NTSB Briefing, NTSB claiming .3 to .8 g wake encounter caused crash?!?!?!

CNN | 11/15/2001 | me

[The Magical Mischief Tour]

This is Bull $h!t!!!

The NTSB is LYING like rugs!!!

NTSB dude just claimed that .3 to .8 g's encountered during the wake encounter caused the Airbus to break up in flight...

Even a male reported asked "is this even possible".

"Isn't this normal bumping encountered when flying?"

Even the media don't believe them!!!!!

[samuel_adams_us]

Some of those whimps should be given an all expenses paid tour of the beachs of Normandy so they walk among those who gave them right to be whimps.

[Dan Day]

FINALLY! The sabotage advocates seem to think the American public will be more likely to fly knowing that the tails of commercial airliners just fall off every once in a while. Phew! What a relief! Whomever the spook was who came up with this ingenious cover story needs to be promoted to the front of the short bus immediately. You conspiracy advocates need to be a little more creative.

Thank you.

I've been amused at the apparent self-contradiction:

Conspiracy fan: "The government is cleverly conspiring to hide The Truth about terrorism, so as to maintain the public's confidence in the airlines!"

Skeptic: "Um, it seems to me that telling people that planes just fall apart during normal would scare *more* people, not fewer."

Conspiracy fan: "The government is stupid, what can I say?"

I don't think it's the *government* that isn't being too bright here...

[Solson]

Yes, that would be part of it. The other part is the design. an aircraft engine attachment is designed to withstand certain loads in certain conditions. If severe vibration occurs, these pylons are not designed to withstand that sort of force. Morover, couple that with loads coming from other places and these engines, probably any engine would detach.

It's like an I-beam. It's designed to withstand a large load bearing in a certain position. However, stand it on end and it will fail under a much less load factor.

[justlurking]

No commercial plane that I know of can sustain more than about 2 g's in a yaw-only induced turn without having problems. Think about it - twice the plane's weight applied only to its vertical tail surface.

I think I see your point, and here's where the measurements are going to make it difficult. I don't know exactly how they measured the .3g, but I'm guessing that they recorded them from accelerometers in the planes INS (presuming that it had one).

But, it measures only the acceleration of the entire plane, not just the rudder... although the placement of the accelerometer might be a contributing factor. We don't know where that force was applied on the plane -- simply that the whole thing was "bumped" at a certain rate. We don't know how concentrated the push might have been. Given that AA 587 was 2 minutes behind the JAL flight, any wake vortex should have had plenty of time to dissipate into the surrounding air.

However, I keep coming back to the concept of "manevering speed". The plane is supposed to be able to withstand full deflection loads on the control surfaces at and below that speed. The lift and control surfaces are supposed to "stall" and become ineffective before breaking under turbulence. How could such a light loading cause a catastrophic failure, while going unnoticed for so long?

[caa26]

I agree. Just go to LAX its a constant parade of airplanes taking off and landing all day long. It appears that pre-exsisting structual damage and/or pilot error combined with wake turbulence could have caused this catostrophy.

[Solson]

EXACTLY! And the Airbus A300 was the FIRST commercial aircraft using a significant amount of composite materials in its construction. They started with the rudder, then the vertical stabilizer, then all over parts of the aircraft. These materials were fatigued(a technical term for those looking to flame) and undetected. The turbulence caused the failure.

[justlurking]

No, half the speed would be 1/4 the accel, or .175 g.

Ooops. It's been a long time since I did this stuff. That's why I asked.

Thanks for keeping me honest.

[samuel_adams_us]

Time to outlaw the Airbus 300 and make it mandatory to use metal parts, if composite parts are failing that is.

[Starrgaizr]

I floated out of my seat (since then, I always wear my seat belt), and came down real hard. I'd guess the uplift impact imposed thee G's on the aircraft.

Floating up implies zero or slightly negative load factor. If there were -3Gs you might not be posting today.

[Blueflag]

OK OK

I am not being accelerated while lying in bed. HOWEVER!!! I do experience a constant force that would accelerate me at 32 ft/sec2. So in that context, I feel the force of 1 G while lying in bed. Adding .3 more to that would be trivial, like having my middle son jump on me in bed.

;-)

later guys, gotta go fly from LGA to ATL (on DELTA with BOEING aircraft. only thing better would be Lockheed)

[ginoson]

.3 to .8 g's is NOTHING! I would expect that forces of .3g's are experienced on most flights. If you've ever hit rough turbulence you've experienced .8g's. Tactical fighters rountinely pull several g's.

You'd better believe they can take more g's. I went through AF pilot training back in the 60's in T-37's & T-33's. After indoctrination flights at the beginning, my instructor & I were up on a spin demonstration flight. He did the first one complete with recovery & then instructed me to do one. Everything was fine until, during recovery, when I popped the stick forward, neither he nor I knew that I had hit the trim button on top of the stick & trimmed the airplane full nose down. In this mode the airplane would not stop it's descent, even with the stick full aft. When my instructor saw that I was not able to pull it out, he took control, & tried first an outside loop which pulled 3.5 negative G's, & then he finally figured that it was the trim. He then honked it back & we pulled 7.5 positive G's. This all started at 21,000 ft. & recovery was complete at 8,000. As we limped back to base, with crap in our pants, he stated that as we went through 10,000 ft. he was just before telling me to hit the silk, when he discovered the trim problem. The airplane wasn't damaged at all. Just our nerves. These airplanes can take the g forces.

[samuel_adams_us]

Would that better include the new fighter jet contract?

[michigander]

National Transportation Safety Board Chair Marion C. Blakey, and lead investigator George
Black Jr. addressed the press with information concerning the investigation of American
Airlines Flight 587, at the JFK Holiday Inn, in the Jamaica section of the Queens borough of
New York, Nov. 14, 2001. This is one of two charts used in the presentation. (AP Photo/Robert Spencer)

---

According to this image of the (supposed) radar tracks of both planes, flight 587 maintained a steady northerly .5 NM separation (sufficient?) along a parallel flight path.
This "wake turbulance" appears (to a know nothing like myself) to be a localized event along a flight path (although it's likely that it moves laterally depending on the prevailing winds and also, I've read that it has a tendency to "sink").
It would seem that in this case the less the interval between the aircraft the less likely the scenario becomes.

[jlogajan]

NTSB claiming .3 to .8 g wake encounter caused crash

No, they're saying the plane encounter wake turbulance of that magnitude. It is a potential cofactor. Please unwrap the tinfoil around your heads, people.

[Melinator]

If you weigh 200 lbs and were in the airliner and got a .8 side gust it would shove you into the side of your seat with a force of 160 lbs. That would get your attention!

According to the NTSB, it would do a lot more than that! I suspect your seat would rip loose from its floor bolts and punch right through the side of the aircraft as if it were made from tinfoil. Not only that but punching through the side of the aircraft like that is dangerous, particluarly if your seat also happens to puncture and rip the fuel-laden wings from the craft. That and a few good electrical shorts from where you take out a wiring bundle as you pass through the hull would make it look like an explosion and flames to persons observing from the ground, when it really is just a freak series of once in a lifetime events. Case closed.

[Centurion2000]

It's called total B$ ....

[Mr. Jeeves]

It's looking pretty weak. I still can't figure how a 747 wingtip votice creates a .8g force, anyway. Knocking a Cessna out of the sky is one thing, but the A300 stabilizer must have been terribly weakened beforehand.

[Dan Day]

The only way that wake turbulence would be able to cause the rudder to get a g force sideways would be wind force.

Air turbulence *is* wind.

If you had a 2g force from the left, for example, that air pressure would move the tail to the left. This should cause the airplane tail to move to the right.

Moving the tail to the left causes the tail to move to the right? Um, could you run that one past us again?

If it moved to the right then the right side of the airplane will also build up air pressure, which leaves a 2g force, but much lessened by the almost identical pressure on both sides.

"Both sides" of *what*?

So g force isn't really applicable to anything in this case.

Thank you, Mr. Wizard... Come back when you've sobered up.

If the plane fell sideways(one wing up 90 degrees), you would have no g force, but would probably lose the rudder.

Yes, a plane in free fall would have "no g force". So what? And how would that make it "lose the rudder"? It wouldn't.

So NTSB is playing games, in my opinion

Could you be any less coherent?

Look, a sideways gust of wind on the plane would produce G forces. Period. And no amount of handwaving changes that.

PHYSICS LESSON

Let's boil this down to actual math. A 0.8g lateral acceleration on the plane means the amount of force on the tail was sufficient to swing the plane's rear 51.2 feet in two seconds, starting with no rotation at all. Imagine how hard you'd have to push on the tail to get it moving fast enough so that it has travelled 51.2 feet within two seconds of you starting to shove on it.

Planes are heavy. They don't like to change position that fast. That's a lot of force, and a lot of stress, in a direction that the tail was not designed to withstand very much of.