Saturday, exactly four weeks after the MH370 vanished with 239 people aboard, 13 military and civilian planes and nine ships were racing against time to locate the plane and most urgently its flight recorders before their batteries run out. They were joined by the Australian navy’s Ocean Shield and British HMS Echo which carry sophisticated underwater equipment. Search experts warned that this equipment moves slowly over small areas. Scouring hundreds of thousands of square miles of Indian Ocean will be a long business. No sign of the missing Boeing 777 has been sighted so far.