Analysis: Pessimism Grows as Search for Missing MH370 Drags On

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PERTH, Australia - The signs aren't good. The search coordinators aren't optimistic. And the chief of the new group heading the search for missing Flight MH370 is warning that the days of intensive searching might be numbered.

"Inevitably, if we don't find any wreckage on the surface we are eventually going to have to, probably in consultation with everybody who has a stake in this, review what to do next," retired Air Chief Marshal Angus Houston said.

That day may come soon.

The new search zone is yielding no results after more than 500 hours of searching by dozens of aircraft.

The Australians have been doing a lot to dampen down expectations of a breakthrough. Australian Prime Minister Tony Abbott has said several times in the last week that the search effort is "extraordinarily difficult."

The Australian Maritime Safety Authority has stopped giving details of objects found in the sea, preferring to say simply "nothing significant found" at the end of a day's searching.

The area being searched remains enormous. On Tuesday, 10 ships and 12 planes scoured the Indian Ocean; more than 100 men and women in the air and more than 1,000 at sea.

Still, no one has the slightest idea where the Malaysia Airlines jet hit the sea.

Among the vessels joining the search in the coming days is the Australian naval ship Ocean Shield, which has been fitted with a sophisticated U.S. black box locator and an underwater drone.

It left on Monday but will take "several days" to reach the zone. Time is not on its side because the signal transmitted by the missing aircraft's black box will fade and die about 30 days after a crash because of limited battery life, leaving investigators with silence from the plane and a much more difficult task of finding it.

Meanwhile, search coordinators are worried about the possibility of a mid-air collision between planes flying low and fast outside normal air traffic control. So Australia will deploy a modified Boeing 737 to act as a flying air traffic controller to prevent such an incident.

One U.S. search plane, a P-8 Poseidon, has flown just 200 feet above the water for long periods, while an Australian P-3 Orion flew briefly at 100 feet above the ocean.

It is an intensive search, to be sure. And no one doubts the high morale and the high hopes of the air crews.

But back at search headquarters, their leaders are growing more cautious and less confident by the day.