Qantas 744 Depressurisation
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If the oxygen bottle assembly was only fitted to the aircraft 6 months ago, then who overhauled it and did QANTAS trained engineers fit it or were they contractors working for QANTAS. I ask this as a lot of QF people are under pressure at the moment.
I hardly think anyone wants this thread to turn into irrelevant union-instigated contractor-bashing, so why not start up another thread if you want to go there?
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What's Relevant?
Re-Heat
Sorry if I have offended anyone. But as you stated "as long as it was done to Qantas standards" and that is relevant. I have only heard of an oxygen bottle exploding during charging or through contamination with oil, not while stored. And if this forum has speculated that it was an oxygen problem that led to the hull failure then it would be relevant to find out if incorrect installation was a root cause, and if so by whom. QANTAS is now a global company with maintenance done in many countries. Nothing to do with bashing anyone.
Sorry if I have offended anyone. But as you stated "as long as it was done to Qantas standards" and that is relevant. I have only heard of an oxygen bottle exploding during charging or through contamination with oil, not while stored. And if this forum has speculated that it was an oxygen problem that led to the hull failure then it would be relevant to find out if incorrect installation was a root cause, and if so by whom. QANTAS is now a global company with maintenance done in many countries. Nothing to do with bashing anyone.
I believe QF were the unlucky recipients of a one off event
Trouble with one off events - they have a nasty habit of repeating themselves.
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Thought it might be opportune to explain the oxygen system.
The B744 has a gaseous oxygen system. This was the norm back in the 60s, all aircraft were like this. The oxygen generators appeared in the early 70s, I first saw them on the L1011 where they were standard on the pax system. They are now standard on most aircraft. Unusually the B777 can be seen with both systems depending on the airline.
Anyway back to the B744.
The crew and pax systems are separate. The crew has one or two bottles, the pax side has a row of bottles, the total number depends on the airline fit. All the bottles are filled from one charging point. NRVs separate the crew and pax systems. The pax bottles are all connected to a common main through individual regulators. Loss of one bottle would not affect thesystem, unless the regulator was damaged when the whole system pressure could drain away.
The B744 pax system has two modes, therapeutic and emergency. Therapeutic is selected by a red guarded switch in the flight deck (looks the same as the manual on switch!) A none-surge flow control valve introduces oxygen at about 2psi into the pax supply. Separate masks can be plugged into this main.
If emergency is selected manually, or automatically via a cabin altitude switch, the surge flow control valves introduce oxygen at about 16psi into the same main. This higher pressure opens the PSU doors and allows the masks to drop. Each mask is individually actuated by pulling it down which releases a pin from the supply valve and oxygen starts to flow. The ring main pressure drops to 2 psi after actuation. Oxygen will continue to flow from each actuated mask until the system is switched off.
So, masks are dropped by oxygen pressure (the door latches are not electric)
The whole system is one big ring main.
All the pax bottles feed the same main.
Pulling the mask to your face should be sufficient to pull out the pin, but there is a streamer there that says pull on it.
Oxy generator systems are different in that the doors are opened electrically. Pulling on one mask starts the flow of oxygen to all masks in the same box.
The system cannot be stopped once started.
(Also once it is used it takes forever to replace all the generators).
The B744 has a gaseous oxygen system. This was the norm back in the 60s, all aircraft were like this. The oxygen generators appeared in the early 70s, I first saw them on the L1011 where they were standard on the pax system. They are now standard on most aircraft. Unusually the B777 can be seen with both systems depending on the airline.
Anyway back to the B744.
The crew and pax systems are separate. The crew has one or two bottles, the pax side has a row of bottles, the total number depends on the airline fit. All the bottles are filled from one charging point. NRVs separate the crew and pax systems. The pax bottles are all connected to a common main through individual regulators. Loss of one bottle would not affect thesystem, unless the regulator was damaged when the whole system pressure could drain away.
The B744 pax system has two modes, therapeutic and emergency. Therapeutic is selected by a red guarded switch in the flight deck (looks the same as the manual on switch!) A none-surge flow control valve introduces oxygen at about 2psi into the pax supply. Separate masks can be plugged into this main.
If emergency is selected manually, or automatically via a cabin altitude switch, the surge flow control valves introduce oxygen at about 16psi into the same main. This higher pressure opens the PSU doors and allows the masks to drop. Each mask is individually actuated by pulling it down which releases a pin from the supply valve and oxygen starts to flow. The ring main pressure drops to 2 psi after actuation. Oxygen will continue to flow from each actuated mask until the system is switched off.
So, masks are dropped by oxygen pressure (the door latches are not electric)
The whole system is one big ring main.
All the pax bottles feed the same main.
Pulling the mask to your face should be sufficient to pull out the pin, but there is a streamer there that says pull on it.
Oxy generator systems are different in that the doors are opened electrically. Pulling on one mask starts the flow of oxygen to all masks in the same box.
The system cannot be stopped once started.
(Also once it is used it takes forever to replace all the generators).
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If the rupture in the hull was caused due to some other reason rather than the failure of the oxygen bottle could the turbulence in the breached hull space be sufficient to cause an O2 bottle to become loose and fracture?
If i remember correctly PAX oxygen is an option on 747 , i.e some have the gaseous system but most have oxygen generators. same with some other types i.e A340-300 at least one operator has gaseous.
Flight-Crew Oxygen
Thanks for your clear and succinct overview, Swedish Steve.
I wonder how many aviation people are as surprised as I am to learn that a B747-400 still uses an oxygen ring-main for the whole cabin; a feature I associate with the likes of the B707 and VC10.
One wonders what would have happened if the nearby flight-crew oxygen system had been taken out as a result of the explosion. It also highlights, however, the less than ideal concept of flight crews themselves having to rely on remote bottled oxygen systems, which I believe are still the norm on new types that use oxygen generators for their cabin systems. Fortunately, most types of flight-crew mask can be transferred to a portable (therapeutic) oxygen bottle, no doubt with limited performance. I dare say that crews on many aircraft types are rehearsing the procedure as I write.
As an ex-pilot, my recollection is that recharging (or exchanging) the bottles has always been a potentially hazardous operation. Are safer systems yet available?
I wonder how many aviation people are as surprised as I am to learn that a B747-400 still uses an oxygen ring-main for the whole cabin; a feature I associate with the likes of the B707 and VC10.
One wonders what would have happened if the nearby flight-crew oxygen system had been taken out as a result of the explosion. It also highlights, however, the less than ideal concept of flight crews themselves having to rely on remote bottled oxygen systems, which I believe are still the norm on new types that use oxygen generators for their cabin systems. Fortunately, most types of flight-crew mask can be transferred to a portable (therapeutic) oxygen bottle, no doubt with limited performance. I dare say that crews on many aircraft types are rehearsing the procedure as I write.
As an ex-pilot, my recollection is that recharging (or exchanging) the bottles has always been a potentially hazardous operation. Are safer systems yet available?
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Confused systems engineer
Interesting Media Release. No mention of exploded aircraft oxygen cylinders or shrapnel in the aircraft cabin, only that they are examining the oxygen systems and they have retained some components and "parts of components".
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I wonder how many aviation people are as surprised as I am to learn that a B747-400 still uses an oxygen ring-main for the whole cabin
I know that when our B767 (with generators) fly certain routes they have to carry loads of portable bottles for this reason.
CVR Misses capturing Event
Pilots' reaction to explosion missing from tape | theage.com.au
my exerpts from article are;
In some of the previous explosive decompressions the analysis of the CVR could distinguish between a bomb (overpressure followed by outflow) and a pure fuselage rupture (outflow). Additional factors include reverberation (reflected waves off bulkheads) and structure borne dialation waves. Too bad in this case that the info is overwritten. I was surprised about the time frame that the CVR was running after the event.
I am never sure about news articles and whether they are paraphrasing what is said or whether they are actual quotes. But the quoted article above seems to leave open the possibility that the Oxygen tank might not have ruptured and simply tore loose out the hole afterwards.
my exerpts from article are;
..........."Unfortunately, the standard two-hour recording, which works on an endless loop principle, did not contain the de-pressurisation event," senior ATSB investigator Neville Blyth told a media conference in Manila.
"The oldest part of the recording on the cockpit voice recorder commenced after the descent and diversion to Manila, so the event itself appears to have been overwritten."
He said the audio could yet be "very, very useful" - including in relation to examining airflow. "There is a surprisingly large amount of information that can be obtained from acoustic spectrum analysis, if indeed we have a recording of the event," Mr Blyth said.
"The oldest part of the recording on the cockpit voice recorder commenced after the descent and diversion to Manila, so the event itself appears to have been overwritten."
He said the audio could yet be "very, very useful" - including in relation to examining airflow. "There is a surprisingly large amount of information that can be obtained from acoustic spectrum analysis, if indeed we have a recording of the event," Mr Blyth said.
Mr Blyth acknowledged that the "most likely explanation for the absence of the cylinder" was that it was blown through the fuselage.
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My comments about the valve and pieces of the cyilinder were quoted from a CNN video of a interview with the lead investigator. I can't find the video - but here is the story: Valve in oxygen cylinder the culprit in 747 explosion - News - Travel
""We recovered a valve from an oxygen cylinder," Neville Blyth, a senior investigator with the Australian Transport and Safety Bureau, told a news conference yesterday. "It is likely that that valve is from the missing cylinder."
"The recovered valve is to be subjected to a forensic engineering examination at the ATSB's Canberra laboratory, where the cockpit voice recorder and flight data recorder are being downloaded. Maintenance records, including those for the oxygen supply system, are being scrutinised.
The valve had been found in the passenger cabin a couple of metres away from the bank of about six cylinders.
"The cabin floor of the aircraft has a hole approximately 20 centimetres in diameter above the location of the cylinders," Mr Blyth said. Asked if other 747s could have restrictions placed on them, Mr Blyth said a CASA representative was in Manila monitoring the investigation. This would allow for "any further safety action considered necessary", in addition to Qantas inspecting the oxygen systems on its 747 fleet, which is to happen by Friday."
""We recovered a valve from an oxygen cylinder," Neville Blyth, a senior investigator with the Australian Transport and Safety Bureau, told a news conference yesterday. "It is likely that that valve is from the missing cylinder."
"The recovered valve is to be subjected to a forensic engineering examination at the ATSB's Canberra laboratory, where the cockpit voice recorder and flight data recorder are being downloaded. Maintenance records, including those for the oxygen supply system, are being scrutinised.
The valve had been found in the passenger cabin a couple of metres away from the bank of about six cylinders.
"The cabin floor of the aircraft has a hole approximately 20 centimetres in diameter above the location of the cylinders," Mr Blyth said. Asked if other 747s could have restrictions placed on them, Mr Blyth said a CASA representative was in Manila monitoring the investigation. This would allow for "any further safety action considered necessary", in addition to Qantas inspecting the oxygen systems on its 747 fleet, which is to happen by Friday."
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Some reports quote passengers who pulled the masks a bit too firmly and pulled them out of the ceiling. There are also reports of some masks not dropping and flight attendants having to pull them down. My guess is that masks failing to drop might be related to no oxygen pressure - or low pressure further away from the supply - are they all on one line/ring ?
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Read The Thread Before Posting!
Originally Posted by Swedish Steve Post #646
The pax bottles are all connected to a common main through individual regulators....The whole system is one big ring main.
Originally Posted by infrequentflyer789 Post #654
masks-are they all on one line/ring ?
I'm beginning to understand why the moderators cull these popular threads so hard.
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With regards to pax oxy... getting a little bit off topic here, but oh well.
It was mentioned earlier that there's a need for explanation as to how much to pull on the oxygen mask/lanyard/tubing (whatever you want to call it).
I recall during my intial training years ago, my particular airline was quite specific about it being one (and ONLY one) firm pull... it was described to me as being 'about the same as one of those pull-chain lightbulbs'. Of course, not many people probably remember those now!!
Unfortunately, a lot of cabin crew out there dont know (or care) WHY the oxygen demo is (mostly) taught this way- not two yanks on the mask, ONE firm pull. So they continue to either 'pull-pull-yank' or just hold the tubing up and place the mask over their face, which further confuses the issue.
Perhaps a little reminder on the oxygen system is needed for the FAs of today?? Just a thought...
It was mentioned earlier that there's a need for explanation as to how much to pull on the oxygen mask/lanyard/tubing (whatever you want to call it).
I recall during my intial training years ago, my particular airline was quite specific about it being one (and ONLY one) firm pull... it was described to me as being 'about the same as one of those pull-chain lightbulbs'. Of course, not many people probably remember those now!!
Unfortunately, a lot of cabin crew out there dont know (or care) WHY the oxygen demo is (mostly) taught this way- not two yanks on the mask, ONE firm pull. So they continue to either 'pull-pull-yank' or just hold the tubing up and place the mask over their face, which further confuses the issue.
Perhaps a little reminder on the oxygen system is needed for the FAs of today?? Just a thought...
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Infrequent flyer
Swedish Steve
I will try and explain more slowly. Oxygen pressure opens the latches and the panels in the PSU fall open. The masks are now sitting on nothing and will fall when gravity lets them.
The masks and the coiled up plastic tube are a snug fit in the boxes. Occasionally they will not drop by themselves and need a nudge. It really depends on how well they are packed. I personally find it quite difficult to roll up 4 masks and stow them in a box in situ, but it beats taking the boxes out on a transit!
My guess is that masks failing to drop might be related to no oxygen pressure - or low pressure further away from the supply
introduce oxygen at about 16psi into the same main. This higher pressure opens the PSU doors and allows the masks to drop.
The masks and the coiled up plastic tube are a snug fit in the boxes. Occasionally they will not drop by themselves and need a nudge. It really depends on how well they are packed. I personally find it quite difficult to roll up 4 masks and stow them in a box in situ, but it beats taking the boxes out on a transit!
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A thought....
The oxygen system is there in case of an emergency.... right?
Bird strike up front going through the window or the front bulkhead.
A window blowing out through a fault or a pax going crazy.
A fault in a door, like a cargo door blowing out.
A structural failure (with the 737 cabriolet as an extreme).
So the oxygen system is there as a backup/emergency system for such rather rare occurrences.
In other words, we thought we had two low-probability events: a rapid decompression AND an oxygen system failure, before we had a real problem
But maybe nobody did the sums for the case where the oxygen system itself was going to be at the origin of the decompression..... ?
The oxygen system is there in case of an emergency.... right?
Bird strike up front going through the window or the front bulkhead.
A window blowing out through a fault or a pax going crazy.
A fault in a door, like a cargo door blowing out.
A structural failure (with the 737 cabriolet as an extreme).
So the oxygen system is there as a backup/emergency system for such rather rare occurrences.
In other words, we thought we had two low-probability events: a rapid decompression AND an oxygen system failure, before we had a real problem
But maybe nobody did the sums for the case where the oxygen system itself was going to be at the origin of the decompression..... ?
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Hope this isn't a wind-up
SLF - Self Loading Freight, i.e. you and I.
MEL - Minimum Equipment List, a list of items that the aircraft can still be dispatched with if not functioning.
SLF - Self Loading Freight, i.e. you and I.
MEL - Minimum Equipment List, a list of items that the aircraft can still be dispatched with if not functioning.