Southwest 737-300 Emergency Landing After Fuselage Tears Open

[MCM]

G'day Gabriel and Evan,

Gabriel, you were half right.

The spoilers do need to be extended manually.

However:

FLCH will retard the thrust levers for you. The role of the mode (certainly on the 767, 747 and 777 at least) is to, as the name suggests, change level, and thats what it does. It will use any thrust between idle and climb thrust.

If you set an altitude other than existing, the aircraft will try to effect that change within roughly 2 minutes if it can - if not, it does the best it can. So, for a change of more than a couple of thousand feet down, it will reduce the thrust to idle while pitching for the speed set in the MCP.

You now change the MCP speed to 270kts. The plane will climb!!! (even when you set an altitude below the current one) because it must do so to reduce the speed from the current 300kts to the set 270.

It will reduce the rate of descent to decelerate, but because it has automatically changed the thrust to idle it won't need to climb.

What you say is correct if you do not have the autothrottle engaged - you would need to manually close them to have any effect.

[Gabriel]

Hello Mr Gabriel. A very interesting concept. I don't understand how to keep 1 G , or indeed any other G. Is there a dial to show it, a G meter?

To begin with, it never minds really because this maneuver is not what is done, as I found out in this thread.

Now, going to the technical aspects.

No airplane that I have flown (a couple of small piston singles) had a G indicator, and as far as I know your typical airliner doesn't have one either, at least easily available to the pilot.

That said, 1G is what you feel when you are just sitting in your armchair. If you are at more ore less than 1G, you feel it. If you fell lighter than usual (maybe associated with "butterflies in you belly") you are at less than 1G. If things drop up you are at less than 0G. If you try to reach a knob and feel that your arm weights more than usual you are at more than 1G. We are pretty sensible to the Gs, especially those below 1G.

I just cant get a mental picture. You roll 30' and where does the G come from?

The Gs is the "load factor". It's the lift/weight ratio. While at cruise, you were flying at 1G. During this maneuver, you just keep the same 1G. The G doesn't "come" from anywhere.

Are you turning the aircraft with the rudder? Or does the aircraft turn towards the direction of bank without rudder?

You do it just as usual. You roll with the ailerons and use the rudder to keep the plane in coordinated flight. The difference is that, unlike a normal turn, you don't pull up to keep the nose from going down and the altitude from dropping because, alas, you want to loose latitude. In a normal turn where you want to keep the altitude you pull up, thus putting the plane at more than 1G.

OK, put the brakes up to reduce speed and max allowable is reached, but what if we're still not below breathing altitude?

While you keep the airplane turning but keep it at 1G, the sink rate will keep ever increasing. When you achieve the desired speed you roll back to wings level still keeping 1G. Then the plane will not increase the sink rate anymore but the plane will still descend at the sink rate you had achieved.

[Gabriel]

Gabriel, you were half right.

And half wrong. Ok, it was a risk Iw as willing to accept.
What I'd said was based in my, eerrrr... knowledge ... of the MD-80 autopilot.

[guamainiac]

No Gabe, 1 G is what I feel if I push my dead stock Corvette into a turn.

Specifically, with Goodyear Eagle GT (wide "square" and big), if I sling into a turn just after it breaks it will have developed a G. A very good car will do usually .08 and a ZR Corvette (close to an RS1 Porsche), will do perhaps 1.4.

Those a side forces but if you translate them that is still pretty powerful. Don't try to hold a cup of coffee during changes in direction.

I don't get how this becomes so neutral in your chair scenario. Sitting static has an inherent down force but these all involve changes in direction.

This is why they put grab handles in cars.

[Gabriel]

No Gabe, 1 G is what I feel if I push my dead stock Corvette into a turn.

Specifically, with Goodyear Eagle GT (wide "square" and big), if I sling into a turn just after it breaks it will have developed a G. A very good car will do usually .08 and a ZR Corvette (close to an RS1 Porsche), will do perhaps 1.4.

Those a side forces but if you translate them that is still pretty powerful. Don't try to hold a cup of coffee during changes in direction.

I don't get how this becomes so neutral in your chair scenario. Sitting static has an inherent down force but these all involve changes in direction.

This is why they put grab handles in cars.

If the wheels make a side force equal to one time the weight of your car, you are at 1G laterally.

If the wheels make a forward (or back) force equal to one time the weight of your car, you are either accelerating or braking at 1G longitudinally.

If the wheels make an upwards force equal to one time the wight of your car, you are at X G vertically.

Please solve X and tell me if that value of X would apply with you in your car comfortably parked at the Wal-Mart parking lot, or in your armchair for the matter.

[Highkeas]

From today's AIAA newsletter:

Possible Manufacturing Defect Considered In Probe Of Southwest's Fuselage Rupture.

ABC World News (4/22, story 2, 2:10, Sawyer) questions prior thinking that linked the fuselage rupture on board Southwest's Boeing 737 to metal fatigue because part of the problem may go back to the assembly line. Investigators "are focused on rivets, thousands of metal pins that hold the pieces of an airplane together. The concern is that, in the area that failed, those pieces were not held together as they should have been. At this seam in the fuselage, where one piece of metal overlapped another, sources say some of the rivet hopes were not sized correctly, that the two pieces were not fastened together tight enough at the seam."
The Wall Street Journal (4/25, Pasztor, Sanders, Subscription Publication) notes all of the 737s that were found to have cracks in the skin were built in Wichita and close enough in time to make investigators wonder whether it was a production problem with a few workers.

I suppose "hopes" should read "holes."

[guamainiac]

With the rivet being of a more dense material than the skin would the expansion and contraction of both materials alter the size of the holes over time?

[Highkeas]

With the rivet being of a more dense material than the skin would the expansion and contraction of both materials alter the size of the holes over time?

The rivets and skin would both be the same density (assuming alum alloy rivets are used). Two problem areas I have encountered in the past are:
(1) The countersink is too deep leaving a knife edge on the inner surface of the skin, or
(2) If the two skins were drilled at the same time, debris can get caught between the skins. This results in a bending load being applied at the skin/rivet interface.

[guamainiac]

Would there be any traces of, and this is probably technically wrong but, something like smoking or staining, I guess dust or oxide?

To align holes over that large a surface it almost has to be done at the same time (the problem for me is a 1960's mind trying to visualize 2010 technology).

[guamainiac]

When these parts were manufactured it had to be in huge jig or something?

Would that have been an automated process? I almost want to believe that there had to be a specific bit used and it was not an individual mechanic or fabricator. Could it be even something as simple as a dull bit, insufficient lubricant or similar problem that caused to much heat or weakening?

thanks highkeas ..

[Highkeas]

Here is yesterday's preliminary NTSB report (including some photographs of the damage):

http://www.ntsb.gov/Pressrel/2011/110425.html

[Highkeas]

From today's AIAA newsletter:

Poor Workmanship Cited In NTSB Report On 2011 Tear In 737’s Roof.

The AP (9/29, Johnson) reports the NTSB’s report on the 2011 in-flight tear in the roof of a Southwest Airlines 737 jet indicated that when the plane was assembled, “two panels appeared to have been misaligned, and many rivet holes were drilled incorrectly.” The NTSB is quoted as stating that this showed “a lack of attention to detail and extremely poor manufacturing technique.” According to the article, the NTSB said that “hidden cracks” started forming “from the rivet holes soon after the plane entered service and had been growing slowly ever since.”

I found the NTSB report

http://www.ntsb.gov/doclib/reports/2013/AAB1302.pdf