AirAsia flight QZ8501: A tale of two search sites

The expanded search area for the ill-fated AirAsia plane.As the search area expanded for missing AirAsia flight QZ8501, comparisons were made with the missing Malaysia Airlines flight MH370 and even flight MH17, which was shot down over Ukraine in July.

On Tuesday morning new maps were issued showing the expansion of the search area to 156,000 square kilometres.

Thirty ships and 15 aircraft, including helicopters, were reportedly searching the area and all leads, including those from local fisherman, were being followed up.

Comparatively, when the Australian Maritime Safety Authority took over the search for MH370 in the Indian Ocean, a search area of 600,000 square kilometres was established, an area the size of France.

Now, almost 10 months since the ill-fated MH370 disappeared from air traffic control radars, there has been keen interest in comparing the search sites and practices in the aviation disasters.

“I think it’s nowhere near as problematic as MH370, so it’s not likely to take as long,” said Dr Geoff Dell, Discipline Leader in Accident Investigation at Central Queensland University.

“Though it’s still a really big search area and, because of the limited range of the beacon, that means the search grids that you run have got to be fairly tight and close together.”

When the search area was increased to 156,000 square kilometres on Tuesday, the number of search sectors in the grid also increased from six to 13.

The depth of water in the Java Sea over which QZ8501 went missing is about 40 to 50 metres – a stark difference to the depths of more than 4000 metres confronted by crews searching for MH370.

Such depths affect the ability to accurately determine the direction of the signal from an aircraft’s black box.

“You’ve got to have some sort of hydrophone [a type of underwater microphone] that allows you to differentiate signal strengths,” Dr Dell said. “The one they towed around for MH370 was a kind of wedge shape with hydrophones on each side and the computer could look at different signal strengths from one side to the other.”

In the case of flight QZ8501, Dr Dell said there was not much conjecture about the location of the aircraft, which meant there was perhaps greater confidence in the search.

“One of the differences with this flight and MH370 is the crew clearly asked for an amended clearance to get around the weather, and were granted to deviate off track. What is probably not known is just where they deviated to.”

If the aircraft flew into a thunderstorm cell at about 30,000 feet and suffered a structural failure, Dr Dell said that “a bit like with MH17, debris is going to be spread over a fairly large area”.

“Rule No. 1 in aviation is you don’t fly through the middle of thunderstorm cells because there is a lot of energy and turbulence and fairly significant wind shears,” he said.

In storm cells with  updrafts of about 160 km/h hour, smaller aeroplanes have been known to fly in at about 5000 feet and be spat out at the top at 40,000 feet.

“Airliners are stronger than that but still there are limits to their structural capabilities,” said Dr Dell.

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