MH370: After aborted underwater search, crews hope to try again

Time to try this again.

The first deployment of an underwater vehicle to hunt for Malaysia Airlines Flight 370 was aborted early, sending the drone back to the surface 10 hours before expected.

Search officials analyzed data from the Bluefin-21's six hours underwater, and found no objects of interest, the U.S. Navy said Tuesday.

Crews will try to send the Bluefin-21 probe back into the Indian Ocean later Tuesday, weather permitting.

So what went awry the first time?

"In this case, the vehicle's programmed to fly 30 meters over the floor of the ocean to get a good mapping of what's beneath and to the sides, and the chart we have for the area showed that water depth to be between the 4,200 and 4,400-meter depth," said Capt. Mark Matthews, who heads the U.S. presence in the search effort.

But the water was deeper than expected -- about 4,500 meters.

"Once it hit that max depth, it said this is deeper than I'm programmed to be, so it aborted the mission," Matthews said.

David Kelly, CEO of the company that makes the Bluefin-21, said the device's safety mechanisms have triggered such recalls have happened.

"Although it's disappointing the mission ended early, it's not uncommon," Kelly said. "We've operated these vehicles around the globe. It's not unusual to get into areas where the charts aren't accurate or you lack information."

Mathews said the initial launch Monday night took place "in the very far corner of the area it's searching, so they are just shifting the search box a little bit away from that deep water and proceeding with the search."

It is unclear how much of the area -- 5 kilometers by 8 kilometers (3.1 miles by 4.9 miles) -- the Bluefin scanned during its first attempt. It could take up to two months to scan the entire search area.

The co-pilot's cell phone

While search crews probe the ocean floor, a new detail emerged from the flight.

The cell phone of the first officer of Malaysia Airlines Flight 370 was on and made contact with a cell tower in Malaysia about the time the plane disappeared from radar, a U.S. official told CNN on Monday.

However, the U.S. official -- who cited information shared by Malaysian investigators -- said there was no evidence the first officer, Fariq Abdul Hamid, had tried to make a call.

The official told CNN's Pamela Brown on Monday that a cell-phone tower in Penang, Malaysia -- about 250 miles from where the flight's transponder last sent a signal -- detected the first officer's phone searching for service roughly 30 minutes after authorities believe the plane made a sharp turn westward.

The details do appear to reaffirm suggestions based on radar and satellite data that the plane was off course and was probably flying low enough to obtain a signal from a cell tower, the U.S. official said.

U.S. officials familiar with the investigation told CNN they have been told that no other cell phones were picked up by the Penang tower.

Pilots are supposed to turn off their cell phones before pushing back from the gate.

When the plane first went missing, authorities said millions of cell phone records were searched, looking for evidence that calls had been made from the plane after it took off, but the search turned up nothing.

The suspected oil slick

Another possible clue into the plane's disappearance emerged Monday.

Australian officials announced the Australian ship Ocean Shield had detected an oil slick Sunday evening. It is unclear where the oil came from; a 2-liter sample has been collected for examination, but it will take a few days to analyze.

"I stress the source of the oil has yet to be determined, but the oil slick is approximately 5,500 meters (3.4 miles) downwind" from the area where suspected pings from the plane's "black boxes" were detected.

CNN Aviation Analyst Les Abend, who flies a Boeing 777, said the engines on the plane have about 20 quarts of oil each.

"It could be slowly dripping up to the surface," he told CNN's "Anderson Cooper 360." "They're saying an oil slick. I'm wondering if it's just some sort of a fluid slick. It could be (from) hydraulics."

If it is oil, it's not the first oil slick detected as part of the search. A similar find in the first days of the search was determined to be fuel oil from a freighter.

Surface search nearing end

"The air and surface search for floating material will be completed in the next two to three days in the area where the aircraft most likely entered the water," Houston said.

That search was energized last week when searchers using the Navy-owned pinger locator and sonobuoys detected sounds that could have been from the plane's black boxes, or data and voice recorders.

But after a week of silence, the batteries powering the locator beacons are probably dead, an official from the company that makes the beacons told CNN on Sunday. They were certified to last 30 days, a deadline that's already passed.

That means searchers may not be able to detect any more pings to help lead them to those pieces of the missing plane.