A grounded Lion Air Boeing Co. 737 Max 8 aircraft sits on the tarmac at terminal 1 of Soekarno-Hatta International Airport in Cenkareng, Indonesia, on Tuesday, March 15, 2019. Sundays loss of an Ethiopian Airlines Boeing 737, in which 157 people died, bore similarities to the Oct. 29 crash of another Boeing 737 Max plane, operated by Indonesias Lion Air, stoking concern that a feature meant to make the upgraded Max safer than earlier planes has actually made it harder to fly. Photographer: Dimas Ardian/Bloomberg via Getty Images
PHOTO: Dimas Ardian/Getty Images
A grounded Lion Air Boeing Co. 737 Max 8 aircraft sits on the tarmac at terminal 1 of Soekarno-Hatta International Airport in Cenkareng, Indonesia, on Tuesday, March 15, 2019. Sundays loss of an Ethiopian Airlines Boeing 737, in which 157 people died, bore similarities to the Oct. 29 crash of another Boeing 737 Max plane, operated by Indonesias Lion Air, stoking concern that a feature meant to make the upgraded Max safer than earlier planes has actually made it harder to fly. Photographer: Dimas Ardian/Bloomberg via Getty Images
Now playing
01:54
Report: Off-duty pilot saved Lion Air flight day before crash
Pope Francis meets with Iraq's leading Shiite cleric, Grand Ayatollah Ali al-Sistani in Najaf, Iraq, Saturday, March 6, 2021. The closed-door meeting was expected to touch on issues plaguing Iraq's Christian minority. Al-Sistani is a deeply revered figure in Shiite-majority Iraq and and his opinions on religious matters are sought by Shiites worldwide.
PHOTO: Vatican Media/AP
Pope Francis meets with Iraq's leading Shiite cleric, Grand Ayatollah Ali al-Sistani in Najaf, Iraq, Saturday, March 6, 2021. The closed-door meeting was expected to touch on issues plaguing Iraq's Christian minority. Al-Sistani is a deeply revered figure in Shiite-majority Iraq and and his opinions on religious matters are sought by Shiites worldwide.
Now playing
01:42
Pope Francis holds historic meeting with revered Shia cleric
PHOTO: CNN
Now playing
02:30
Behind the scenes as Pope makes historic trip to Iraq
dr sasa
PHOTO: CNN
dr sasa
Now playing
01:32
Myanmar envoy to UN: It seems like they have a license to kill
meghan markle oprah entrevista harry esposa acusa familia real acoso mentiras inhs lkl max foster_00002717.png
PHOTO: cbs
meghan markle oprah entrevista harry esposa acusa familia real acoso mentiras inhs lkl max foster_00002717.png
Now playing
03:33
CBS releases another teaser for Meghan and Harry's Oprah interview
Now playing
03:49
He feared for his life in Nicaragua. Under Biden's new policy, he's safe in the US
screenshot myanmar funeral on streets
PHOTO: Reuters
screenshot myanmar funeral on streets
Now playing
02:26
Shocking images emerge from Myanmar as military cracks down
Screengrab of Our lady of Salvation Church in Baghdad, Iraq from Ben Wedeman's pkg
PHOTO: CNN
Screengrab of Our lady of Salvation Church in Baghdad, Iraq from Ben Wedeman's pkg
Now playing
03:04
CNN revisits church where massacre occurred ahead of Pope's visit
screengrab Japan oldest woman Olympics torchbearer Kane Tanaka
PHOTO: Source: Kane Tanaka
screengrab Japan oldest woman Olympics torchbearer Kane Tanaka
Now playing
02:43
This 118-year-old woman is set to break Olympic record
Sergey Aleksashenko
PHOTO: CNN
Sergey Aleksashenko
Now playing
01:15
Navalny ally: Of course I'm scared but I cannot hide myself
A split of a Muslim religious leader and the Archbishop of Westminster being interviewed by CNN's Becky Anderson.
PHOTO: CNN
A split of a Muslim religious leader and the Archbishop of Westminster being interviewed by CNN's Becky Anderson.
Now playing
02:14
Pope's Iraq visit is risky. 2 religious leaders explain why it's key
Middle east Iraq Christians pope francis Wedeman pkg intl hnk vpx_00000823.png
Middle east Iraq Christians pope francis Wedeman pkg intl hnk vpx_00000823.png
Now playing
03:44
What's behind the mass exodus of Christians from Iraq?
Screengrab for Paula Hancocks live segment on Myanmar
PHOTO: Twitter
Screengrab for Paula Hancocks live segment on Myanmar
Now playing
03:13
Video shows dramatic escalation of violence in Myanmar
Now playing
03:24
Author describes what happened when ISIS underestimated women fighters
FILE- In this Nov. 7, 2019 file photo, the International Criminal Court, or ICC, is seen in The Hague, Netherlands. The Prosecutor of the International Criminal Court said Wednesday, March 3, 2021 that she has launched an investigation into alleged crimes in the Palestinian territories. Fatou Bensouda said in a statement the probe will be conducted "independently, impartially and objectively, without fear or favor."(AP Photo/Peter Dejong, File)
PHOTO: Peter Dejong/AP
FILE- In this Nov. 7, 2019 file photo, the International Criminal Court, or ICC, is seen in The Hague, Netherlands. The Prosecutor of the International Criminal Court said Wednesday, March 3, 2021 that she has launched an investigation into alleged crimes in the Palestinian territories. Fatou Bensouda said in a statement the probe will be conducted "independently, impartially and objectively, without fear or favor."(AP Photo/Peter Dejong, File)
Now playing
01:57
ICC to investigate alleged war crimes by Israel and Hamas
Attorney-General Christian Porter speaks during a media conference on March 03, 2021 in Perth, Australia. Attorney-General Christian Porter has publicly confirmed he is the cabinet minister named in a historical rape allegation from 1988 which came to light in the last week and has emphatically denied the allegations.
PHOTO: Paul Kane/Getty Images
Attorney-General Christian Porter speaks during a media conference on March 03, 2021 in Perth, Australia. Attorney-General Christian Porter has publicly confirmed he is the cabinet minister named in a historical rape allegation from 1988 which came to light in the last week and has emphatically denied the allegations.
Now playing
02:25
Australian Attorney General denies historical rape allegation
(CNN) —  

An off-duty pilot in the cockpit of a Boeing 737 Max 8 jet jumped in to help crew disable a malfunctioning flight-control system as it experienced difficulties in October, according to Bloomberg.

The next day, with a different crew, the same plane crashed into the sea off Jakarta, killing all 189 people on board.

On doomed Lion Air Flight 610, pilots searched in a handbook for a way to stop the plane from nosediving, according to an exclusive Reuters report.

Reuters cites the information from three people with knowledge of the contents of the cockpit voice recorder that has never been made public.

Indonesia’s National Transportation Safety Committee (KNKT) has refused to comment to CNN on the content of the voice recorder as the investigation is still ongoing. Boeing also refused to comment to CNN on the matter Wednesday.

Indonesian authorities found the cockpit voice recorder in the Java Sea on January 14 and said it could take up to a year to publish a full report into the crash.

A Lion Air Boeing 737 Max 8
PHOTO: Boeing/Lion Air
A Lion Air Boeing 737 Max 8

The revelation that an extra pilot saved the plane the day before the crash has never been reported before, according to Bloomberg.

Aviation analyst and editor in chief of Airlineratings.com, Geoffrey Thomas, said it was not unusual for off-duty pilots, known as dead heads, to fly in the cockpit of planes.

“It could well be that the flight is full and he needs to get back to Jakarta – so as long as he is authorized to do so – then it’s absolutely fine,” he said.

However, the presence of the third pilot in the cockpit did not appear in the National Transportation Safety Committee’s (KNKT) November preliminary report into the crash.

Thomas said this fact should have been reported “as you could argue that the pilot was a distraction or an assistance,” he said.

CNN contacted Lion Air Group Captain Daniel Putut for comment and he directed questions to the KNKT.

Soerjanto Tjahjono, the head of KNKT told CNN on Wednesday they were not aware of the details in the Bloomberg report. CNN continues to reach out to more officials at the KNKT.

Investigators said the jet experienced problems on its last four flights – including, crucially, the flight that crashed, according to Tjahjono.

Indonesian authorities confirmed that the plane’s angle of attack (AOA) sensor was replaced after a flight from Manado, in North Sulawesi to Denpasar, Bali on October 28. The Boeing 737 Max 8 then made another flight to Jakarta that same day, and the pilots reported further problems.

The AOA sensors send information to the plane’s computers about the angle of the plane’s nose relative to the airflow over and under the wings to help determine whether the plane is about to stall.

Software installed on Boeing’s 737 Max 8 planes, called the Maneuvering Characteristics Augmentation System (MCAS), automatically lowers the nose of the plane when it receives information from the AOA sensors that the aircraft is flying too slowly or steeply, and at risk of stalling.

A preliminary KNKT report said the crew of Air Lion Flight 610 struggled to override the plane’s automatic systems in the minutes before it plunged into the ocean. The system pulled the plane’s nose down more than two dozen times, the report said.

The report said the MCAS system was responding to incorrect data transmitted by an AOA sensor. A different flight crew experienced the same issue on a flight from Denpasar to Jakarta the previous day, but had turned off the MCAS and took manual control of the plane, the report said.

Once in Jakarta, a Lion Air technician checked the plane again and gave it the green light to fly on its final flight, from Jakarta to Pangkal Pinang on the Indonesian island of Bangka.

The jet crashed 13 minutes after takeoff.

Experts have pointed to similarities between the Lion Air crash six months ago and last week’s Ethiopian Airlines crash, which killed all 157 people on board. Both were Boeing 737 Max 8 planes that were equipped with the same automated flight software and both crashed minutes after takeoff.

The Ethiopian Minister of Transport said preliminary data recovered from the black boxes of the crash in Ethiopia showed similarities to the Air Lion crash. But the investigation is ongoing.

Following the Ethiopian Airlines crash – the second crash of a 737 Max 8 plane in less than five months – countries and airlines around the world grounded their 737 Max planes.

Boeing insists that the 737 Max 8 is safe to fly.

“Safety is Boeing’s number one priority and we have full confidence in the safety of the Max,” Boeing said in a statement on March 12.

“We understand that regulatory agencies and customers have made decisions that they believe are most appropriate for their home markets. It is also important to note that the Federal Aviation Administration is not mandating any further action at this time, and based on the information currently available, we do not have any basis to issue new guidance to operators.”

With reporting from CNN’s Chris Isidore and Ralph Ellis.