the malaysian airliner mystery now crosses the four-week mark with a new question about the pilot s flight simulater. on the water, two vessels are using special sonar technology to try to detect pings from the jet liner s flight recorders before their battery runs out. one of the ships is using an underwater microphone from the u.s. navy. up to 13 planes are part of today s operation conducting a visual search for remnants of the missing jet. no trace has been found four weeks after it took off from kuala lumpur for beijing. nick raja is live with the investigation, and erin is live in perth. erin, let s start with you.