Qantas 744 Depressurisation

[Desk Jockey]

Only scary thing is putting the rubber jungle back

[ExSp33db1rd]

Blacksheep said ... .......Hmm, all these hats being taken off to the crew for a wonderful job? Decompression. PNF opens the QRH and begins droning through the SOP that they've rehearsed so often they could do it in their sleep.............

If you have personally Commanded a Boeing 747 through an unplanned emergency descent, I will accept your snide criticism.

I have. Despite the sleepwalking practice, the adrenalin still flows and the lack of precise knowledge of the cause fuels the anxiety.

The crew are trained to do it in their sleep, that's why they did a good job - what's your gripe about that ?

[RRMerlin]

As a customer for the aviation industry's services rather than being involved and a professional metallurgist specialising in high alloy steels, I have had a life-long interest in accident investigation by the aviation industry and I am in no doubt the probable cause of this structural failure will be found. In the meantime we should be thankful that aircraft design, manufacture and crew training have combined to ensure there were no injuries or fatalities.

However, after hearing the latest news items this evening on the Australian media including statements by Qantas executives; I am concerned with the "spin-doctoring" that appears to be underway.

I had contact with the post-accident investigation of Australia's worst rail disaster at Granville NSW in 1977:

Granville rail disaster - Wikipedia, the free encyclopedia

The cause of the accident may be traced back to maintenance cost-cutting by Phillip Shirley; a British "expert" hired by the State Government to "improve" [i.e. significantly reduce the loss or even make a profit] the NSW railway system. Shirley effectively implemented a "bust and fix" maintenance policy and virtually eliminated scheduled preventative maintenance. It took a period of years before the effects of the cost-cutting on track maintenance became apparent. With an impeccable sense of timing, Shirley left the NSW railways not long before the Granville disaster and benefited from political interference in the subsequent inquiry to restrict the amount of blame placed on the Government for the disaster. The subsequent cost of fixing the neglect cost far more than the "savings" achieved by reducing maintenance.

I have a sense of "deja vue" about Qantas and I earnestly hope this incident will make Qantas management take a long, hard look at their maintenance practices, facilities and obligations. It is an old adage that those who ignore the lessons of history are condemned to repeat them. If I were a Qantas executive, I would not want to be seen as Qantas's "Phillip Shirley" and be a contributor to this airline losing its unique status in the aviation industry. From the perspective of a Qantas shareholder, protection of the company's reputation and standing should be the highest priority of the Board along with the long-term survival of the Company. I have grave reservations whether this is the case at the present time.

[Bushfiva]

Found this on net! pretty scary footage!!

With 10 seconds of effort you could have found it in this thread, too.

[Furriskey]

Corrosion

Call me a cynic, but this kind of statement "Our preliminary checks on this indicate there was no corrosion anywhere near where this hole occurred in the aircraft," he told ABC news in Australia." just makes me think that there was corrosion elsewhere of which Qantas were aware.

[pacplyer]

Hi Tech is spot on, imho.

That fairing is not structural, and the boeing CDL may even allow ferry flights with part of it off, not sure, can't remember.

Oxygen bottles or even fire agent tanks exploding are rare, almost unheard of events in aviation (I've never heard of one in flight.) But not impossible due to the possibility of internal tank corrosion. Usually, if there's a thermal expansion problem they will blow out the green "blowout discs" on the side of the fuselage which is their function. Now, they can go off like a rocket in the hangar if tipped over and the brass works get knocked off.... but that's because they aren't secured to anything and the thrust produced by the escaping gas is accelerating your unrestrained, hole-punching newly commissioned "bottle-rocket." But the ship's on board O2 tanks, however, are secured in on board racks aren't they? So If one decides to go into orbit something else must of dislodged it, or it was not secured properly to start with. Pretty unlikely guys if you ask me.

More likely are possible signs of black corrosion on the green zinc chromate where the rivet heads are (dripping downwards) in the photos. It's a common sight on old airplanes in inaccessible locations. On the other hand, it may be a harmless stain and there's no way to tell without a closer inspection.

What is odd about this, to me, is the possibility we are seeing a ULD steel pallet bottom that has been grossly deformed. Many of these containers are steel on the bottom and fastened aluminum on the sides (or in the case of a pallet, just steel.) They are fairly heavy gage on the bottom and FAR regs require the total weight of each individual one to be stenciled on the side for weight and balance calculations. It's surprising to me that an explosive decompression alone could deform such a tough structure if that's what I'm seeing, but clearly it sucked it through the [aft fire curtain] of the [aft lower] cargo compartment to the location it is in now; complete with what you would expect to see, shipping debris, on top of a pallet.

Corrosion or improper repair are the usual suspects in my mind (Ask JAL in tokyo about that.) How many times have you seen an ice bucket quietly leaking into the floor back in galley cart land? How many times have you seen overventing stains behind the lav drain masts?

Note to self: Quit eating those free blue icicles on the lawn every morning at my house under the SID flightpath!

[Litebulbs]

Not an expert on ULD design, so a question. Do they have differential pressure protection. If you have a rapid decompression of the hold, (as part of the complete sealed pressure vessel), how quickly can they disperse their pressure, or could the ULD itself, experience an rapid decompression from a potential weak point, after the initial decompression? OK, it would be a minor event due to its volume, but could it be enough to detach part or all of its wall, allowing the baggage that is clearly seen, time to head toward the fuselage hole?

Or the baggage was just strapped down on a pallet!

[SpannerTwister]

ULD's are not "sealed".

Imagine a (ULD-shaped) box, now remove the front of that box and replace it with a fabric curtain.

Given that (even when it's secured) it's effectively "flapping in the breeze", IMHO, if there was a pressurised container in the ULD that "let go", the excess pressure would firstly blow the front flap around, and secondly rip the front flap off, long before there would be any structural damage to the container.


SpannerTwister

[HotDog]

pacplayer

but clearly it sucked it through the aft pressure bulkhead of the lower forward cargo compartment

There is no lower FWD cargo compartment aft pressure bulkhead on the 747. There is a ziplocked neoprene curtain which reveals the cargo fire bottles and the potable water tanks if you un-zippit. The FWD, AFT and BULK cargo compartments are all within the same pressure vessel as the cabin.

[Blacksheep]

- what's your gripe about that ?

Nothing. Why quote out of context? Or did you stop reading at the end of the opening sentence? You may wish to read post 263 as well.

I am simply saying there is too much dramatisation of this incident in which the aircraft was never in any danger of breaking up or control being lost. Yes it is dramatic to the general public, but from a professional point of view there are far more serious incidents every day that don't produce such a wonderful photo opportunity, but where the pilots truly deserve our admiration. These incidents usually pass unnoticed outside the industry, because there are no photo opportunies, no screaming passengers, no plunging out of the sky and no primary schools to be saved from a fiery end.

The crew, clenched buttocks or otherwise, followed procedures and landed the machine. Now, a rather interesting engineering investigation will follow. Heaven knows, we may even see an NPRM followed by an AD!

Meteorites, space junk, exploding oxygen bottles, golf putters and dead horses not withstanding.

[Litebulbs]

So the bags could just progress toward the hole with the mass flow of air going that way? I was not thinking of the potential decompression of ULD's , just why the bags where were they were. I have also been informed by the other half, about the fabric/plastic flap that covers the opening, so a blond moment from me. Sorry.

[pacplyer]

Litebulbs,

Well I'm hoping a sheet metal mechanic who repairs these things will jump in here and comment. I'm not an expert at anything. Just a has-been. ULD's (Underfloor Loading Devices?) are clanky affairs with poorly fitting thin coke "can" doors on the sides that sometimes blow apart on the ramp just from jet blast and high wind. They have imprecise hinges/curtains etc and are just designed to keep dust off or to keep the customer's contents from shifting. They would just simply blow apart save the frame and the steel bottom which appears as that tin colored "strap" in the photo. (It's amazing to me how golf nuts seem to see putters and golfbags everywhere they go )

A pallet buildup however would have plastic, netting, straps etc and may be what we're seeing here. But in the torn open region; under this missing faring area, IIRC is a pneumatics crossover bay and should not have anything like this in here. Thus our deduction that it got there through the aft wall of the cargo compartment, which is what you'd expect to see if the spars and stringers failed as forensically described by the engineers in previous posts.

But I am no expert. The above post is; as all my post are: my opinions only. I could be wrong about everything; I'm old.

pac - out

[pacplyer]

Thanks hotdog,

I realize it's all one pressure vessel, but structurally I'm trying to describe that aft wall/curtain area that loaders sleep against in Manila when it's hot. You're right it's not a pressure bulkhead, I misspoke.

pneumatics bays are unpressurized as are the gear wells, right? So the bulkhead is further aft. So all it had to do was transverse a fire curtain.

(trying to remember from 18 yrs ago and my books are 7000 miles away.)

Good work hotdog.

[Ex Cargo Clown]

Well I'm hoping a sheet metal mechanic who repairs these things will jump in here and comment. I'm not an expert at anything. Just a has-been. ULD's (Underfloor Loading Devices?) are clanky affairs with poorly fitting thin coke "can" doors on the sides that sometimes blow apart on the ramp just from jet blast and high wind. They have imprecise hinges/curtains etc and are just designed to keep dust off or to keep the customer's contents from shifting. They would just simply blow apart save the frame and the steel bottom which appears as that tin colored "strap" in the photo. (It's amazing to me how golf nuts seem to see putters and golfbags everywhere they go )

A pallet buildup however would have plastic, netting, straps etc and may be what we're seeing here. But in the torn open region; under this missing faring area, IIRC is a pneumatics crossover bay and should not have anything like this in here. Thus our deduction that it got there through the aft wall of the cargo compartment, which is what you'd expect to see if the spars and stringers failed as forensically described by the engineers in previous posts.

But I am no expert. The above post is; as all my post are: my opinions only. I could be wrong about everything; I'm old.

pac - out

It's difficult to discern what is actually in the whole but having seen the "blown-up" picture it appears that the black bag is indeed on a pallet, and is netted (looks like it was netted too loosely BTW) whereas the red bags don't appear to be netted at all, so may well have spilled out of a bin.

An aircraft unit won't decompress as it's not pressurised, the front curtain on it is designed to keep the bags/freight in and dry, nothing else. As for a container "blowing apart". I don't think so.

As for freight coming through the aft wall of Compartment 2. I think this aircraft may have had more problems than just the hole in the fuselage if that had happened

[Litebulbs]

I was not suggesting ULD's are pressurised, but if it was sealed (which it is not, as has been explained apart from fly away kits which are secure all metal bins with locks, or cooled containers) that in a rapid decompression, it would have the potential to be of a higher pressure than the ambient pressure environment around it, which could lead to a rapid equalisation, through a weak point.

However, if the canvas flap just flaps open, then a non event. Hence my apology.

[Ancient Observer]

Douglas Adams contributing from beyond the grave?

Some of the contributions to this thread would have made Douglas Adams proud. Why do some contributors engage hyper-improbability drive before typing in their stuff?

[forget]

Purely as a point of interest - any 747 experts there who could calculate, from the size of the hole and good inflow from operating systems, how fast the cabin would climb. Given an immediate max rate descent what's the highest the cabin got to.

[mono]

I'm with blacksheep here. While the crew were perhaps doing this in anger for the first time, they are trained to do so (an earlier comment from an afronted pilot stated they are trained to do it in their sleep - exactly I say!). As an engineer I am trained to fix airplanes. I don't go patting my self on the back everytime I cure a snag and get the a/c on it's way. Pilots and engineers are not there for when things are going well but for when they go wrong!

Enough thread creep.

What we have here is very interesting from an engineering perspective. It is a failure if the pressure vessel, perhaps originating from a lap joint in what looks like the area of a previous repair. Lap joint scribe lines are a know issue with other Boeing types with (IIRC) at least one example being attributed to manufacture rather than maintenance. Of course the previous maintenance history of the a/c will be checked and I personally wonder what disassembly and prep was required for the initial (scab) repair. There are at least 2 frames missing. Were these replaced at some time and failed at their splices?

Also to further confuse the impact/explosive decompression argument. Some of the structure which has blown outwards does indeed appear to have its outer edges curled inwards!!!!

I await the report with interest>

[lomapaseo]

am intrigued at the relatively low altitude of failure. I can't remember with a -400 when the cabin hits max differential pressure. If it was much less than 8.6psi, then the failure would seem to have occurred rather surprisingly early

That's how oil-canning behaves.

it's a case of residual strength vs buckling. If it was pure over-pressure then your thinking would be correct.

[Phil1980's]

@HotelMode........Well Sir...Aeroplanes have special little things on them that turn the plane and a meteor doing a diagonal fall could hit it I wasn't being sarcy that much just being playfull But I still agree with the meteor idea aswell as others