Malaysia Airlines Flight MH370: Three years after aircraft went missing, why hasn't it been found?

One year ago, officials admitted they were unable to find missing Malaysia Airlines flight MH370 and called off the deep-water search for the aircraft, leaving the loved ones of those onboard left to guess their fate and one of the most enduring mysteries of modern times unsolved.

For almost three years, in an operation costing $145m, experts scoured land and sea for the Boeing 777 and were unable to find it or the 239 people onboard. But how can a plane weighing hundreds of tons disappear, and will it ever be found?

That remains to be seen. The Boeing 777 has been missing since 8 March 2014, when it embarked on a routine flight from Kuala Lumpur to Beijing at 12:41am. Less than an hour later the onboard computer sent out its last transmission, showing a normal routing to Beijing. At 11:19am, a voice believed to belong to the co-pilot left the common signing off message "all right, good night". These were the final words from the cockpit heard outside the plane. Three minutes later the plane's transponder, which details altitude and speed to radar systems, cut out.

The plane's signal disappeared from Thai military radar one minute later. Shortly after, a Thai radar station detected an aircraft flying the opposite way to MH370's flight path. Around an hour after take off, Malaysian air traffic controllers lost contact with MH370 over the waters between Malaysia and Vietnam. The last time a radar was detected from the plane was over the island of Pulau Perak in the Strain of Malacca, where it would have been hundreds of miles off course. Exactly what happened on board the flight remains uncertain, although theories that it involved a murder or suicide have been widely rejected due to a lack of evidence.

The resulting search saw experts from Australia, China and Malaysia scour 120,000sq km of sea floor in the southern Indian Ocean – an area decided based on satellite data.

However, some have suggested that the teams looked in the wrong place. The Australian Transport Safety Board, which aided the underwater search, stated in a report published in December 2016 that "everything seems to point a little further east", and suggested a spot to the north of where the flight appeared to veer off. That, they believe, may explain why the aircraft has gone undetected.

"If this area were to be searched, prospective areas for locating the aircraft wreckage, based on all the analysis to date, would be exhausted," they concluded.

The organisation based this recommendation off fragments confirmed to be from the plane that washed up on the shores of the Indian Ocean, and subsequent analysis by the Commonwealth Scientific and Industrial Research Organisation (CSIRO).

A report by the Australian government published in December 2016 also acknowledged that search teams had likely been investigating in the wrong area.

"Given the high confidence in the search undertaken to date, the experts agreed that the previously defined area is unlikely to contain the missing aircraft," a spokesman for the Australian Transport Safety Bureau (ATSB) said in a statement.

David Stupples, Professor of Electronic and Radio Systems at City, University of London, told IBTimes UK there is a 20% chance the aircraft would be found given the errors in position calculation and the topology of the ocean floor in the search area.

Data on the aircraft's course, speed, and known fuel load can give an approximate position on impact to the ocean, he explained.

"However, there are significant errors in this calculation. Firstly, the last registration signal did not align with fuel running out, the aircraft may have flown for several minutes after the last registration signal was received. Secondly, there is an error in doppler measurement. Finally how did the aircraft crash after running out of fuel – did it glide for several miles or crash near vertical?

"Evidence would suggest a more gentle crash since a limited amount of debris was found, and that large parts of the aircraft's control surfaces were found in the Western Indian Ocean. These errors would results in a possible search swathe of 250km by 75km .

"The depth of ocean in this swathe varies but is around 5000m and packed with underwater mountain ranges. So, unmanned submersible vehicles with the most sophisticated sonar would experience significant difficulties in locating an aircraft wreck which could have slipped into a narrow crevice between two underwater mountains."

But the case isn't closed. The Malaysian government has accepted a "no find, no fee" offer from Ocean Infinity, an American private seabed exploration firm, in early January 2018. If the debris field, cockpit voice recorder, or flight recorder are found in the first 5,000sq km the firm searches, the government must award it $20m. This figure will spike to $70m for anything discovered outside the 25,000sq km area.

Regardless of the success of Ocean Infinity, experts are resolute it is vital the plane is eventually found.

Geoffrey Thomas, aviation expert and editor of the Airline Ratings website, told BBC News that it is important for the aviation industry that the plane is found, describing the 777 as "the backbone of the world's international long haul fleet".

Voice370, a group supporting relatives, also told BBC News: "Commercial planes cannot just be allowed to disappear without a trace."