Finding the main body of the aircraft, including the cockpit voice recorder and the flight data recorder, would be a significant development for investigators, who are working to determine what caused the nearly new Boeing jet to crash in good weather about 13 minutes after it took off.
The black box could offer investigators their best chance of discovering why such a new jet crashed.
The black boxes of Air Asia QZ8501, which crashed into the Java Sea en route from Surabaya to Singapore on Dec 24, 2014, and killed 162, were found after 16 days of searching.
Relatives are desperate to find traces of their loved ones, but so far only body parts and debris have been found. He said their aircraft maintenance engineer licenses have been suspended.
"I thought it was thunder, but it was different from thunder - 'Boom!' - It was loud", said Dadang Hambali.
"There are (signs) in several positions but none of them is the fuselage", Nugroho Budi Wiryanto, the Basarnas operation deputy said.
"One TV station showed footage of two divers after they surfaced, swimming to an inflatable vessel and placing the bright orange device into a large container that was transferred to a search-and-rescue ship".
Relatives of the missing have been looking through personal items recovered from the sea including rows of shoes, backpacks and wallets.
Indonesia has had almost 40 fatal aviation accidents in the past 15 years, according to the Aviation Safety Network. If all aboard have died, the crash will be its second-worst air disaster since 1997, industry experts said.
Separately, the head of the National Transportation Safety Committee, Soerjanto Tjahjono, told reporters that pings detected by search teams are definitely from the aircraft's flight recorder due to their regular interval. Local airline traffic more than tripled between 2005 and 2017 to 97 million people, according to the CAPA Center for Aviation, and is dominated by flag carrier PT Garuda Indonesia and Lion Air Group.
"He requested to return to the airport for RTB (return to base) but. they updated and flew to Jakarta".
"An RTB was requested and had been approved but we're still trying to figure out the reason", Tjahjono told reporters on Monday.
"We're going to start today to dive at the place where we think the aircraft crashed", said Isswarto, commander of the division of research of the navy of indonesia.
A member of the Indonesian Navy dives at the location of the Lion Air flight JT-610 crash off the north coast of Karawang district, West Java, on Tuesday.
A few minutes into the flight, the pilot asked permission to return to the airport, a request that was granted.
Herson, the airport authority chief in Bali, said the aircraft had encountered a "speed and altimeter" problem but the captain was confident that it was airworthy and pressed on.
In a statement, Boeing said it is providing "technical assistance" to the investigators of the accident.
Rescue workers load up recovered debris of Lion Air flight JT610 onto a truck at Tanjung Priok port in Jakarta, Indonesia, November 2, 2018.