WASHINGTON, Dec 31 — Nearly 12 years after Malaysia Airlines flight MH370 vanished with 239 people on board, the search for answers to one of aviation’s most haunting riddles resumed Tuesday in the remote southern Indian Ocean.

Armed with cutting-edge deep-sea robots and smarter data, US investigators are scouring the seabed for clues that have eluded governments, experts and grieving families for more than a decade.