- Who spoke the last words to air-traffic controllers?
- Why did the plane appear to dip?
- How many pings are enough?
- How deep is the ocean?
New information emerged Thursday in the investigation into the disappearance of Malaysia Airlines Flight 370 and, with it, new questions:
What new have we learned about the final moments of the plane?
Flight 370's pilot, Capt. Zaharie Ahmad Shah, was the last person on the jet to speak to air-traffic controllers, telling them "Good night, Malaysian three-seven-zero," Malaysian sources told CNN. The sources said there was nothing unusual about his voice, which betrayed no sign of stress. One of the sources, an official involved in the investigation, said police played the recording to five other Malaysia Airlines pilots who knew the pilot and co-pilot. "There were no third-party voices," the source said.
That's significant because it would suggest that the captain was working the radio while the first officer was flying the plane.
What about the dip in altitude?
The Boeing jetliner disappeared from military radar for about 120 nautical miles after it had crossed back over the Malaysian Peninsula, sources say. This means the plane must have dropped to an altitude of 4,000 to 5,000 feet, a senior Malaysian government official and a source involved in the investigation tell CNN.
Why might that matter?
Experts disagree over what significance the reported dip may hold.
"It looks as though they were doing it to avoid any kind of detection," CNN aviation analyst Peter Goelz said.
But former U.S. Department of Transportation Inspector General Mary Schiavo says it could mean that the cabin lost pressure, and the pilots descended to where they could breathe without oxygen.
Or it could mean that the plane lost communications and was just trying to get out of the way of commercial traffic, she said.
What else have we learned about the Malaysian government's response?
Malaysian air force search aircraft were scrambled about 8 a.m. March 8, hours after the plane lost contact with air-traffic controllers and disappeared from radar but soon after Malaysia Airlines reported that its plane was missing, Malaysian sources told CNN. The aircraft took off before authorities corroborated data indicating that the plane turned back westward and found no trace, a senior Malaysian government official told CNN.
In addition, the air force did not inform the Department of Civil Aviation or search and rescue operations until three days later, March 11, a source involved in the investigation told CNN.
How is the search for the plane coming?
More progress was reported Thursday, when a search plane detected another possible signal -- the fifth so far -- from the locator beacons that were attached to the jet's so-called black boxes when it disappeared early March 8, the Australian agency coordinating the search announced.
"The acoustic data will require further analysis overnight but shows potential of being from a man-made source," said retired Air Chief Marshal Angus Houston, the agency's chief coordinator, on Thursday.
A source with the Australian Department of Defence said the emission was not at the 37.5 kHz frequency consistent with pingers from black boxes but was of a frequency that suggested it was from something man-made.
The source said the sonar buoy technology is being used in an experimental way.
How do the buoys work?
Four Royal Australian Air Force P3 Orions have been modified with the technology to detect signals from the sonar buoys -- or sonobuoys -- which they eject into the ocean.
Once they hit the water, they release microphones that descend about 1,000 feet into the water. Any sound signals they may detect are transmitted to surface floats, which relay them back to the plane, said Jules Jaffe, a research oceanographer with the Scripps Institution of Oceanography.
Though "they're really very high-fidelity microphones," it's still "astounding" that they can detect signals from thousands of feet below, he said.
Jaffe said the sonobuoys are as accurate as the towed pinger locator that has detected other signals considered clues to the plane's whereabouts.
On Wednesday, Commodore Peter Leavy said that each P3 can deploy 84 buoys in a pattern.
Although Leavy said Wednesday that the buoys have sensors that can deploy "at least" 1,000 feet below the surface, the source expressed confidence that the technology has been tested at a much lower depth.
OK, that makes five. When will they have enough to go find the boxes?
There's no such thing as too many data points when looking for a device that could be buried 2.8 miles below the surface in silt tens of meters deep. That's because they can triangulate the hits, searching for areas of overlap in an attempt to narrow the search site.
So, investigators plan to keep hunting until there is no chance that the batteries powering the locator beacons are still working.
When will that be?
The beacons are certified to last 30 days but will probably last at least 35 days, which would be Saturday, according to Chris Portale, director of Dukane Seacom, the manufacturer.
Angus, though, noted Wednesday that the signals appeared to be weakening.
How does Thursday's possible pinger detection differ from the other four?
The other four were detected from equipment towed by a ship; this one was detected from a sonar buoy that was dropped into the ocean and descended to a depth of about 1,000 feet. There, it picked up the possible signal from the ocean depths, which it relayed to a plane flying overhead.
How does the listening differ between what's used by the buoys and what's used by the ship?
Because sonobuoys operate quietly -- untethered to the equipment needed in ships -- any signal they recover would be less likely contaminated by ambient, unrelated noise.
How sure are experts that the detected signals are, in fact, from the pingers?
They were pretty darned sure, though not certain, that the signals detected by the towed pinger locator were legit. One of two signals detected Tuesday was at 33.331 kHz and was pulsed at a 1.106-second interval, according to Houston, who cited a data analysis carried out by experts at the Australian Joint Acoustic Analysis Centre.
That's near the standard 37.5 kHz frequency used by the recorders; the difference is not surprising, given the vagaries of how sound travels under water. "They believe the signals to be consistent with the specification and description of a flight data recorder," he said.
Adding to experts' confidence is the fact that the signals were detected along the missing plane's estimated flight path, which was calculated based on its direction and fuel capacity.
Two other signals were detected nearby on Saturday.
But investigators were still trying to figure out whether the signal detected Thursday by the sonar buoy was linked to the pingers.
From how far can the pingers be detected?
Their range of 2 nautical miles (2.3 miles) is less than the depth of the waters they are believed to be in, which makes the discovery of the signals all the more impressive.
What happens once the pingers are located?
Investigators would use an underwater autonomous vehicle to travel to the ocean floor to reach them, Houston said Wednesday.
Just where on Earth is this happening, and what is it like there?
The searchers are focused on a remote stretch of the Indian Ocean 1,400 miles (2,260 kilometers) northwest of Perth that carries its own challenges.
"It's quite possible that there are currents down there, which could have disturbed the debris," said Leavy, who is coordinating military contributions to the search, on Wednesday. "It has been said we know more about the surface of the moon than our own seabed of our ocean floor. I think that's probably right."
Why don't they bring in more equipment to speed this thing up?
Because needless noise would complicate the search for the audio signals. Even the Ocean Shield is minimizing all its systems, using only the equipment it can't do without, according to Houston. "Everything else is turned off."
And when the batteries are pretty surely dead?
Searchers would send out a Bluefin-21 autonomous underwater vehicle with a more accurate sonar and possibly a camera for mapping the ocean floor, said Leavy.
OK, let's say they get a good fix on the pingers. Then how long before they're brought up?
The device(s) would be transferred to fresh water and then dried before the data they contain would be pulled out, Schiavo said. "Then they'll discover on the FDR what they're dealing with and how much of the wreckage they really have to bring up to solve the mystery."
But don't hold your breath. Houston noted that, when Air France Flight 447 plunged into the South Atlantic Ocean in 2009, killing all 228 people aboard, it took investigators nearly two years to determine the location of the wreckage.
And the tough slogging wasn't over. "They thought they had a good fix, and it took the underwater vehicles 20 days to get to the wreckage," Houston said.
But the efforts paid off. Once that happened, submersible vehicles retrieved the plane's voice and flight data recorders, which led investigators to conclude that a series of pilot errors and their failure to react effectively to technical problems had caused the crash.