THE SEARCH FOR the black boxes of a crashed Sriwijaya Air jet has intensified to boost the investigation into what caused the plane carrying 62 people to nosedive at high velocity into the Java Sea.

The Boeing 737-500 jet disappeared minutes after taking off from Jakarta, Indonesia’s capital, during heavy rain on Saturday, and the search so far has yielded plane parts and human remains but no sign of survivors.

Authorities have said signals from the boxes containing the cockpit voice and flight data recorders were detected between Lancang and Laki islands in the Thousand Island chain just north of Jakarta’s coast.

Officials said they have marked a location where the sounds were being emitted from the black boxes, which detached from the tail of the aircraft when it plummeted into the sea.

The cockpit voice recorder holds conversations between pilots, and the data recorder tracks electronic information such as airspeed, altitude and vertical acceleration.

When found, they will be transported to port and handed to the National Transportation Safety Committee overseeing the crash investigation.

More than 20 helicopters, 100 navy ships and boats, and 2,500 rescue personnel have been searching since yesterday and have found parts of the plane in the water at a depth of 23 metres, leading rescuers to continue searching the area.

Television footage showed landing gear, wheels and a jet engine among the parts found, while other rescuers brought a dozen body bags containing human remains to a police hospital in eastern Jakarta for the identification process.

The National Search and Rescue Agency chief Bagus Puruhito said divers using high-tech “ping locator” equipment were looking for an identified target beneath 20 metres of seabed mud.

The transport committee’s chairman, Soerjanto Tjahjono, said the black boxes could provide valuable information to investigators.

Once the device is found and taken to the investigators’ facility, it will take three to five days to dry and clean the device and to download its data, Tjahjono said.

Indonesia, the world’s largest archipelago nation, with more than 260 million people, has been plagued by transportation accidents on land, sea and air because of overcrowding on ferries, ageing infrastructure and poorly enforced safety standards.