Thursday, 8 February 2007

Turbulent Townsville

Sometimes, the weather just doesn't work in your favour. Whether its raining out weekend sport or a BBQ, bringing an early end to the snow season, or simply melting the polar caps, raising sea levels and displacing millions of people, it can often be a minor inconvenience.

But on other occassions, it can be truly annoying.

I am currently sitting in the airport lounge in Townsville, North Queensland, awaiting my extremely delayed flight and hoping beyond hope that I don't have to stay here any longer. Townsville is a town that is built around James Cook University, the Army and the North Queensland Cowboys Rugby League team. However, univerisity hasn't gone back, much of the Australian Army is deployed overseas, and its not rugby league season yet, so suffice to say, there is not alot to do. Although, I'm not sure whether I would be tempted by that combination of attractions in any case...

No, to be fair, Townsville has its fair sure of beautiful attractions and lovely people. I'm just grumpy - that grumpiness that only airports can bring out of you!

Northern Australia is currently in the grip of cyclonic weather conditions. Cyclone Nelson has cut off much of the north by road, and caused massive flooding. This is a very strange thing to see coming from Sydney, which like much of the rest of the country, is drought-striken and in a water crisis.

So for my flight to be delayed is not surprising. However, for my flight to be delayed because the plane is late from Sydney because of Sydney storms, whilst it is perfectly clear outside here in Townsville, is rather infuriating! (Marc - I'm adding this 6 hours after we were supposed to leave, and we're still here. Each hour they delay the departure time by an hour.)

OK, time to stop complaining, and make something sciencey out of all this. One of the "features" of the trip up, and considering the weather conditions probably the trip back, was turbulence. Turbulence is air movement that cannot normally be seen and whilst many people enjoy this aspect of flying, I struggle with it!

There are a number of ways that turbulence can come about:

Thermals - Air rises when it is heated by the sun, and cold air sinks. So if one mass of air heats up, this can cause air flow causing turbulence.

Jet streams - At high altitudes, there are fast air currents. These can shift, causing a disturbance in the nearby air.

Mountains - Air passes over mountains and causes turbulence as it flows above the air on the other side.

Wake turbulence - If you are flying near the ground, a passing plane or helicopter can set up small, chaotic air currents.

Microbursts - A storm can cause a strong downdraft close to the ground.

The danger with turbulence is that it cannot always be predicted. The cockpit suffers least from turbulence, whilst the rear of the plane cops most of the disturbance. You don't need clouds for turbulence, however I usually notice it most when flying through them. On the way up, the pilot tried to stay below the clouds that were causing the turbulence. However, after a period of time, the clouds got lower and lower, and the plane couldn't continue to stay below them. However, the pilot said we were too heavy to fly above them - so we flew in the clouds for the best part of the flight, and it was a bumpy ride!

Aircraft radars can't detect turbulence. Turbulence is the leading cause of in-flight injuries, so remember to keep those seat-belts done up! It can range from very mild, to the extremely dangerous (but rather unlikely) case of the plane being totally out of control with massive changes in altitude. Between 1981 and 1997, there were 342 reports of turbulence affecting major air carriers. Three passengers died, two of which were because they were not wearing seat belts. 80 suffered serious injuries, 73 of these were also not wearing their seat belts.

One example of turbulence was a flight from Singapore to Sydney with 236 passengers on board, as well as and 16 crew. The airplane encountered turbulence over central Australia when it hit an air pocket and dropped 100 m. Nine passengers, including one pregnant woman, and three crew members suffered neck, back and hip injuries, with one of the passengers requiring surgery. They were all not wearing seat belts.

I'll get this out on the podcast soon, assuming I get back..... (mp3 here)

For more info and some examples of turbulence incidents, see: Civil Aviation Safety Authority
For a fluid dynamics explanation, see here.

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