The Bluefin-21 is diving within a 10-kilometre (6-mile) radius of an area where signals were detected on April 8 that may have been emitted by one of Flight 370’s black boxes, said the Joint Agency Coordination Centre, the Australian agency set up to oversee the operation from Perth. The submarine will start its ninth mission later today and as many as 10 planes and 11 ships will comb 49,491 square kilometres of ocean for debris, it said by e-mail.

At 45 days, the hunt for the Malaysian Airline System Bhd. jet, which disappeared March 8 with 239 people on board, is the longest for a missing passenger plane in modern aviation history. The Bluefin-21’s side-scan sonar, which bounces sound waves off the ocean floor to create images of the seabed, is pivotal to the search for wreckage because the batteries in the aircraft’s black boxes have probably expired.

No signals have been detected since four audio pulses, which may have come from the crash-proof recorders, were detected from April 5 to April 8. — Bloomberg