Indonesian divers returned Tuesday to a wreckage-littered seabed off Jakarta in their hunt for the black boxes that will likely be key to unlocking the mystery of why a passenger jet carrying 62 people fell from the sky.
Some 3,600 personnel are taking part in the recovery effort, assisted by dozens of boats and helicopters flying over small islands off the capital's coast.
Underwater images from Indonesia's navy showed divers plumbing the murky depths as they combed through twisted wreckage from the Sriwijaya Air Boeing 737-500, which plunged about 10,000 feet (3,000 metres) in less than a minute before slamming into the Java Sea Saturday.
Authorities have so far been unable to explain why the 26-year-old plane crashed just four minutes after takeoff.
But they say they have the approximate location of the black boxes after picking up signals from the devices, which record information about the speed, altitude and direction of the plane as well as flight crew conversations.
Black box data helps explain nearly 90 percent of all crashes, according to aviation experts.
But the boxes could be hidden under layers of mud or plane wreckage in waters about 23 metres (75 feet) deep, and divers have to grapple with a strong current and poor weather.
"They've got to go through garbage and other debris (on the seafloor) and the mud and visibility are also a challenge," Yusuf Latif, a spokesman for Indonesia's search-and-rescue agency, said Tuesday.
The agency deployed a remotely operated vehicle to assist the divers, as investigators examined recovered parts of the wreckage at the port.
- First victim -
Scores of body bags filled with human remains were being taken to a police morgue where investigators hope to identify victims by matching fingerprints or DNA with distraught relatives.
Late Monday, authorities identified flight attendant Okky Bisma, 29, as the first confirmed victim after matching fingerprints from a retrieved hand to those in a government identity database.
There were 10 children among the passengers on the half-full plane, which had experienced pilots at the controls as it left Jakarta bound for Pontianak city on Borneo island on a 90-minute flight.
National Transportation Safety Committee investigator Nurcahyo Utomo said Monday that the crew did not declare an emergency or report technical problems before its dive.
The available data suggested it was "most likely" the plane was intact when it hit the water Saturday, he added.
The crash probe was likely to take months.
Aviation analysts said flight-tracking data showed the plane sharply deviated from its intended course before it went into a steep dive, with bad weather, pilot error and mechanical malfunction among the potential factors.
- Spotty record -
Sriwijaya Air, which flies to destinations in Indonesia and Southeast Asia, has had relatively minor safety incidents including runway overruns, but it has not had a fatal crash since it started operations in 2003.
The Boeing jet that crashed Saturday was previously flown by US-based Continental Airlines and United Airlines.
Indonesia's fast-growing aviation sector has long been plagued by safety concerns, and its airlines were once banned from US and European airspace.
In October 2018, 189 people were killed when a Lion Air Boeing 737 MAX jet crashed near Jakarta.
That accident -- and another in Ethiopia -- led to the grounding of the 737 MAX worldwide.
The 737 model that went down Saturday was first produced decades ago and was not a MAX variant.
In 2014, an Indonesia AirAsia plane headed from Surabaya to Singapore crashed with the loss of 162 lives.
A year later, more than 140 people, including scores on the ground, were killed when a military plane crashed shortly after take-off in Medan on Sumatra island.