What we know happened in the final 13 minutes of the tragic Lion Air flight.

Families gathered this week at the National Search and Rescue Agency headquarters in Jakarta, Indonesia, desperate for information about the fate of their loved ones following Monday’s Lion Air disaster.

A woman named Feni was among the throng. Her sister was one of the 189 people on board flight JT610 when it plunged into the ocean shortly after taking off from Soekarno Hatta International Airport.

“We are here to find any information about my younger sister, her fiance, her in-law to be and a friend of them,” Feni told AAP on Tuesday.

“We don’t have any information,” she said, as her father wiped away tears. “We’re confused. We hope that our family is still alive.”

The flight departed at 6:20am, bound for Pangkal Pinang, an island east of Sumatra. Thirteen minutes later, the Boeing 737 MAX 8 went down roughly 35 nautical miles north-west of Jakarta, littering the ocean with debris. Photos from the scene capture belongings bobbing on the surface or plucked from the water; wallets, mobile phones, shoes.

The airline confirmed 181 passengers, including three children, were on board, along with six cabin crew and two pilots.

No survivors have been found.

What happened in the final minutes of the flight?

Roughly 19 kilometres after takeoff, the flight made a request to air traffic control to return to the airport, but no emergency was indicated.

Yet, according to air traffic navigation agency, AirNav Indonesia, the plane never turned back, and air traffic control lost contact with the flight shortly afterwards.

What happened next is still being pieced together.

According to data released by flight-tracking website FlightRader24, the Boeing was flying erratically before it disappeared from the radar. While a plane would normally be steadily ascending for the first few minutes of its journey, the ill-fated jet dropped 726 feet (221 metres) over 21 seconds.

Aviation expert, Philip Butterworth-Hayes, told CNN the pattern was unusual, especially given takeoffs like this are usually operated by the plane's automatic systems.

"This shows an unusually unstable vertical flight profile," he told the outlet. "Exactly at the same time as the speed increased there was an altitude dip, which meant that at that point there was quite some loss of control."

So what caused the Lion Air plane to crash?

At this stage it's unclear.

Weather conditions were normal. And piloting the aircraft were Captain Bhavye Suneja and co-pilot Harvino, who had 6000 and 5000 hours of flying experience, respectively, according to a statement by Lion Air.

It's hoped answers will be held within the aircraft's black box flight-data recorder. The crucial device is yet to be found, leaving Indonesia's National Transportation Safety Committee scrambling to piece together what happened to the Boeing 737 MAX 8.

It was, after all, one of the aeronautical company's newest and most advanced jets. The 210-seat model is reportedly used by more than 100 airlines worldwide (none of which are Australian), and this particular aircraft had only travelled 800 kilometres since going into operation with Lion Air on August 15.

What is known, though, is that it had experienced problems the day before the tragedy.

On Monday, Lion Air chief executive Edward Sirait told media the plane had an unspecified "technical issue" on Sunday. However, he insisted it had been resolved.

"If the plane was broken it would have been impossible to clear the plane to fly from Denpasar [in Bali, to Jakarta]," he said. "When we received the flight crew’s report, we immediately fixed the problem."

The crash is not the first blight on Lion Air's safety record. In 2013, a Bali-bound Lion Air Boeing 737 undershot the runway while attempting to land at Ngurah Rai International Airport, and crashed into the ocean. All 108 passengers and crew survived, though several people sustained injuries.

It also comes two years after the European Union lifted a ban on Indonesian airlines entering its airspace. The blacklist was implemented in 2007 amid safety concerns.

What next?

The search continues for key parts of the aircraft as well as the remains of those on board.

According to National Search and Rescue, rescuers have so far used 24 body bags for the remains discovered at the crash site, which have been taken to Kramat Jati Police Hospital for examination and identification.

As authorities continue their investigation, Boeing and Lion Air have offered their full cooperation.

"It is with the hope that the families of the passengers and crew will have the strength and fortitude to go through this challenging time," the airline said.