Jakarta, Indonesia (CNN) Indonesian investigators searching for the flight recorders of crashed Lion Air flight 610 have heard transponder "pings" that could lead them to the devices, and answer questions as to why the new Boeing 737 MAX 8 went down, killing 189 people.

Haryo Satmiko, deputy director of the National Transport Safety Committee, told CNN in a text message that, while the pings had been detected, investigators needed more "technical efforts" to find the exact location of the so-called "black boxes."

Small pieces of debris and remains of some people on board the plane have been retrieved from the water off Jakarta, but the main body of the plane has been missing since it disappeared from radar on Monday around 6:30 a.m. local time.

Lion Air announced Wednesday it has fired its technical director.

The airline gave no reason for the personnel change but said in a news release it was made at "the instruction and the decision of the (Indonesian) transportation ministry."

What we know

FlightRadar24 published data that shows the plane behaving erratically after takeoff from Jakarta to Pangkal Pinang.

Pilots made a request to air traffic control to return to the airport around 22 kilometers (12 nautical miles) after takeoff.

Radar data shows the plane didn't turn around, and the pilots didn't indicate there was an emergency.

Flight crew reported an issue with the plane the night before the flight, and repairs were carried out.

Search and rescue efforts hampered Wednesday by strong underwater currents, officials said.

JUST WATCHED No answers on cause of Lion Air plane crash Replay More Videos ... MUST WATCH No answers on cause of Lion Air plane crash 01:59

Flight data sought

Efforts by divers on Wednesday to confirm the source of the "pings" heard underwater had been impeded by strong currents, according to Indonesia's search and rescue agency BASARNAS.

"We can see something (that) is like a part of the body of the aircraft. And also we can hear the ping locator. But, we don't see the black box yet because the waves under the sea are too strong," BASARNAS chief Muhammad Syauqi told CNN.

Ir. Suryanto, the head of National Transportation Safety Committee, told Indonesian television outlet TVOne on Tuesday that the "pings" had been detected no further than three kilometers from the group of eight current search points.

On Wednesday, Hadi Tjahjanto, commander of Indonesia's Armed Forces, told the same broadcaster that search ships would focus on one particular point that they believe the pings could be coming from.

If those pings are indeed from the plane's flight data recorders, investigators will be able to use the devices to determine what exactly caused the plane to go down.

The devices, often referred to colloquially as "black boxes," record cockpit audio and flight instrument readings.

Soerjanto Tjahjono, Chief of Indonesia's transportation safety committee, said Wednesday that they are "70% sure" the pings are from flight 610's flight data recorder.

Tjahjono told reporters that search and rescue workers detected the noise on Monday, but they needed to bring in special equipment to verify the nature of the signal.

Search-and-rescue operations expanded to at least 400 square nautical miles Tuesday, with divers working to bring passenger remains and debris out of the water.

A group of 100 divers are focusing their efforts on five locations where debris has been identified by sonar equipment --including what could be part of the fuselage -- according to Didi Hamzar, an official with Indonesia's search and rescue agency.

Indonesian President Joko Widodo joined search teams at Tanjung Priok port Tuesday, where debris is being sorted and recorded as part of the investigation into the cause of the crash. To date, no sizable parts of the wreckage have been retrieved.

Indonesia's President Joko Widodo tours the operations centre as recovered debris from the ill-fated Lion Air flight JT 610 are laid out at a port in northern Jakarta.

Images of items fished out of the sea showed wallets, bags and other personal items, including a child's Hello Kitty purse.

At a news conference Tuesday, Muhammad Syaugi of Indonesia's National Search and Rescue Agency said the identification process was proceeding as quickly as possible, but said it was unlikely the remains of all passengers would be found.

Boeing team on site

The Lion Air plane was a brand-new Boeing 737 MAX 8 aircraft.

Lion Air acquired the jet in August and it had flown only 800 hours, according to Indonesia's National Transport Safety Committee (NTSC).

A team of Boeing investigators arrived in Indonesia Wednesday at the request of Indonesia's local regulatory authority, Boeing press officer Kevin Yoo told CNN.

The aircraft is one of the company's newest and most advanced jets, one of 11 such planes in Lion Air's fleet. In a statement, Boeing said the company was "deeply saddened" by the loss and offered "heartfelt sympathies" to passengers and crew on board, and their families.

Indonesian aviation authorities ordered the inspection of 12 other Boeing 737 MAX 8 aircrafts belonging to commercial airlines in the country.

JUST WATCHED Officials don't know why this new plane crashed Replay More Videos ... MUST WATCH Officials don't know why this new plane crashed 02:08

Cause of crash remains a mystery

Flight 610 was carrying 181 passengers, as well as six cabin crew members and two pilots, from Jakarta to Pangkal Pinang, on the Indonesian island of Bangka.

Around 19 kilometers (12 miles) after takeoff, it made a request to air traffic control to return to the airport but did not indicate there was any emergency.

Radar data shows that the plane did not turn back, and air traffic controllers lost contact with it soon after, Yohanes Sirait, spokesman for AirNav Indonesia, the agency that oversees air traffic navigation, told CNN.

Soldiers push inflatable raft as they carry debris of the Lion Air flight JT610 airplane that crashed into the sea, as they walks onto Tanjung Pakis beach in Karawang, Indonesia.

David Soucie, a former safety inspector with the US Federal Aviation Administration, said the fact that an emergency wasn't declared should be a cause for concern.

"What's most peculiar to me is the fact that they didn't declare an emergency. They just simply said, 'We're going back'," said Soucie, a CNN safety analyst.

"But when I look at the track of the aircraft after that, the aircraft made a very steep dive after that which is not typical of what they would've done," he added. "They would have maintained altitude and made that turn and come back to (the airport)."

A pilot who flew the doomed aircraft from Bali to Jakarta the day before it crashed reported a problem with one of the instruments mid-flight, NTSC deputy director Satmiko told CNN. Satmiko had listened to a recorded conversation with air traffic control regarding the problem.

Satmiko said that Lion Air told the NTSC the problem had been fixed.

The airport, runway and weather have been excluded as points of focus for the investigation, he added, and all attention has turned to the aircraft, pilots, other personnel, and Lion Air's company policies.

AirNav Indonesia said the flight would have been given a priority landing spot had it declared an emergency.