Qantas 747 oxygen tank rupture 7

[hokie66]

Any thoughts from the aero guys about the incident that happened last week?

 

[prost]

oxygen tank blew, right?

 

[prost]

Why are there oxygen tanks on an aircraft that undoubtedly has an on board oxygen generator? Backup?

 

[MikeHalloran]

I thought they used pyrotechnic oxygen generators; no tank, no piping system.





Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

There are a number of oxygen cylinders in the hold, one exploded, parts of it came up through the cabin floor. A fairing in front of the wing came off, and some control systems were damaged. No injuries. Plane was enroute from Hong Kong to Melbourne, pilot made emergency landing in Manila.

 

[prost]

Yes, but why were there oxygen tanks on the flight? I thought oxygen tanks were taken off passenger airplanes after the Valujet Flight 592 crash in 1996. Obviously not. (please don't beat me up about this not being a flight with an American carrier--everybody's airplanes are hostage to every other countries' regulatory authorities, lots of times the FAA imposes rules that all other countries' carriers that want to fly to the US have to obey, and vice versa.).

 

[bf109g]

Crew oxygen is stored in cylinders with lines going to the flight deck. Standard procedures call for donning of the mask when one man of a two man crew leaves the flight deck. Generators won't work for this applicaton.

It will be interesting to see if the cylinder losing the regulator caused the hole or if the cylinder lost it as it hit something else departing the airplane. Rule #1 in these types of incidents is to never take what the media says as gospel.

 

[rb1957]

at this stage all we know is there is a hole in the plane near where the O2 tanks are stored. note, these are not cargo, like on Valujet, but part of the airplane's systems. we have some reason to suspect the O2 tanks, one "seems" to be missing, fragments "could" be in the cabin.

but did a tank explode ? and more importantly, why ? these questions can only be answered by a detailed investigation.

question came to my mind ... why do we still use metal tanks ? wouldn't this be a good application for composites ?

 

[israelkk]

Composite tanks still need inside metal liner for sealing and the nozzle will still be a metal.

 

[inertia4u]

Some Pictures for you folks.

-----
Nert

 

[inertia4u]

Sorry,

File is about 1 meg in size.



-----
Nert

 

[berkshire]

The interesting questions now will be , When was the defective cylinder last hydro'd and how many fill, discharge cycles had it done?
B.E.

 

[rb1957]

or was "something" added to it ?

 

[FieldTeam]

747-400 has provision for up to 21 high pressure (1850psi/114cfm)passenger O2 system. Chemical system was considered, but the gaseous system won out, allowing more flexability for emergency descent.
The O2 bottles are located in the forward cargo bay and each are equipped with a frangible rupture disc (among other components such as gauge and SOV).
The O2 system cylinders can be added or reduced depending on emergency descent profile for the route planned, saving weight.
O2 distribuion (free flowing, non free flowing and the capability to shut off O2 to areas where it is not needed) is per each customers requirement.
This system is very similar to previous 747's.

Hydrostatic requirements for high pressure cylinders is every 5 years hydro and internal inspection. I do not believe there is a fill/discharge cycle limit to these components.

It's very rare for a tank like this to rupture on its own if inspection intervals are being kept. Filling with other than O2 would most likely lead to an instant failure (explosion) and over filling would blow the disc. All the bottles are cascaded together, so the problem is in the one bottle that failed (assuming the SOV was open).

Mounting of the bottle, so that it was not secure and was damaged to the point of failure or a bottle that was dropped and had an inpending failure are the most likely reasons for failure...if the bottle failure is the sole excuse.
Something coming loose and damaging the bottle is another.

 

[GregLocock]

"Filling with other than O2 would most likely lead to an instant failure (explosion)"

Que?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[thruthefence]

There was an incident awhile back, and as I recall it was Quantas, an Australian carrier, where new servicing carts were ordered, and someone configured an O2 cart with nitrogen bottles. I remained in service for some time, actually servicing aircraft. Luckily no emergency occurred. A clue should be O2 bottles are green, Nitrogen bottles are black, not to mention the Bodging of the hoses needed to "make it work".

( It was Quantas )

found a link:

http://www.avweb.com/avwebflash/news/NitrogenUsedToFillAircraftOxygenSystems_196776-1.html

google "oxygen cart nitrogen cart mix up"

 

[rb1957]

sorry, but it's QANTAS ... no U

 

[FieldTeam]

Sorry>
I should have stated filling with anything that would cause the bottle to fail would most likely cause failure instantly (hydrocarbons). Oxygen is not too forgiving.
Inert gasses (like N2) would contaminate the system, but most likely not cause failure, as shown in the last two posts.

Another line of thought could be a faulty pressure transducer which is installed after the SOV but before the regulator. An electrical fault could cause an explosion. Didn't they find one of the valves in the passenger compartment?

 

[israelkk]

I am not familiar with commercial aerospace regulation but for military and space missions a proper design of a pressure vessel should avoid catastrophic rupture of the vessel. Using fracture mechanics crack propagation analysis It has to be designed for "Leak before Break" if is made of ductile material of to show that a critical crack will never occur during service life. If it was ruptures and didn't stay in one piece then it either didn't designed and tested to prove "Leak before Break" or it was designed as brittle but had critical size cracks that inspection failed to find.

See MIL-STD-1522A STANDARD GENERAL REQUIREMENTS FOR SAFE DESIGN AND OPERATION OF PRESSURIZED MISSILE AND SPACE SYSTEMS.

http://assist.daps.dla.mil/docimage...F6B6B2DC5297A&jsessionid=06305821986d66a59c3d

 

[FieldTeam]

Of interest:
747-400-FTD-35-05001
originated 31-JAN-2005
last revised 09-JAN-2006

747-400 airplanes equipped with composite oxygen cylinders in the passenger oxygen systems that are installed in the ceiling area of the forward cargo compartment.

During production an interference condition was found between forward cargo compartment ceiling mounted passenger oxygen cylinders and the bottom of seat tracks above the cylinders. The interference condition has been checked for on some airplanes delivered with composite oxygen cylinders and some chafing damage has been reported.

This condition is the result of the larger diameter of the composite oxygen cylinders.

Boeing introduced composite oxygen cylinders for a weight savings.

Final corrective action will include replacement of PN B42365-1 composite cylinders with PN 801307-00 steel cylinders in forward cargo compartment ceiling areas and the addition of warning placards at the ceiling locations to prohibit installation of composite oxygen cylinders. A schedule for production and retrofit changes has been established. Production will be changed in-sequence to only steel cylinders in the ceiling area of the forward cargo compartment starting at LN 1375 (May 2006 delivery). Production has already been changed out-of-sequence in December 2004. Boeing released service letter 747-SL-35-022 on 1 April 2005 and released USG category service bulletin 747-35-2118 on 6 January 2006 for in-service airplanes.