PERTH, Australia (AP) — Australia deployed Tuesday an airborne traffic controller over the Indian Ocean to prevent a mid-air collision among the many aircraft searching for the Malaysia Airlines jetliner that went missing over three weeks ago.
An air force E-7A Wedgetail equipped with advanced radar "is on its first operational" task in the search area in the middle of the Indian Ocean, the Australian Maritime Safety Authority said in a tweet. Earlier, Angus Houston, who heads the joint agency coordinating the multinational search effort, said the modified Boeing 737 will monitor the increasingly crowded skies over the remote search zone.
The three-week hunt for Flight 370 has turned up no sign of the Boeing 777, which vanished March 8 with 239 people on board bound for Beijing from Kuala Lumpur.
Malaysia has been criticized for its handling of the search, particularly its communications to the media and families of the passengers. In something likely to fuel those concerns, the government changed its account of the final voice transmission from the cockpit.
In a statement late Monday, it said the final words received by ground controllers at 1:19 a.m. on March 8 were "Good night Malaysian three-seven-zero." Earlier the government said the final words were "All right, good night."
The statement didn't explain the discrepancy or the significance of the slightly different sentences. The statement also said investigators were still trying to determine whether the pilot or co-pilot spoke the words.
At a news conference in Perth, Houston, the 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."
The search zone area has shifted as experts analyzed Flight 370's limited radar and satellite data, moving from the seas off Vietnam to the waters west of Malaysia and Indonesia, and then to several areas west of Australia. The current search zone is a remote 254,000 square kilometer (98,000 square mile) that is a roughly 2 ½-hour flight from Perth.
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.