Ships from six navies, dozens of military aircraft, sweeps with radar technology that can spot a soccer ball from hundreds of feet in the air - all have failed to find a single confirmed trace of a Malaysia Airlines plane that vanished three days ago. For the sailors and aircrew, it has been a frustrating operation. One reported sighting of the plane's tail turned out to be a few logs tied together. On Monday, a Vietnamese jet spotted what it believed was a yellow airline life raft floating in the sea. A helicopter scrambled to investigate pulled a moss-covered cable reel cover from the sea. The massive search is mainly in a 50-nautical mile radius from the point of last radar contact with the plane, midway between Malaysia's east coast and the southern tip of Vietnam.