The new search for Malaysia Airlines Flight 370 has reached a critical point, just as the fourth anniversary of the jet’s disappearance on March 8, 2014 is reached.

In what may well be the last chance to solve the mystery the Texas-based deep sea search company Ocean Infinity has so far scoured 8,880 square miles of seabed in an area of the remote southern Indian Ocean selected as the mostly likely site to find the remains of the Boeing 777—without finding anything.

This means that they are very close to having covered the 9,700 square mile primary target area, roughly the size of Vermont, considered the most promising. It includes three specific places identified as “hot spots.”

The search to find an answer to aviation’s greatest mystery that took the lives of 239 people is a race against time: as the Southern Hemisphere winter approaches the sea conditions become steadily worse.

This shows the radical technology deployed by Ocean Infinity’s vessel, Seabed Constructor, in greater detail than any made available before.

The video also discloses for the first time the two data sources on which the new effort is based. The first, already familiar, is derived from the reverse tracking of more than 20 pieces of debris that turned up on beaches in the western Indian Ocean and southern Africa.

The second is an amazing chance discovery made in 2017, that The Daily Beast can now reveal in more detail.

Early in 2017 the French military released images retrieved from one of their satellites that was covering the southern Indian Ocean in late March, 2014, two weeks after the jet disappeared. These images showed a field of debris drifting on the surface some distance northwest of where Australian oceanographers had by then projected that the jet hit the water—in fact, precisely where it would have drifted in the time elapsed before caught by cameras on the satellite.

At the time, resolution on the satellite images was not sharp enough to identify the debris as from Flight MH370, but the Daily Beast has examined a later study by the Australians that shows that they were able to pick out 70 objects of which 12 were identified as probably man-made and 28 possibly man-made.

The convergence of this data, showing where and how that debris would have drifted over the two weeks, with the data derived earlier from modeling the path of recovered debris was so striking that it reinforced the confidence of Dr. David Griffin, leader of the Australian oceanographers, that they had identified the most promising area to search “with unprecedented precision and accuracy.”

It is concerning that with most of this area now searched nothing of significance has been found.

Seabed Constructor uses a swarm of eight highly advanced robots—autonomous underwater vehicles, AUVs. These can sweep the fearsome seabed terrain (including hundreds of volcanoes) at depths of up 3.5 miles for missions lasting as long as 60 hours and cover the area far faster than any undersea technology previously used, and that has been vividly demonstrated by the area covered since early January .

However, this search would not be taking place at all had not Ocean Infinity taken the gamble of committing to it on the basis of “no find, no fee” in a contract with the Malaysian government.

The three nations who undertook the original 27-month search, Malaysia, China (more than half of the 239 people on the jet were Chinese) and Australia, bailed in January, 2017. The Australian government said there would be no new search “in the absence of any credible new evidence leading to a specific location of the aircraft.”

Yet the truth was that Dr. Griffin’s team had at that moment already produced much of the data pointing to the sites now being searched by Ocean Infinity.

The search is by far the most challenging ever faced in seeking the solution to an unexplained air disaster. The new Ocean Infinity video, produced by them to demonstrate the scale of their effort to relatives of the victims, glosses over the harsh reality of the conditions now being faced by the crew and technicians onboard Seabed Constructor. It shows experts in the ship’s command center analyzing detailed images of the seabed as it comes in from the robots. The scene is calm and stable, as though taking place on shore.

But already, at this time of the year, the seas can be seriously emetic in their effects, to say the least. One vessel in the previous search recorded a wave height in the middle of a storm of 70 feet, with only eight to nine seconds between the peak and the trough.

To endure conditions as extreme as these the crew had to be strapped to their bunks and had to frequently take anti-sea sickness medication. Some were injured in falls. In one 28-day mission the conditions were so bad that no searching could be carried out at all.

Ocean Infinity’s deal with the Malaysians promises an award to them of between $20 million and $70 million depending on the extent of the wreckage that is discovered. Finding and recovering the most crucial piece of evidence, the jet’s flight data recorder, is the highest priority.

The Malaysian government has said that the black box and all the debris that is retrievable will be delivered to them and that their officials will be responsible for seeing whether the data in the recorder has survived four years or more at such extreme depths.

But the Malaysians have a poor record of being transparent in dealing with the investigation and the search. The reports they release on the current search are notably perfunctory. In contrast, the reports released on the previous search by the Australian Transport Safety Bureau were more frequent and far more detailed.

Ocean Infinity is committed to a 90-day search, which will be complete, according to their schedule, by the end of April, when the weather window closes in. Once the primary search area is covered the vessel will move further north and cover as much of this unexplored seabed as possible in the time left.

On Saturday Malaysia’s head of civil aviation, Azharuddin Abdul Rahman, attended a remembrance ceremony for the 239 victims held, somewhat bizarrely, at a shopping mall near Kuala Lumpur. He told a group of next-of-kin “The whole world has new hope to find the plane for closure. We want to know exactly what happened to the plane.”