As the two-year anniversary of the disappearance of Flight 370 approaches, the situation would seem decidedly grim. The underwater hunt of a punishing patch of ocean that has trudged along since late 2014 has thus far come up empty, the stretch of water left to search is narrowing and skepticism of whether crews are looking in the right place continues to grow.

Still, the man overseeing one of the most complex searches ever conducted seems remarkably unfazed.

"Our best estimate back then was it would take up to two years," says Martin Dolan, chief commissioner of the Australian Transport Safety Bureau, which is heading up the hunt in the desolate waters of the Indian Ocean 1,800 kilometers (1,100 miles) off Australia's west coast. "We were hoping we'd do it more quickly than that. But we knew this was potentially a long game and we planned for the long game."

The ending to that game is now in sight. By late June, crews are expected to finish scouring the entire 120,000-square-kilometer (46,000-square mile) search zone. If they haven't found the Boeing 777 by then, there are no plans to expand the search area. And so the hunt will end — plane or no plane.

With that finality nearing, the ATSB has come under increasing scrutiny over the methods used to determine the search area. Dolan says crews still have a big chunk of ocean to scour — around 30,000 square kilometers (11,500 square miles) — and he remains relatively confident the plane lies somewhere within that patch. "We're not at the point where we're particularly concerned," he says.

But with 70 percent of the search zone covered, the window for success is narrowing, and one question is being asked with increasing frequency: What if they're looking in the wrong place?

Dolan hates hypotheticals. Still, given that he doesn't believe his well-equipped and well-trained crews could drift over the wreckage and miss it, he concedes that if the plane isn't found in the current search zone, it must be because their working theory of what happened on board is wrong.

Malaysia, as the country where the plane was registered, is in charge of figuring out what happened to Flight 370 and why. Australia, as the country closest to where officials believe the plane crashed, is tasked with finding it. But there is necessarily some overlap; Australia had to settle on one of the many theories about Flight 370's fate in order to determine where to look.

The theory the ATSB considers the most probable, based on several factors including satellite data, is that no one was at the controls of the plane when it hit the water. Malaysia long ago said the plane's erratic movements after it took off from Kuala Lumpur were consistent with deliberate actions by someone on board, suggesting someone in the cockpit intentionally flew the aircraft off course. The question Australian officials have focused on is what happened during the latter portion of the flight.

Analysis of exchanges between the plane's engine and a satellite showed the plane flew south on a straight path during its final hours, suggesting it was on autopilot until it ran out of fuel and crashed into the water. Based on that theory, and the location of the final "handshake" between the plane and the satellite, officials calculated the current search area.

Some skeptics have increasingly been pushing an alternate theory: that someone was still controlling the plane at the end of its flight. If that was the case, the plane could have glided much farther, tripling in size the patch of ocean where it could have crashed.

Dolan says officials have always considered that theory, but it is seen as unlikely for several reasons. Among them: The final "handshake" between the plane and a satellite indicated that the aircraft had lost power and it occurred at a point consistent with it running out of fuel. That matters, Dolan says, because if a pilot wants to control the ditching of an aircraft, he or she is trained to do so while there is still power available to the engines. Also, if someone had been at the controls with the goal of maximizing the aircraft's range while crossing the Indian Ocean, the plane could have flown around 300 kilometers (190 miles) farther than the satellite evidence shows it did. That's because pilots use a technique called step climb to alter the plane's altitude in a bid to preserve fuel on long flights.

"All our analysis tells us that by far the most likely scenario is, for whatever reason, that there were no control inputs at the end of flight," Dolan says. "But we have never discounted the possibility of the other scenarios."

As the debate rolls on, so too does the underwater search of the mountainous seabed, which reaches depths of 6.5 kilometers (4 miles). A Chinese ship has just joined the hunt equipped with a state-of-the-art towed sonar device, bringing to four the number of vessels scanning the rugged terrain for wreckage. China's contribution of the ship marks the first time it has agreed to share the financial cost of the search with Malaysia and Australia, which have each pledged $60 million to the hunt. Most of the 239 people on board were Chinese.

Two of the other ships are dragging sonar devices called "towfish" just above the seabed to scan for debris. Another ship, Havila Harmony, has a maneuverable deep-sea drone that has been fitted with a camera and high-resolution sonar for searching difficult terrain and for taking a closer look at areas of interest.

Over the past year, the crews have endured a series of hardships: violent weather, on-board medical dramas that forced the ships to return to port, equipment snafus. In January, one of the towfish crashed into an underwater volcano.

Officials got a rare boost in July when a piece of the plane's wing washed up on Reunion Island on the other side of the Indian Ocean. The discovery of the first confirmed debris from Flight 370 sent a buzz through the Australian search team, Dolan says. This week, authorities announced that an aircraft part that appeared to be from a Boeing 777 washed up in Mozambique; the horizontal stabilizer has yet to be confirmed as part of Flight 370.

An analysis of ocean currents shows that both objects could have drifted from the underwater search zone, bolstering confidence the crews are looking in the right spot.

"There was a noticeable increase in the energy levels in the team," after the Reunion find, Dolan says. "I think it's just because if you plug away on what were essentially mathematical models for a long time, to get something physical that is consistent with what you've been modeling always adds something."

The team hoped that France's analysis of the wing part would reveal clues about what happened at the end of the plane's flight, therefore narrowing the search area. But the analysis hasn't shed any fresh light on that mystery, Dolan says.

As months turn into years, Dolan has had to be cautious about allowing Flight 370 to become all-consuming. He still has an agency to run that is grappling with 130 other investigations, he says. Still, every morning, he checks to see what information came in overnight, eager for good news.

"I always hope I'll get up one morning and we've found it," he says.