National Transportation Safety Committee Chief Soerjanto Tjahjono told reporters the engine of the aircraft “was still healthy” and the plane flew at high speed when it nosedived into the sea.

“So we can confirm that the impact was high energy that caused the plane to be highly fragmented, broken into small pieces,” Soerjanto said.

The force of the impact tore off the black box’s exterior electronics and some of the recorder’s structure.

But the module holding the data-storage core appears in news photos to be intact and the unit that was found on Thursday should eventually be operable, said James Cash, a former NTSB investigator who has processed thousands of such recorders.

“I’m sure that the memory is going to be great,” said Cash, who retired as the safety board’s chief technical adviser for recorders.

Indonesian President Joko Widodo, who met officers supervising the search operations in Jakarta on Friday, asked the National Transportation Safety Committee to work quickly to uncover the reasons for the crash. “We shouldn’t have any such accidents in the future,” he said. “Passengers’ safety must be made a priority.”

The National Search and Rescue Agency may be close to finding the plane’s main wreckage and cockpit voice recorder, its chief, M. Syaugi, told reporters.

The ocean depth in the area of the crash is about 35 meters, and strong currents and waves are making searches difficult, he said.

Pilots warned Lion Air of airspeed fault on doomed plane on Sunday. It crashed on its next flight

The flight data and cockpit voice recorders, both of which are often referred to as black boxes even though they are painted bright orange, hold information on a plane’s electronics and systems, and also store the pilots’ conversations to aid accident investigations.

More than four days after Lion Air flight JT610 plunged into the sea carrying 189 people, search crews have fished out little other than small pieces of the aircraft, body parts of victims, and personal belongings.

The hunt for clues has evoked images of the years-long and as yet unsuccessful search for Malaysia Airlines flight MH370, which disappeared over the Indian Ocean in 2014.

A silent plunge, then a deafening crash: how Indonesia’s Lion Air tragedy unfolded

While it may take days or weeks before definitive information emerges on the Lion Air crash, the airline has said the plane had experienced problems with sensors used to calculate altitude and speed in its previous flight. The issue was checked by maintenance workers overnight before the plane was cleared for the ill-fated flight, the airline said.

The transport safety committee said Friday it had interviewed the crew of the flight that operated the aircraft from Bali to Jakarta the day before the crash, and was also gathering data from military radar outside the national capital.

Divers are scouring the Java Sea to recover the remains of the plane that plummeted into the shallow waters off Jakarta. They found part of the plane’s landing gear and more aircraft parts on Friday.

“We are finding bigger parts as opposed to only small debris yesterday,” Syaugi said. “Now, we are searching at the right spot.” He added that the agency plans to sweep a wider area from Saturday.

The nation’s transport ministry said it’ll step up checks on aircraft and will ground planes with technical snags that can’t be solved. On Thursday, the ministry ordered the suspension of Lion Air managers in charge of quality control and fleet maintenance, as well as the engineer who cleared flight JT610 for take-off.

The Indonesian government has vowed “strict sanctions” on Lion Air if a probe by the safety board proves negligence on the part of the airline, the ministry said on October 31.

Chilling video shows doomed travellers boarding Lion Air flight

In the early days of flight recorders, which were first required in the 1960s, damage in crashes often hampered attempts to obtain usable data. The earliest models etched lines into foil to show the altitude and flight path. Analogue tape recorders were used to capture sounds in the cockpit.

But the devices in recent decades have been computerised and rely on memory chips that have proven highly reliable.

The frame that holds the protected data module is designed to break away in a crash and the external electronics aren’t functional after being in the water, regardless if they’re intact or not, Cash said. The manufacturer provides tools to obtain the data after an accident, he said.

Based on pictures of the device recovered from the Lion Air plane, Cash identified it as one built by L3 Technologies Inc. He processed a similar unit on the jet that slammed into the Pentagon at high speed on September 11, 2001, and survived the intense blaze that followed.

“That was a pretty hard hit,” he said. “It didn’t hurt it at all.”

Cash said he doesn’t recall ever losing the data contained in that family of L3 recorder models.

The Lion Air tragedy has raised fresh questions about the safety record of a country whose airlines were for years judged too dangerous to fly over Europe. Lion Air was among the Indonesian airlines banned by the EU from 2007 through 2016, according to the Aviation Safety Network database maintained by the Flight Safety Foundation.

Indonesia is comprised of thousands of islands, and its domestic airline market has boomed in recent years to become the fifth largest in the world. Local airline traffic more than tripled between 2005 and 2017 to 97 million people, according to the CAPA Centre for Aviation, and is dominated by flag carrier PT Garuda Indonesia and Lion Air Group.

Carriers have struggled with safety issues partly as a result of the pace of that rapid expansion, as well as issues intrinsic to a region of mountainous terrain, equatorial thunderstorms, and often underdeveloped aviation infrastructure.

Additional reporting by Associated Press