Thursday marks the fourth year since Malaysia Airlines Flight MH370 went missing with 239 people on board while traveling from Kuala Lumpur to Beijing. The plane lost contact with air traffic controllers March 8, 2014, and is believed to have crashed in a remote part of the southern Indian Ocean.

Malaysia, China and Australia launched a massive search operation to locate the plane. The search for missing Flight MH370 became the costliest operation in aviation history. However, the tripartite decided to call off the search in an area of 46,332 square miles last year after finding no concrete clues as to the whereabouts of the jet.

In January, Malaysia agreed to pay United States’ firm Ocean Infinity up to $70 million if it found the plane during a search effort that is underway and expected to end in June. In its first statement since beginning the search, Ocean Infinity expressed optimism in finding the missing plane. 

“We have gone through a number of rough days,” two Malaysian navy officers aboard the search ship, Azmi Rosedee and Adbul Halim Ahmad Nordin, told the New Straits Times. “Operations continue even when the sea is rough … but it makes it difficult for us to deploy and recover the AUVs [search vehicles]. This slows us down.

“Aside from that, the seabed of the search areas is hilly and uneven. This also disrupts the AUV’s capability to thoroughly sweep the areas.”

Texas-based Ocean Infinity — which signed a "no cure, no fee" deal with the Malaysian government to find the jetliner — has scoured 6,177 square miles of the 9,652 square miles priority area in a remote part of the southern Indian Ocean, where the ill-fated plane is believed to have gone down.

A full investigation report into MH370’s disappearance was set to release on the fourth anniversary but was suspended pending the outcome of the new search. Malaysian investigators said any new evidence uncovered is “likely to significantly affect the investigation.” 

“In the event that the aircraft is found, the team will conduct further investigation,” investigators said in their annual interim statement sent to families of those aboard the plane. "If the aircraft is not found and a decision is made to discontinue the search, the team will resume the completion of the report and release it in the months ahead.”

Here's what we know so far about Flight MH370 and the ongoing search.

  • The Boeing 777-200's final transmission was a man's voice, probably the pilot's, saying, "Goodnight Malaysian three seven zero."
  • The plane is thought to have crashed into the Indian Ocean and all passengers and crew on board are presumed dead.
  • According to the manifest, there were 239 people on board the plane including 152 Chinese people, 50 Malaysians, seven Indonesians, six Australians, five Indians, four French people and three Americans. Two people were from Ukraine, two from Iran, two from New Zealand, two from Canada and one from the Netherlands, Hong Kong, Russia and Taiwan.
  • The youngest passenger was Wang Moheng, who was 23 months old at the time.
  • The plane's pilot was Zaharie Ahmad Shah, who had an experience with more than 18,000 hours of flying. His co-pilot, Fariq Abdul Hamid, had about 3,000 hours of training.
  • There were reports the plane lost significant altitude after it lost contact with ground controllers. 
  • A massive search operation was launched to locate the plane where it lost contact. When officials failed to find pings from the plane's black boxes, search teams decided to expand the area. 
  • Despite the multimillion-dollar search, the plane was not found. However, there were several false reports of plane debris being found.
  • The biggest lead in the investigation came when a plane flaperon was found by villagers on Réunion Island. Later, authorities confirmed the flaperon belonged to the missing jetliner.
  • In the following months, several possible debris were found but none were confirmed to be from Flight MH370. 
  • Blaine Gibson, an independent wreckage hunter, found several plane debris most of which were believed to be from the missing Malaysia Airlines.
  • As of 2017, three items of debris was confirmed from MH370 — the right flaperon, a part of the right outboard flap and a section of the left outboard flap.
  • While the search for the plane continued, several conspiracy theories surfaced with some saying the pilot deliberately crashed the plane while others hinted at a hijack. However, authorities confirmed none of the theories.
  • Despite several efforts the main wreckage of the plane is yet to be found and the mystery surrounding the jet's disappearance continues.
  • Last year, the search operation for the plane was called off, a move that angered the families of those on board the jet.
  • In January this year, Ocean Infinity took up the charge to find the plane. 
  • The Seabed Constructor vessel has covered 6,178 square miles of the search but has yet to identify any significant findings.