no idea if the quantity is enough to be relevant in any way. Anyway, this is all just idle speculation from me. Let's hope someone shows up with more concrete information!
Excellent video! Easy to understand and makes everything clearer, only sometimes the stutter made me rewind a little bit every now and then. All in all, thank you Good Sir!
Really enjoyed this vid. I didn't get this kind of explanation is systems training. Thank you for your effort and keep up the good work. Cheers from across the pond!
Congratulations! Your job is excellent and the level of information is unmatchable and most important accurate! Please continue your great job you are helping a lot of us !
I also do not know anything about the subject, so here I am watching this amazing video. I speculate the system cannot be operated on the ground because no temperature regulation can be provided on the ground due to no ram air available and the membrane can be damaged by the elevated temperature.
That was my guess too, that it has something to do with temperature and less ability to keep the units cool on the ground. I know medical oxygen generators/nitrogen scrubbers get surprisingly warm when they're in use. I assume the NGSs heat up too when in use?
I think you answered your own question as to why NGS isn't operative on Ground , It requires ram air cooling , It might be very hard to keep the system cool without Ram Air.
Yet another excellent video, Chris. Thank you for all the work you put into preparing these. I'm just a layman but I really do appreciate your highly-detailed analysis of the plane and its systems. As for why Boeing engineers decided against the tank inerting system operating while the plane is on the ground... Do you know if the fuel intakes of the 737 have check valves against the release of ullage gases at the beginning of the refueling operation? A plane's landing is generally followed by a refueling operation, within a half-hour or less, right? All I can surmise is that since the inerting system works overtime during descent, refuelers could potentially be exposed to a release of oxygen-deficient ullage gas while preparing to hook their fuel pipe onto the aircraft. Is turning the tank inerting system off on landing perhaps some kind of compromise between the safety of the aircraft itself and that of the people servicing it?
Yes there is a check valve at the refuelling point, if for no other reason than to stop a spillage as the refuelling point is under the wing not on top!
Maybe it doesn’t operate on the ground due to air quality problems? There will be a lot more particulate matter and pollutants in the air in the ground, which are going to shorten the life of the filter.
A couple of the other viewers suggested that the reason could be that as there is no ram air on the ground the system would be prone to overheating. this seems to me the most likely reason.
Hello capt.. Thanks a lot once again for an amazingly well researched and informative video. I have a small doubt about what you have mentioned about the vents. So, what I understood is that there is a check valve so that no air from the vents should enter the centre tank as the aircraft descend. That valve only allows the fuel to be overthrown from the vent. But when the NGS is not operational and the MEL does not stop us from using centre tank, how is the centre tank vented and with that I mean how the pressure is equalised. Thanks alot Capt for your efforts and time.
It is a bit complex to explain briefly here but suffice it to say that when the NGS is OFF (eg system inop or on-ground, fire or smoke detection, centre tank refuelling, overpressure or overtemp etc) the NGS controller commands the NGS Pressure Regulating and Shutoff Valve (PRSOV) to close and the centre tank vents as normal. The cross vent check valve will also open.
Could the NGS not operating on the ground be due to an assumption that the ullage in the center tank should already be inert from when the plane last wasn't on the ground?
I don't think that is a safe assumption, especially if the aircraft has not flown for a while. There have been a couple of fuel tank explosions whilst the aircraft has been on the ground so it seem like an oversight to me.
Hello, I'm writing a thesis on this subject and been incredibly curious as too why the system shuts off when its on the ground. I don't know if you ended up getting an official answer on why, but through my line of work I have access to the NG and Max AMM's in here it states the official procedure the system follows and why it shuts off on the ground. It is not to protect ground crew from passing out in the wheel well from low oxygen content
AMM, SDS ATA 47
When the airplane lands, the NGS changes from the high-flow mode to the low-flow mode. The NGS operates in the low-flow mode on the ground for 10 minutes. When the left Flow Control and Shutoff Valve (FCSOV) closes before 10 minutes, the NGS does not start again when the FCSOV opens. When the airplane completes 10 minutes, the system goes to the cooldown mode. There is no flow through the system during the cooldown mode.
The NGS cooldown mode prevents damage to the NGS heat exchanger. Ram air flow will not go to the heat exchanger. This prevents a thermal shock from a fast cooldown. The NGS cooldown mode keeps the NGS shutoff valve (SOV) open and closes the Over Temperature Shutoff Valve (OTSOV). This lets system pressure go to the Ram Air Valve (RAV) to keep the valve closes. There is no ram air flow at this time.
So from this system description and experience of changing the heat exchanger followed my a stationary system test. I believe it is to protect both the ASM and heat exchanger from overheating, since ram air flow is practically zero when on the ground
Mystery solved! Thank you for the information.
Agree, that's also my guess
I know one thing I will check on my walk around tomorrow! Thanks Chris. Amazingly detailed presentation. More to come soon? I do hope so
My pleasure Daniel. Yes, more videos to come.
Really love this episode with the mix of origin of the system and then explanation of how it works !
Thank you!
Thanks Chris I now have a much better understanding of NGS,that was the best NGS explanation I've experienced.
I think the history of the system was really enlightening.
You spent ages preparing this and your efforts are greatly appreciated.
BTW Matthijs could be onto something,why wouldn't the NGS 'exhaust' potentially fill the wheel well with low oxygen content air?
It is located near the wheel well.
The 'exhaust'would be potentially lighter than the surrounding air,as I believe,O2 is heavier than N2.Anyone entering the wheel well could be asphyxiated until they fell to the floor.
Of course,as you point out,on ground is a dangerous phase and if packs run they cause heat,but paradoxically,are prevented from powering the NGS to obviate the danger they created by running in the first place!
Best wishes from Paul.
Hi Paul, thanks for your kind comments. I still don’t go for the idea that NGS should be switched off at the only time the two previous explosions occurred just in case the exhaust pooled somewhere. If that was a risk they could have ducted it somewhere safely away from the wheel-well, then problem solved. Such a mystery!
Actually it's the opposite - n2 is very slightly heavier at standard temperature and pressure but they're very close (1.25 vs 1.23). Unless the exhaust was significantly hotter that the air and the air was completely still, no wind, etc. it won't be a problem
Hi Chris, thank you for the video, I'm a young engineer on NGS and this video provides me a lot of inspirations! Thank you for the wrok :)
That is great to hear, glad the video was helpful.
737NGS is much simpler than 787NGS. 787NGS (bleedless)has to provide inerting capability to all 3 fuel tanks. 737NGS content is a good introduction to the world of fuel inerting systems for those commercial airplanes. The background on the FAA requirements is spotted on and well balanced regarding technical aspects of the technology.
Thank you for your comments.
Chris, I wish I could have the chance to meet you in person eventually to thank you for the work u put in these series of videos and the extraordinary efficient result you got. I am going through the CU process and can't imagine a better way to complement my learning on 737 systems. Thank you.
That is very kind of you. Perhaps our paths will cross one day. Best of luck with your command.
@@ChrisBrady737 if we do meet expect me to ask for a picture with you, youre becoming quite famous among my peers! Now, seriously amazing job Chris, extremely helpful. Thank you
44:50 While I don't _know_ anything about this subject I do have one bit of speculation to offer: I browsed a copy of the Inert Gas System chapter of the 737-NG AMM that I found floating around on the internet and noticed it puts a lot of emphasis on the danger of breathing the oxygen-depleted air produced by this system. In particular, a leak in the NGS or nitrogen-enriched air distribution lines into any enclosed (or partially enclosed) compartment accessible by ground crew could create a rather insidious hazard.
Whilst that is of course a possibility, the NGS would be operating in the wide open space on the ramp where the by-products would quickly be mixed with ambient air. If the aircraft was ever in a hanger the system could be deactivated quite easily. I personally doubt that is the reason but who knows?
@@ChrisBrady737 Well the concern would be for spaces inside the airplane where leaking nitrogen-enriched air might have the opportunity to accumulate, e.g. the AMM warns to "not go into the main wheel well area more than to waist level" while NGS is operating. The only alternative concern I can think of is fuel vapours in the ullage air being continuously vented overboard while NGS is operating, though I have no idea if the quantity is enough to be relevant in any way. Anyway, this is all just idle speculation from me. Let's hope someone shows up with more concrete information!
Absolutely, I would love to know the reason. All good theories on your part though, thank you.
Excellent video! Easy to understand and makes everything clearer, only sometimes the stutter made me rewind a little bit every now and then. All in all, thank you Good Sir!
I am glad you found it useful, thanks for watching.
Really enjoyed this vid. I didn't get this kind of explanation is systems training. Thank you for your effort and keep up the good work. Cheers from across the pond!
My pleasure Bryan, glad you found it useful.
Congratulations! Your job is excellent and the level of information is unmatchable and most important accurate! Please continue your great job you are helping a lot of us !
Thank you for your kind comments. Please tell your colleagues.
@@ChrisBrady737 I will definitely tell !!
I also do not know anything about the subject, so here I am watching this amazing video. I speculate the system cannot be operated on the ground because no temperature regulation can be provided on the ground due to no ram air available and the membrane can be damaged by the elevated temperature.
That is a great theory. I think you might have got the reason
That was my guess too, that it has something to do with temperature and less ability to keep the units cool on the ground. I know medical oxygen generators/nitrogen scrubbers get surprisingly warm when they're in use. I assume the NGSs heat up too when in use?
Another brilliant vid, thx so much for doing these!!
Thanks Mike, my pleasure.
Excellent. So many questions answered
My pleasure, glad you found it useful.
Exceptional! I watch all your videos and I don’t even fly the 737.
😂 Thank you, maybe they will inspire you to try the 737. All the best
Excellent presentation, thank you.
Thank you, glad you enjoyed it.
I think you answered your own question as to why NGS isn't operative on Ground , It requires ram air cooling , It might be very hard to keep the system cool without Ram Air.
Very possibly
Yet another excellent video, Chris. Thank you for all the work you put into preparing these. I'm just a layman but I really do appreciate your highly-detailed analysis of the plane and its systems.
As for why Boeing engineers decided against the tank inerting system operating while the plane is on the ground... Do you know if the fuel intakes of the 737 have check valves against the release of ullage gases at the beginning of the refueling operation? A plane's landing is generally followed by a refueling operation, within a half-hour or less, right? All I can surmise is that since the inerting system works overtime during descent, refuelers could potentially be exposed to a release of oxygen-deficient ullage gas while preparing to hook their fuel pipe onto the aircraft. Is turning the tank inerting system off on landing perhaps some kind of compromise between the safety of the aircraft itself and that of the people servicing it?
Yes there is a check valve at the refuelling point, if for no other reason than to stop a spillage as the refuelling point is under the wing not on top!
Thank you for sharing all those information.
My pleasure
Thank you captain well done 👍
You are welcome
Very interesting story, thank you for sharing that!
My pleasure, thanks for watching
Excellent!!! Thanks Chris
My pleasure!
Maybe it doesn’t operate on the ground due to air quality problems? There will be a lot more particulate matter and pollutants in the air in the ground, which are going to shorten the life of the filter.
A couple of the other viewers suggested that the reason could be that as there is no ram air on the ground the system would be prone to overheating. this seems to me the most likely reason.
Hello capt.. Thanks a lot once again for an amazingly well researched and informative video. I have a small doubt about what you have mentioned about the vents. So, what I understood is that there is a check valve so that no air from the vents should enter the centre tank as the aircraft descend. That valve only allows the fuel to be overthrown from the vent.
But when the NGS is not operational and the MEL does not stop us from using centre tank, how is the centre tank vented and with that I mean how the pressure is equalised.
Thanks alot Capt for your efforts and time.
It is a bit complex to explain briefly here but suffice it to say that when the NGS is OFF (eg system inop or on-ground, fire or smoke detection, centre tank refuelling, overpressure or overtemp etc) the NGS controller commands the NGS Pressure Regulating and Shutoff Valve (PRSOV) to close and the centre tank vents as normal. The cross vent check valve will also open.
Got it Capt… thanks a lot once again..
Could the NGS not operating on the ground be due to an assumption that the ullage in the center tank should already be inert from when the plane last wasn't on the ground?
I don't think that is a safe assumption, especially if the aircraft has not flown for a while. There have been a couple of fuel tank explosions whilst the aircraft has been on the ground so it seem like an oversight to me.
@@ChrisBrady737 Not saying I _agree_ with that assumption - just that it could've been a potential justification offered when designing the system.
very interesting... seems a bit silly since it doesnt work on the ground or with the wings, but hey..
Always brilliant always
Thank you, much appreciated