Japan Airlines 747 and American Airlines A300 Flew Parallel Trajectories, 1 Minute 30 Seconds apart

Megadata Corporation (Via PRNewswire ^ | 11/15/01

[Fixit]

For Information purposes only...

[Dirk McQuickly]

if I'm reading this correctly, 587 could not have been in the wake of the 747? Clarify?

[SGCOS]

Trajectories
* JAL 47 and AAL 587 flew parallel trajectories, which were .75 miles apart
* JAL 47 flew at a higher altitude than AAL 587 -- ranging from 400 feet to 1000 feet higher

Can the turbulence wake move .75 miles in 2 minutes while dropping 400 - 1000 feet?

[NC_Libertarian]

Wake turbulence does descend I beleive.

[Blueflag]

Dirk-- Picture in your mind the wake of a boat. The farther behind the boat, the wider the wake is. Same for wing vortices. They also tend to sink, and the wind was blowing towards the SE. All of this would indicate it is possible that 587 could encounter the wake of the JAL FLT 47.

Having stated that, let me state I do not understand how wake turbulence could cause an A300 to disassemble itself in the air.

[justlurking]

if I'm reading this correctly, 587 could not have been in the wake of the 747?

Maybe. Wake vortices tend to sink down and out. But, they are affected by prevailing winds, too.

It would take a more sophisticated computer model than I could do in a reasonable amount of time. I hope that someone is doing so, though.

[VRWC_minion]

Can the turbulence wake move .75 miles in 2 minutes while dropping 400 - 1000 feet?

The wake will drop and drift with prevailing winds.

[Fixit]

Big vortices to little vortices, they give their velocity,
To smaller vortices and smaller vortices, unto viscosity.

~~ Bizarre poem my fluid goddamnits dynamics professor taught us.

As far as wakes dropping, I'm not sure if they drop so much as they tend to spread out. Of course, as they spread out they lose speed and intensity, eventually becoming heat in the air.

[Fixit]

That I can not answer.

[SteamshipTime]

As someone with a remote connection to aviation, and from what I've read, it probably can. However, I would not expect the effects on such a large plane to be so discrete. I would expect a general loss of control rather than the vertical stab and rudder falling off and then two engines. If the goal is to assuage people that there was no sabotage, one would think they'd be releasing photos & analysis of the shear points ASAP. Of course, I have no expertise in these matters.

[eno_]

Yes, it can move that far, and drop that far, in that amount of time. But it is still a very far reach that wake turbulence, or clear-air turbulence, or any kind of wind on what was a clear, calm day, could rip apart an AB300. This appears to make it clear it was not a mid-air near-miss or anything so unusual that it might become plausible that the forces on the plane were so great as to tear it apart. It also does not explain the bright flash and loud bang witnessed by observers on the ground. Nor does it explain the engines falling off. I am not sure what does explain all this.

[SGCOS]

If the vortices can travel with prevailing winds, a piece of info not included was whether AA 587 was upwind or downwind of JAL 47.

The video taken from a few miles away of the crash site indicated a pretty hefty, steady breeze. (Making the assumption that the prevailing winds did not change within minutes after the crash.)

[SGCOS]

And while I'm thinking of it, in the video shot of the AA 587 engine sitting in the gas station parking lot, there is a fireman kneeling on the side of the engine.

At the beginning of that clip, a man walks over to the engine and takes something out. Whassup with that?

[eno_]

A mile and a half is a long way compared with, say 20 feet, which is how far away the Chinese fighter was off the wing of our electronic surveillance plane when it got sucked into turbulence, got out of control, had a midair collision and crashed. The surveillance plane, despite having its nose taken off, a bent propeller, etc. made it to a landing. Gotta believe running into a plane is worse than running into a plane's wake.

[Reeses]

Another point: if the 747's track was higher than the A300's, it was probably climbing faster and flying slower. Combine that with the extreme weight and heavy wing loading of a 747 you get powerful vortices. I remember a case in S.Calif. where a Lear Jet was flipped fully upside down during landing from a vortex and crashed. If a vortex could flip a multi-ton plane, it probably has sufficient force to snap off a weakened tail fin on an A300.

[Blueflag]

Reported surface winds were 11 Kts towards the SE.

[Fixit]

Bump for archive

[justlurking]

Reported surface winds were 11 Kts towards the SE.

As someone else noted, I didn't see anything about how the tracks paralleled -- i.e. whether AA 587 was upwind or downwind.

But, I will also note that winds aloft are often different than surface winds. It looks like AA 587 got as least as high as 2800 feet, and the FAA will have wind aloft forecasts for 3000 feet.

Presuming the data from the blackbox is recovered, they should be able to calculate an estimate by correlating the airspeed and heading data with the ground speed and ground track data from the radar.

[jlogajan]

Wake vortices tend to sink down and out. But, they are affected by prevailing winds, too.

Actually, they ARE the wind -- so to speak. That is, wake turbulence is a local disturbance in the mass of air that is moving with respect to the ground and gives rise to the concept of wind.

In addition, to keep a plane up, air has to move downward. Of course, this creates a low pressure above, which then sucks in air, hence you get a circulating flow -- but it must drift downward until it is supported by the surface of the earth, which of course is non-fluid.

But yeah, downward, outward, and carried with the wind.

[discostu]

But the Chinese fighter was next to our plane thus ahead of the turbulence. Clearly under normal circumstances turbulence doesn't tear planes apart, unless there's something wrong with the plane to start with, then it could be the final stressor.