(CNN) Problems were reported on a Lion Air jet that crashed into the sea off Jakarta even after technicians replaced a sensor on board the aircraft, investigators said.

Indonesian authorities confirmed Wednesday that the 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.

All 189 people on board Flight 610 died when the new Boeing 737 MAX 8 crashed into the sea on October 29, 13 minutes after taking off from Jakarta on a short flight to Pangkal Pinang on the Indonesian island of Bangka.

Investigators said the jet experienced problems on its last four flights -- including, crucially, the flight that crashed, according to Soerjanto Tjahjono, the head of the National Transportation Safety Committee (KNKT).

Boeing released an operational bulletin on Wednesday, warning all airlines about how to address any erroneous readings related to the AOA sensor. The Federal Aviation Administration (FAA) later issued its own directive that advised pilots about how to respond to similar problems.

Search for voice recorder

Almost two weeks after the crash, authorities are still searching for the plane's cockpit voice recorder (CVR), which is believed to be buried under deep mud. If found, it should reveal what happened in the cockpit in the final seconds of the flight.

Investigators are already examining the flight data recorder that was pulled off the sea bed, some 30 meters under water, on November 1.

Photos: In photos: Lion Air plane crashes off Indonesia A relative of one of the crash victims tosses flower petals from an Indonesian Navy ship on Tuesday, November 6. Hide Caption 1 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Victims' families and colleagues react on a Navy ship as they're ferried to the crash site on November 6. Hide Caption 2 of 27 Photos: In photos: Lion Air plane crashes off Indonesia An Indonesian official examines a turbine engine from the plane on Sunday, November 4. Hide Caption 3 of 27 Photos: In photos: Lion Air plane crashes off Indonesia People in Jakarta grieve over the coffin of a relative on November 4. Hide Caption 4 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Indonesian Navy divers recover a flight data recorder on Thursday, November 1. Hide Caption 5 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Families of the victims look through personal items that were recovered from the wreckage. Hide Caption 6 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A police officer arranges shoes recovered during search operations. Hide Caption 7 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A Navy ship arrives at a search area in the waters of Karawang. Hide Caption 8 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A relative of a passenger cries at a Jakarta hospital on Tuesday, October 30. Family members have been providing authorities with DNA samples to help identify victims of the crash. Hide Caption 9 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Officials transport a body bag in Jakarta. Hide Caption 10 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Indonesian President Joko Widodo inspects debris. Hide Caption 11 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Victims' relatives embrace at a police hospital in Jakarta. Hide Caption 12 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Soldiers drag ashore an inflatable raft containing debris from the plane. Hide Caption 13 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A wallet is seen in the water where the plane went down. Hide Caption 14 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A relative of a passenger cries at a hospital in Jakarta. Hide Caption 15 of 27 Photos: In photos: Lion Air plane crashes off Indonesia President Widodo (front row, second from right) tours the operations center in Jakarta where debris is laid out. Hide Caption 16 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Police work to identify personal belongings that are believed to be from the plane's wreckage. Hide Caption 17 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A police officer studies a map in the search-and-rescue command center. Hide Caption 18 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A diver with the Indonesian Navy enters the water off the north coast of Karawang. Hide Caption 19 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Rescue workers carry a body that was recovered from the waters near Jakarta on October 29. Hide Caption 20 of 27 Photos: In photos: Lion Air plane crashes off Indonesia A woman in Pangkal Pinang prays as she and others wait for news on October 29. Hide Caption 21 of 27 Photos: In photos: Lion Air plane crashes off Indonesia People gather on the beach as a rescue team prepares to leave the coast of Karawang. Hide Caption 22 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Wreckage from the plane lies at a port in Jakarta. Hide Caption 23 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Bagus Sunjoyo, head of airport authority for Soekarno-Hatta International Airport, speaks to members of the media during a news conference. Hide Caption 24 of 27 Photos: In photos: Lion Air plane crashes off Indonesia People watch a rescue team as a helicopter flies overhead. Hide Caption 25 of 27 Photos: In photos: Lion Air plane crashes off Indonesia People look at the passenger manifest for Lion Air Flight JT 610. Hide Caption 26 of 27 Photos: In photos: Lion Air plane crashes off Indonesia Merdiana Harahap is consoled in Medan, Indonesia. Her husband was on the plane. Hide Caption 27 of 27

KNKT is sending a dredger to help with the search for the cockpit voice recorder. It's expected to reach the crash site in the next two days. After initially hearing a "ping" from the recorder on Saturday, diving teams can no longer detect a signal from the device.

"Our obstacle is thick mud that's buried the CVR," said Haryo Satmiko, deputy head of the KNKT. "With this special ship we will suck the mud there and then sweep the area."

Investigators are continuing to interview the pilots, crew and technicians who were involved in the previous flights made by the aircraft in the days prior to the crash.

Unscrambling the jargon

In its statement on Wednesday, Boeing said that the Indonesian transport committee had indicated that Flight 610 had "experienced erroneous input from one of its AOA sensors."

An AOA sensor is an instrument, similar to a small wind vane, that sits outside the plane just below the cockpit and sends information to its computers about the angle of the plane's nose relative to the oncoming air. The sensor helps to determine whether the plane is about to stall and dive.

"It is very important because it tells them if the plane is flying at a too-high angle of attack, which can lead to an aerodynamic wing stall (loss of lift)," said aviation analyst and editor-in-chief of Airlineratings.com, Geoffrey Thomas.

CNN's aviation correspondent Richard Quest said the aircraft receives information from the sensors and responds accordingly.

"The plane's computers were getting erroneous information from external sensors. That caused them to do certain things such as push the nose down. The only way you can handle this is to switch the computer off," he said.

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Problems with air speed indicators

Investigators who analyzed the jet's flight data recorder (FDR) after the October 29 crash said there were problems with the air speed indicator on the past three flights before the crash.

The airspeed indicator is like a speedometer and tells the pilot how fast the plane is moving through the air. It does this by gathering data from the plane's pitot tube and the static port, which essentially compare differentials in the air pressure to arrive at the plane's speed and the altitude.

After problems were reported with the air speed indicator, the AOA sensor was replaced by a Lion Air technician in Bali before the plane departed for Jakarta on its penultimate flight.

Passengers on that flight told CNN that the plane experienced a significant drop in altitude shortly after takeoff. "After 10 minutes in the air the plane dropped as if it was losing power. People panicked. It dropped about 400 feet," passenger Robbi Gaharu 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.

Lion Air Group Managing Director Captain Daniel Putut Kuncoro Adi told CNN on Wednesday that Lion Air strictly follows Boeing's guidance for operating the 737 MAX 8s, as laid out in the maintenance manual book.

"Pilots write in the logbook about the problem they had in the flight, then our technicians fix it and write (what) they did in the logbook," said the managing director, adding that technical conversations between pilots and technicians regarding the aircraft are written and signed in a document called the Aircraft Flight and Maintenance Log.

Quest says investigators will be looking at a combination of factors that could have caused the crash.

"A crash is always a series of events. Fundamentally the issue is going to be how those pilots flew the plane as the conditions arose," he said.

What does Boeing and the FAA say?

On Wednesday, Boeing said it had issued an "Operations Manual Bulletin" advising airline operators how to address erroneous cockpit readings.

A spokesperson for the aircraft manufacturer wouldn't disclose to CNN whether the directive was issued to operators of all Boeing aircraft, or just those who fly 737 MAX 8 planes, the same model as Flight 610.

The directive points operators "to existing flight crew procedures to address circumstances where there is erroneous input from an AOA sensor," the statement said.

The ill-fated Lion Air Flight 610's flight data recorder was recovered from the Java Sea on November 1.

Following Boeing's bulletin, the Federal Aviation Administration (FAA) on Wednesday issued an airworthiness directive to Boeing 737 MAX 8 crews if they experience the same problems that brought down Lion Air Flight 610.

"These erroneous inputs can potentially make the horizontal stabilizers repeatedly pitch the nose of the airplane downward, making the aircraft difficult to control," the directive said.

It continued that, "The FAA has alerted affected domestic carriers and foreign airworthiness authorities who oversee air carriers who use the 737 MAX."

The FAA directive does not acknowledge an issue with the entire fleet of 737 MAX 8 airplanes and there have been no reported comparable issues in the US.

Boeing said it is involved in the ongoing investigation with KNKT and other government authorities into the Lion Air crash and "continues to cooperate fully and provide technical assistance."