Scientists: AC flt that plunged, injured 10, hit wave of air

[Widow]

Scientists says Air Canada flight that plunged, injuring 10, hit wave of air
By John Cotter (CP) – 7 hours ago

EDMONTON — Experts say an Air Canada jet that plunged more than 1,000 metres without warning last year, injuring 10 people, rose up and then dove down a massive invisible wall of smooth air called an internal wave.

The official cause of what happened to Flight AC-190 on Jan. 10, 2008, over a rugged area near the B.C.-Washington border is still under investigation by the Canadian Transportation Safety Board.

The internal wave transformed the routine flight from Victoria to Toronto into a terrifying roller-coaster ride that violently tossed passengers, crew and heavy drink carts around the cabin before the pilot made an emergency landing in Calgary.

Scientists not connected with the official investigation say the Airbus 319 hit an atmospheric phenomenon that can loom up out of nowhere and doesn't show up on weather or aircraft radar.

"This Air Canada plane was just unfortunate enough to encounter one of these waves," said Bruce Sutherland, a University of Alberta professor of earth and atmospheric sciences.

"This isn't something that occurs all the time. You are just really unlucky if you happen to capture a wave that has gotten to this large amplitude and has not yet broken. If a plane showed up behind them 10 minutes later, that wave would have overturned and broken and that plane would have encountered lots of turbulence, but they wouldn't have been carried up a thousand feet in seconds."

Internal waves occur in the atmosphere and the ocean. They're not unlike the disturbance caused when water flows over a rock. In the case of the atmosphere, wind blows over a mountain and creates a wave of air behind it that flows both up and down.

The size of the wave depends on how fast the air is flowing and on how much the air temperature changes with altitude.

"The wind is always blowing over the mountains. But every now and then it is just right to create these very large amplitude waves," Sutherland said. In some cases, such waves can be 20 kilometres wide.

Immediately following the Air Canada jet's troubles there were unconfirmed reports that the plane with 88 people aboard might have encountered "wake turbulence" - flying through the wake of a passing aircraft, perhaps a U.S. military stealth jet or a heavily loaded 747 cargo aircraft. There was also speculation about internal waves.

Canadian investigators at the time would only say there was a high probability the sudden plunge was caused by an external force.

Thomas Peacock, an expert on internal waves at the Massachusetts Institute of Technology, said he also believes the Air Canada jet hit an internal wave.

Peacock said he is working on a documentary on ocean and atmospheric internal waves for the Discovery Science Channel and hopes to interview the Air Canada pilots for the program that is to be broadcast next year.

"The Air Canada flight encountered a particularly strong internal wave which is why it had such a dramatic effect," he said. "It must have been a very strong event that took place there."

Radar helps aircraft avoid rough air currents. But an internal wave is a much smoother disturbance that can't be seen or detected in a cloudless sky, he said.

"These radar systems can detect the highly intense activity of turbulent air, but a nice smooth disturbance consistent with an internal wave cannot be picked up. But that disturbance has the dramatic effect that if a plane encounters it, it is swept up or swept downwards.

"You want to have your seatbelt on when that happens."

The Canadian Transportation Safety Board declined comment other than to say that a draft report into what happened to Flight AC-190 is being circulated to Air Canada and other organizations. The board's final report is expected to be released by March.

Air Canada officials also declined comment. The Air Canada Pilots Association did not respond to interview requests.

Sutherland said specific internal waves are difficult to predict without launching many weather balloons within an area, so the most effective way to deal with them is to ensure that flight crews are trained to respond quickly.

If a plane suddenly lifts without warning in areas prone to such internal waves, pilots may have only seconds or perhaps a minute or two to prepare for the plunge down the other side of the wave, he said.

"Even if they couldn't detect it in advance, they would see the signal of it when they hit one side of it and they could at least fix the problem before they hit the other side."

[SeptRepair]

Well there you go, I learned something new today.

[Pratt]

I presume they are talking about a mountain wave, or is there something else I don't know about?

[wxguy]

There are many other types of waves in the atmosphere other than mountain waves, like interfacial waves which travel between air layers of differing densities.

Or gravity waves....see below:

http://www-misr.jpl.nasa.gov/gallery/im ... -small.jpg

http://www.youtube.com/watch?v=yXnkzeCU3bE

Rossby Waves
http://en.wikipedia.org/wiki/Rossby_wave

Kelvin Waves
http://en.wikipedia.org/wiki/Kelvin_wave

Check out some of the math!
http://www.phys.ualberta.ca/~bsuther/co ... fluids.pdf

I don't think all of these waves would cause turbulence in an airplane, but they are interesting none the less!
It is all way over my head...

[Cat Driver]

I'm thinking the real problem here is pilots are not properly taught how to control the plunging movement and this training should be incorporated into the training manual.

[Campanola]

I presume they are talking about a mountain wave...

I guess so. Mountain waves are just a type of internal wave in the atmosphere.

"Internal waves are ubiquitous throughout the atmosphere. Strong generation regions in the stratosphere, such as mountain ranges, can generate a stream of internal waves propagating upward into the middle atmosphere. Internal waves may also be generated through convection, wind shear, adjustment of unbalanced flows near jet streams and frontal systems, and body forcing accompanying localized wave dissipation."

http://ams.confex.com/ams/pdfpapers/141085.pdf

I'm sure the TSB will be able to figure out what a mountain wave/internal wave is and will take all the possibilities in consideration.

[Four1oh]

Or just plain-old-crossing-the-jetstream associated turbulence....

[Liquid Charlie]

i don't know about how other people feel but when that old girl starts to surf and the trim starts to go in both directions I am always ready for that nasty surprise - wax those boards

[Pratt]

There are many other types of waves in the atmosphere other than mountain waves, like interfacial waves which travel between air layers of differing densities.

Or gravity waves....see below:

http://www-misr.jpl.nasa.gov/gallery/im ... -small.jpg

http://www.youtube.com/watch?v=yXnkzeCU3bE

Rossby Waves
http://en.wikipedia.org/wiki/Rossby_wave

Kelvin Waves
http://en.wikipedia.org/wiki/Kelvin_wave

Check out some of the math!
http://www.phys.ualberta.ca/~bsuther/co ... fluids.pdf

I don't think all of these waves would cause turbulence in an airplane, but they are interesting none the less!
It is all way over my head...

Very interesting stuff, thanks for the info, had not heard the term "internal wave" before.

[sanjuanview]

I was one of the Flight 190 passengers taken to hospital after the flight and I'm more than curious about what the TSB is going to say about this theory when they issue their report. It is a THEORY so far. From the morning after the flight, I read and saw nonsense being disseminated by reporters on what happened to us. I'm a lay person, but I doubt if scientists have access to the flight data from our flight...so it may enhance this interesting theory or disprove it. We'll see...

KB

[C-FABH]

It is a THEORY so far. From the morning after the flight, I read and saw nonsense being disseminated by reporters on what happened to us. I'm a lay person, but I doubt if scientists have access to the flight data from our flight...so it may enhance this interesting theory or disprove it. We'll see...

Thanks for your post, and I'm tempted to agree. If these 'science experts' are anything like the aviation experts I see in the media and television, well, I won't hold my breath...

[invertedattitude]

"US Stealth Plane"


I wish I lived in the minds of some of the people who write this stuff... well not lived, maybe take a short visit.

[wxguy]

Thanks for your post, and I'm tempted to agree. If these 'science experts' are anything like the aviation experts I see in the media and television, well, I won't hold my breath...

If Bruce Sutherland isn't considered an expert in his field, I don't think anyone is. I don't know how much he knows about aviation, but he sure knows what he is taking about when he is talking about waves in fluids.

[pdw]

OLD THREAD http://www.youtube.com/watch?v=yXnkzeCU3bE

I'd sent a private message to wxguy a year ago asking what ever became of the "internal wave" investigation. There was no response yet, so not expecting any.

Did the TSB investigation get to a conclusion ? If so, the safety databases don't have it yet ...

[GyvAir]

Investigation report:
http://www.bst-tsb.gc.ca/eng/rapports-r ... 8w0007.asp

Wake turbulence generated by the 747-400 they were following gets the blame.

[pdw]

We can begin to see why that might have been confused with some kind of other wave(s) at first.

The accident aircraft climbed thru this path of lingering wake (something like large waves) in complying to the ATC clearance, to the same altitude of the 747 travelling at 490kts eastbound about 10.7nm ahead of them (new about it at 4nm and cleared after 8nm); when cleared they did not know anymore about the 747 or its location nor would their controllers have known they'd be sending them into encountering its wake there ... seeing the airbus was trailing already at more than twice the mandatory separation distance from the origin of the 747's vortices. Looks like the 747 had just passed them a bit earlier off to the right and at the 2000ft higher altitude (from the large track-diagram in the report).

They closed in on the wake of the 747's 81degM heading while in stable air (where wake can sometimes exist longer) on their gradual 3 degree converging heading of 78degM (see "expanded area") while also climbing towards it from below off their previous flight level from 1600ft lower at FL35. (Perhaps an error check is required here since on the track map in the report it looks like the accident aircraft is on the more southerly heading.)

The 747 wake turbulence was first intercepted starting at FL36.6. When using the accident aircraft's "450kt" cruise speed location on the trailing end of the 10.7NM separation distance in the findings, it's true in that way at it's own speed was "84 seconds" behind the actual wake-making point of the 747 at the first moment of encounter. But is also correct to say (a report error check required here) that the passing/faster 747's speed is what counts here for the wake's age-determination for the airbus, not the slower airbus's speed. That way the wake was only 78-79 seconds old. Yet even if another 6-7 seconds less spacing-time between them, the minimum time-separation there should have been 120-180 seconds according to the safe wake-following time/distance chart provided in the report.

So the crew were not aware it was a wake encounter, being simply cleared there by ATC, and originally had considered their control disaster a flight computer malfunction as recorded in their emergency transmission.