(CNN) -- A ticking clock. A widening search.
The box containing the flight-data and cockpit-voice recorders of missing Malaysia Airlines Flight 370 has batteries designed to keep it sending out pings for 30 days.
The search is now in its 12th day, covering a total area roughly the size of the continental United States. That leaves 18 days until the batteries are expected to run out.
Investigators hope the recorders may reveal vital information about why the passenger jet carrying 239 people veered dramatically off course and disappeared from radar screens. But they have to find them first.
Searchers from at least 26 countries have a formidable task in pinpointing the plane's location somewhere along two vast arcs, one stretching deep into the Asian landmass, the other far out into the Indian Ocean.
"The odds of finding the pinger are very slim," said Rob McCallum, an ocean search specialist. "Even when you know roughly where the target is, it can be very tricky to find the pinger. They have a very limited range."
Some of the nations involved in the hunt are deploying an impressive array of technology, including satellites and high-tech submarine-hunting planes, as they try to narrow the search area.
They're also trawling through existing radar and satellite data for clues.
Small details emerge
Much of what has emerged in recent days has filled in a few more details about the early part of the missing Boeing 777-200's flight.
But clear information on what went on in the cockpit and where exactly the errant jet went after it vanished from Malaysian military radar remains frustratingly elusive.
On Tuesday, for example, a law enforcement official told CNN that the aircraft's first major change of course was almost certainly programmed by somebody in the cockpit. The change was entered into the plane's system at least 12 minutes before a person in the cockpit, believed to be the co-pilot, signed off to air traffic controllers.
But that disclosure only left more questions about the reason behind the reprogrammed flight path.
Some experts said the change in direction could have been part of an alternate flight plan programmed in advance in case of emergency; others suggested it could show something more nefarious was afoot.
The Thai military, meanwhile, said it had spotted the plane turning west toward the Strait of Malacca early on March 8. That supports the analysis of Malaysian military radar that has the plane flying out over the Strait of Malacca and into the Indian Ocean.
But it didn't make it any clearer where the plane went next. Authorities say information from satellites suggests the plane kept flying for about six hours after it was last detected by Malaysian military radar.
Who was at the controls?
Malaysian authorities, who are coordinating the search, say the available evidence suggests the missing plane flew off course in a deliberate act by someone who knew what they were doing.
Figuring out who that might be has so far left investigators stumped.
Particular attention has focused on the pilot and first officer on Flight 370, but authorities are yet to come up with any evidence explaining why either of them would have taken the jetliner off course.
And some experts have warned against hastily jumping to conclusions about the role of the pilots.
"I've worked on many cases were the pilots were suspect, and it turned out to be a mechanical and horrible problem," said Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation. "And I have a saying myself: Sometimes an erratic flight path is heroism, not terrorism
China says it has found nothing suspicious during background checks on its citizens on the flight -- a large majority of the plane's passengers.
Searchers face deep ocean
Malaysian Transport Minister Hishammuddin Hussein, the country's public face of the search efforts, has repeatedly said at news conferences that little is likely to be established about the mysterious flight until the plane is found.
But in the Indian Ocean, where Australia and Indonesia have taken the lead in the hunt, some of the depths searchers are dealing with are significant.
The Bay of Bengal, for example, which lies between Myanmar and India, has depths of between about 4,000 and 7,000 meters (13,000 feet and 23,000 feet), according to McCallum.
Wreckage and bodies of passengers from Air France Flight 447, which crashed into the Atlantic Ocean in 2009, were found at depths of around 12,000 feet by unmanned submarines.
It took four searches over the course of nearly two years to locate the bulk of the wreckage and the majority of the bodies of the 228 people on board Flight 447. It took even longer to establish the cause of the disaster.
Right now, authorities don't even know for sure if the missing Malaysian plane crashed or landed -- or where.
CNN has talked to more than half a dozen U.S. military and intelligence officials who emphasize that while no one knows what happened to the plane, it is more logical to conclude it crashed into the Indian Ocean.
The officials say there is no evidence that any U.S. satellite data registered an unknown aircraft in any of the Asian countries along the path the plane may have taken. According to these officials, it is overwhelmingly likely if the plane had crashed on land, there would be some evidence of that, and if it had landed, someone would have seen it.
CNN's Evan Perez, Mariano Castillo and Catherine E. Shoichet contributed to this report.