The southern Indian Ocean is a vast, desolate and hostile place churned by relentless currents and vicious storms. It is rarely traversed by air or sea, and anything lost there may never be found. That includes Malaysia Airlines Flight 370.

But those scouring a remote swath of ocean west of Australia received tantalizing clues this week, including new radar data about the plane’s velocity. The data, gleaned from radar between the South China Sea and the Strait of Malacca, suggests MH370 was traveling faster than previously believed, the Australian Maritime Safety Authority said. That means it would have run out of fuel sooner. The agency called this new information “the most credible lead to where debris may be located.” 1

The new lead prompted a sudden change in focus to an area 685 miles northeast of where everyone had been searching. They’d spent much of the week scouring an area 1,600 miles west of Perth, Australia, after satellite images taken Sunday by Airbus Defence and Space and Monday by Thailand’s Geo-Informatics Space Technology Development Agency revealed what might be a debris field.

The shift to yet another area underscores just how perplexing the search has been, and how investigators have been frustrated in their quest for answers. None of the aircraft or ships in the region have found anything of note, and the photos may reveal nothing more than whitecaps or the flotsam so often found at sea.

With little else to go on, investigators have so far relied upon the scant satellite and radar communication the plane had after going dark 90 minutes into its March 8 flight to Beijing with 239 people aboard. Finding a debris field would be akin to a homicide detective locating a body, allowing investigators to begin piecing together, literally and figuratively, what happened.

“Until they find debris,” said Dr. Vernon Grose, a former investigator with the National Transportation Safety Board, “they’re spending all that money on this, and it’s totally useless.”

Investigating an aviation disaster is exponentially more difficult when it happens at sea, and harder still when working in an area Australian Prime Minister Tony Abbott called “as close to nowhere as it’s possible to be.” The search area targeted earlier this week covered 30,200 square miles — an area about the size of South Carolina — in water that plunges to 14,000 feet.

Eleven aircraft and six ships from four countries spent the week searched a region so remote that vessels traversing it can go weeks without seeing another ship. When Australian rescue authorities called for merchant ships in the area to join the search, the closest of them, the automobile transport vessel Höegh St. Petersburg, was two days away. Reaching the search site by air took four hours.

Even Air France Flight 477, which went down about 650 miles off the coast of Brazil with 228 people aboard in 2009, didn’t pose so great a challenge. Authorities knew the Airbus A330’s location four minutes before it hit the water, and they had some idea of what happened even before finding the black box data recorder and the bulk of the airframe two years later.

Grasping at Straws

In this case, Malaysian transport officials–joined by experts from the NTSB, the U.S. Navy, Boeing and others–have only the scantest details to go on. Without debris, never mind the data and voice recorders, investigating the plane’s disappearance is a bit like trying to find a missing person with only a handful of voicemails left over several days and hundreds of miles.

“With any mishap where you’re lacking empirical data, you’re just grasping at straws,” said retired Col. J.F. Joseph, a former Marine Corps pilot and aviation consultant.

The three primary goals of any aviation accident inquiry are determining what happened, how it happened, and why it happened. Until the first question is answered, little headway is made on the others. If investigators don’t have wreckage and conclusive data, they can do little more than make educated guesses.

“Without physical evidence, and a reasonable amount of it, there are going to be a lot of loose ends,” said Don Knutson, an aircraft accident investigator. “Enough loose ends where there is going to be a very inconclusive finding.”

Once the debris is found–and aviation experts remain optimistic at least some will be–ships will carefully collect it, tag it, and bring it to a warehouse or hangar, most likely in Australia.

The lightest, most buoyant pieces, such as seat cushions, sections of the fuselage, and the like, most likely will float or eventually wash up somewhere. Heavier parts like landing gear, engines, and large sections of airframe will sink, more or less directly below the point at which they hit the water. Locating a debris field will further focus the search area for these key components, and authorities almost certainly will, as they did with Air France 447, rely upon remotely operated submersibles to comb the sea floor. This will be particularly challenging, as the southern Indian Ocean has a volcanic and rugged floor and some of the deepest water in the world. It also is a brutally violent place, rocked by some of the most severe weather on Earth.

Before retrieving anything, recovery personnel will be briefed by Boeing, Rolls-Royce (which manufactured the engines), and others on how to pull up major components and minimize the risk of further damaging them. Once those parts are aboard recovery vessels, they will be treated with solvents to arrest the rapid corrosion that comes with submersion in salt water.

In many ways, aircraft crash reconstruction is like the world’s most complicated jigsaw puzzle, with half the parts missing. Everything that can be collected will be carefully reassembled to reconstruct the airplane as thoroughly as possible. This proved vital in the investigation of TWA Flight 800, which crashed off the coast of New York’s Long Island in 1996. Some eyewitness reports suggested it was brought down by a missile. But careful collection and assembly of the wreckage led investigators to conclude that an electrical problem in a fuel tank led to an explosion.

Metallurgists, engineers, and other experts will examine the debris in minute detail. They will be joined by evidence recovery teams and criminal investigators until foul play is ruled out.

Close examination of wreckage will provide key insights. Scorching or soot suggest a fire. The manner in which debris is torn, bent, or otherwise damaged can indicate whether the plane blew apart, broke up at altitude, or hit the water. If evidence points toward an explosion, experts will determine whether the blast was subsonic, suggesting the failure of something like a fuel tank, or supersonic, suggesting a bomb or missile. If wreckage indicates the plane hit the water, it also would suggest the angle and velocity of the impact. An examination of the cabin and cockpit could provide additional clues–if, for example, the oxygen masks were deployed. Individual components will be closely scrutinized for similar clues, and theories tested against identical parts.

Forensic pathologists, odontologists, anthropologists, and fingerprint experts will of course attempt to identify any bodies recovered from the sea and examine them for further clues. Burns and smoke inhalation suggest a fire, for example, and the nature of physical trauma would indicate the force with which the plane hit the water.

A Relentless Search for the Black Box

For all it can tell us about what happened to MH370, physical evidence can’t do much to explain why it happened and how the plane wound up thousands of miles off course. To answer that riddle, investigators must find the black box flight data and cockpit voice recorders. These two items, each a little larger than a shoebox, will be the focus of a relentless search. Investigators spent more than two years combing the sea floor for the black box Air France 447 before finding it 13,000 feet down.

The black box, which is actually orange, records at least 88 flight parameters–including airspeed, heading, attitude, altitude, autopilot engagement, and the position of various flight control surfaces–on a continuous loop for at least 25 hours. Recovering the black box and analyzing the data would allow investigators to recreate the flight in a simulator.

A modern cockpit voice recorder generally runs on a two-hour loop to log an incident in real-time. However, because Air Flight 370 might have flown for hours without any input from the pilot, there may be little recorded beyond the sound of the airplane’s last moments.

To aid the search for these vital components, the United States has dispatched a Bluefin-21 autonomous submarine that can dive to 14,763 feet and the the U.S. Navy’s Towed Pinger Locator 25, a hydrophone that can detect the telltale ping of a black box to a depth of 20,000 feet.

“I’m optimistic that they’ll find something,” Knutson said.

Still, it is a race against time. Locating the devices will only grow harder as the current scatters debris ever further and the electronic beacon affixed to the recorders eventually run out of power, which is expected to happen around April 7. The search will go on, as long as necessary, but will only grow more difficult.

Solving the mystery of Flight 370 will be a long, slow and expensive process. The investigation into Air France 447 took three years and cost hundreds of millions of dollars; the TWA Flight 800 inquiry was no less intensive.

But aviation experts said it is imperative that we learn as much as possible about what happened, both for the families of those who died and for everyone who flies. There is a common refrain in aviation that the rules are written in blood. Every rule and regulation, every policy and procedure exists because someone was injured or killed.

“There’s some good that will come out of it,” Knutson said.

1UPDATED 10:05 a.m. 03/28/14: After this story was posted, the the Australian Maritime Safety Authority announced that it was shifting the search area based on new radar information.

More on Malaysia Airlines flight MH370:

How It’s Possible to Lose an Airplane in 2014

Inside the Nearly Impossible Task of Finding an Airplane in the Ocean

This Underwater Microphone Could Find the Missing Malaysia Airlines Jet

A Startlingly Simple Theory About the Missing Malaysia Airlines Jet