OF COURSE the cargo (lower lobe) is pressurized. Otherwise there would be a pressure differential across the flat floor, tending to circularize it (as we saw 33 years ago in the DC-10 cargo door blowouts!)

By maintaining near-zero delta P on the floor -

o Upper lobe skin is in pure tension
o Lower lobe skin is in pure tension
o Floor is in pure tension, preventing the "kink" between the two from bulging out! :ok:

OK, a stupid question - why shouldn´t the lower lobe be pressurized to a higher pressure? It has to carry bending loads due to its own weight and the weight of passengers, seats, galleys/lavatories and cargo placed on it... pressurizing the underbelly to a higher pressure would help with that...

This accident may be completely irrelevant to normal operations. Wait and see what they find. I believe overpressure safety devices must be disabled for this test, and with that someone may have screwed up and gone well above the design pressure diff. Human error is the more common cause of accidents in the air compared to mechanical failure, why should it be any different on the ground?

Not so stupid - structurally that idea makes sense, IMHO.

But the added systems complexity (trying to compensate for zero g, +2 g, full pax, unloaded etc.) seems to make the cure worse than the disease.

Quite a long time ago a Lockheed JetStar (owned by Mobil Oil) was undergoing a hull pressure test, wherein the ultimate pressure reached 21psi, before failure.
The fuselage was quite a sight, and the aeroplane was sent back to Lockheed, where the wing was demated, and attached to a brand new fuselage.
A not inexpensive project, to say the least.

Lockheed paid, IIRC.

A tough 'ole bird, the JetStar...:ooh:

Barit,

agree for the skin, not for the floor. Some portions of the floor are in compression (for the XX delta PSI load case). I am toalikng aobut floor as floor beams havin the upper chord, lower chord and the web.

Some of the upper chords do see compression for the pressure case.

HotDog, indeed. And John Barry Smith did not stop at those three. The China Airlines 747 in-flight breakup off Taiwan in May 2002 was the occasion of his latest sleuthing.

Malaysia Airlines is due to take delivery one of two new freighter at the end of March. It could be one of theirs

Mike Rudder
I have seen a photo of the first B747-400F for MASkargo flying at Seattle PAE, so it is not that one. The pressure test l am sure will be done before it reaches the flight line.
This is what was printed in a Seattle newspaper.
The worker said the plane is being built for a customer in China.
The 747-400 was undergoing what's called a "high blow" pressurization test when the accident occurred, the worker said.
The pressure inside the plane was about 3 pounds per square inch, he said.:uhoh:

If it was only at 3psi it was waaaay short of the 'high blow' figure:eek:

Anyway, dead easy to fix, just graft on a complete section 41:ok:

Indeed. 200 mb differential? The pressure in cruise is what, 750 mb? This meant that the door would blow at 550 mb outside, meaning below 5000 metres... unless the pressurization is started gradually after takeoff instead of at 2400 metres, in which case 200 mb differential would be reached lower than 5000 metres! A cargo plane exploding on climbout...

Sure, these are beams after all, and the pax/cargo loading creates bending stress (compression in the top chord, tensile in botton) whether pressurized or not. These stresses add algebraically to the pressurization (tensile) stresses. Whether the summation of compression & tension in the top chord of the floor beam is ultimately positive or negative must depend on the individual design.

Perhaps there was a nose latching error prior to the test, or incorrect installation of the nose latches, or manufacturing defect in the nose latches.

From what i can see this is a test Boeing make on all aircraft out of production. So it failed the test - surely thats the reason for the test in the first place. All this does is prove the test was worth doing.
Boeing far exceed Airbus at speed and quality of structrual repairs and hopefully the operator will get an aircraft as good as they expected without too long a delay.

Barit1:

Right on the spot.

Mr @ Spotty M:

High blow test is at 1.5xdelta_Pi = 13 psi (app)

I agree with you, there must be a reason why they carry out the test in the first place...

Do other aircraft manufacturers carry out similar tests? anyone who knows?

Founder and Swedish:

Main reason is to see if everything "fits" fine (MCD including!).

Second, maybe more important thing, is to reinforce the structure by preloading it. This procedure should give better fatigue life. Sadly, this was discovered on the Commet's accident.

Cheers,

Okey, didn't know about that... Thanx =)