Australia says search for MH370 can 'drag on'

Some of the aircraft have been dropping as low as 200 feet (60 meters) above the water—and occasionally dipping even lower for brief periods—raising concerns of collisions with ships that are crisscrossing the zone.

Under normal circumstances, ground-based air traffic controllers use radar and other equipment to keep track of all aircraft in their area of reach, and act as traffic policemen to keep planes at different altitudes and distances from each other.

This enforced separation—vertical and horizontal—prevents mid-air collision. But the planes searching for Flight 370 are operating over a remote patch of ocean that is hundreds of kilometers (miles) from any air traffic controller.

The arrival of the E-7A “will assist us with de-conflicting the airspace in the search area,” Houston told reporters in Perth.

The plane can maintain surveillance over a surface area of 400,000 square kilometers (156,000 square miles) at any given time, according to the air force's website.

Houston, a former Australian defense chief, called the search effort the most challenging one he has ever seen. The starting point for any search is the last known position of the vehicle or aircraft, he said.

“In this particular case, the last known position was a long, long way from where the aircraft appears to have gone,” he said. “It's very complex, it's very demanding.”

“What we really need now is to find debris, wreckage from the aircraft,” he said. “This could drag on for a long time.”

Malaysia has been criticized for its handling of the search, particularly its communications to the media and families of the passengers. In its latest misstep, the government on Monday changed its account of the final voice transmission from the cockpit.