Nearly a year has passed since Malaysia Airlines Flight 370 vanished on a flight from Kuala Lumpur to Beijing, sparking one of the most perplexing mysteries of modern times. Since then, search crews have taken to air, land and sea in a thus-far fruitless hunt for the plane and the 239 people who disappeared with it.
The current phase of the search in the deep, dark and desolate waters of the Indian Ocean has failed to yield a single clue about the plane's fate. Still, despite the lack of fresh leads, the official heading up the search is no less optimistic than when it began.
Here is a look at the latest in the hunt for Flight 370:
Q: How far along is the search?
A: Crews have scoured more than 40% of the priority search zone - a 60,000-square-kilometer (23,000-square-mile) area of the Indian Ocean about 1,800 kilometers (1,100 miles) west of Australia. An international team of investigators who analyzed transmissions between the aircraft and a satellite believe this is where the plane eventually crashed.
Q: How much longer is the search expected to take?
A: Despite occasional delays due to rough weather and equipment snafus, officials believe they're on track to finish searching the priority zone by May.
Q: What happens if they don't find the plane?
A: One option includes expanding the search beyond the priority zone to a wider search area - an imposing, 1.1-million-square-kilometer (425,000-square-mile) stretch of ocean, says Australian Transport Minister Warren Truss. Exactly how long that would take to complete, and how much it would cost, is unknown.
Ministers from Australia and Malaysia - which have each contributed $60 million to the current search effort - will be meeting with their Chinese counterpart next month to decide whether - and how - to fund another search.
"Obviously, the more partners we have in the search, the greater the capacity to search a larger area," Truss says. "And so we'd certainly welcome participation from other countries."
If officials decided to extend the search, they would want to continue using the vessels, crews and equipment currently looking for the plane, Truss says.
Q: How is the search being conducted?
A: There are four ships, each with around 30 people on board, combing the priority zone. Three of the ships are dragging sonar devices called "towfish" just above the seabed to scan for wreckage. In January, a fourth ship, the Fugro Supporter, joined the hunt.
The Supporter is using an autonomous underwater vehicle - essentially an unmanned submarine - that can more easily maneuver along the mountainous, uneven seabed in a few areas the towfish can't fully cover. Unlike the towfish, the underwater drone doesn't send real-time data back to the ship, so crews must haul it up at the end of each 24- to 36-hour mission to download the data.
The ships head back to shore every four weeks or so to get fresh supplies - a trip that takes up to six days each way.
Q: Are searchers still looking for floating wreckage?
A: Technically, yes, says Martin Dolan, chief commissioner of the Australian Transport Safety Bureau, which is leading the search. After studying the area's currents, Australian officials asked Indonesia in August to watch for any debris that might have floated west to the island nation's shores. Officials are now reviewing their drift modeling to see whether they need to revise their projections of where debris could have ended up. But because so much time has passed, Dolan says all surface debris likely sank long ago.
Q: Do the chances of finding the plane in the priority zone become less likely as the search drags on?
A: No, Dolan says, because they haven't been able to pinpoint any areas within the search zone where the plane would have had a higher probability of crashing. Officials could only narrow down the most likely crash site to the 60,000-square-kilometer (23,000-square-mile) priority zone. "Some people think there's a hot spot in there that should be a starting point, but it's pretty much equal priority across that area," Dolan says. "So it's no great surprise that having covered 40 percent, we haven't located it yet. It might be down to the last 1 percent before we do."
Q: What happens if they find the plane?
A: Australia recently asked for expressions of interest from companies with equipment capable of retrieving wreckage from the seabed, which is an average of 4,000 meters (13,000 feet) deep. But bringing it to the surface would be complex.
Search officials would first need permission from the governments involved - namely Malaysia and Australia - to retrieve the wreckage. Then they would have to figure out the best way to do so.
Officials would need to map the area, photograph the debris and get specialized vessels, crews and equipment to the remote search site. All told, Dolan estimates that if the plane is found on the seabed, it would be at least a month before the recovery process even begins.
Q: If the plane is found underwater, what kind of condition would it be in after a year?
A: Although pressure on a plane deep in the ocean would be extreme, currents at those depths would be relatively mild - meaning there's no real concern about debris continuing to scatter once it hit the seabed. After studying the condition of the wreckage from Air France Flight 447, which was found at a similar depth two years after crashing into the Atlantic Ocean, officials think any underwater debris from the Malaysian plane would be relatively well-preserved.
"It's not going to be a pristine aircraft," Dolan says. "But for our purposes, we expect that the aircraft remains will be in satisfactory condition."
Q: Do officials still think they'll find Flight 370?
A: Dolan, who all along has expressed "cautious optimism" that they will find the plane, says his feelings haven't changed. If anything, he leans more toward optimism than caution these days.
He's cautious because of the scant data that led them to focus their search on the Indian Ocean. "This is hugely dependent on technical analysis of quite limited satellite information," he says. "We're always as confident as we can be in the reliability of that, but we have to remind ourselves it's not certain - it's only highly likely."
Conversely, he's optimistic because he is confident in the search crews and equipment, and the high quality of data they're getting from the sonar.
"If the aircraft is out there," Dolan says, "we will find it."