Jakarta, Indonesia (CNN) Boeing was facing mounting pressure Wednesday over the Indonesia airplane disaster as the owner of the doomed jet joined a US pilots' group in alleging the company failed to warn pilots about the potential hazards of a new safety feature implicated in the crash.

A top Lion Air official told CNN that the manual for Boeing's 737 MAX 8 -- the model that crashed into the Java Sea last month, killing all 189 on board -- did not include a warning about a critical feature that could cause the plane to dive.

Zwingli Silalahi, the Indonesian airline's operational director, said the manual did not tell pilots that in certain situations, the plane's stall-prevention system could automatically trigger a response, such as lowering the airplane's nose, to prevent or exit a stall.

"We don't have that in the manual of the Boeing 737 MAX 8. That's why we don't have the special training for that specific situation," Zwingli said Wednesday.

Investigators are examining whether a sensor on the outside of the plane transmitted incorrect data that could have triggered the stall-prevention system.

The airline's claims come after Boeing was similarly accused Tuesday by the Allied Pilots Association (APA) of withholding information about the potential danger of the plane's new features.

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Lion Air Flight 610 crashed shortly after taking off from the Indonesian capital of Jakarta on October 29. Investigators believe the MAX 8 plane may have experienced problems with several sensors.

Boeing said last week that a safety bulletin issued to aircraft operators in the wake of the crash was merely meant to reinforce existing procedures. Both Lion Air and the APA have now rejected the company's assertion.

"They (Boeing) didn't provide us all the info we rely on when we fly an aircraft," Capt. Dennis Tajer, a spokesman for the APA group, told CNN on Tuesday. "The bulletin is not reaffirming, it's enlightening and adding new info."

Zwingli added that Boeing's safety bulletin did not suggest additional training for pilots operating that aircraft. "We didn't receive any information from Boeing or from regulator about that additional training for our pilots," he said.

Zwingli said that if the result of the ongoing investigation -- conducted by Indonesia's National Transportation Commission, the US National Transportation Safety Board, and Boeing -- found that additional training was necessary, Lion Air pilots would undertake it.

On Wednesday, a Boeing spokesperson said in an email that it could not "discuss specifics of an ongoing investigation" and that the company had "provided two updates for our operators around the world that re-emphasize existing procedures for these situations."

"We are confident in the safety of the 737 MAX. Safety remains our top priority and is a core value for everyone at Boeing," the spokesperson said.

The head of the Directorate of Airworthiness and Aircraft Operations (DOAAO) at the Indonesian Transportation Ministry told CNN that the agency was in the process of intensive discussions about additional training for the pilots who fly the MAX 8 planes, but did not elaborate on what any additional training would involve.

On Tuesday, the APA said while there were no immediate safety concerns about the MAX 8 planes, "the fact that this hasn't been told to pilots before calls into question what other info should we know about this aircraft."

"What seems to have happened here is that a new version or a modified anti-stall capacity was added which pushes the nose down automatically. If it's true, it is beyond comprehension that Boeing did not tell the airline and pilots about this," said CNN aviation correspondent Richard Quest.

He added that if important information hadn't been communicated to pilots, it would be a matter for aviation regulators, rather than individual airlines.

"The issue is how much information to give the pilots about the systems on board so they can respond in an emergency," Quest said, adding that pilots are often overloaded with readouts and signals from multiple devices and monitors that can risk distracting them at the worst possible moment.

Lion Air sensor replaced

Boeing's operational bulletin, released last week, pointed airlines to "existing flight crew procedures" to address any erroneous readings related to "angle-of-attack" (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.

The US Federal Aviation Administration (FAA) later issued its own directive that advised pilots about how to respond to similar problems.

Last week, investigators said the AOA sensor on board the aircraft had been replaced the day before the incident, but problems persisted.

Indonesian authorities confirmed last Wednesday that the 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.

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

The FAA's directive affects 246 Boeing 737 Max aircraft worldwide, with 45 of these operated by US carriers that include Southwest, American and United Airlines.

Voice recorder still missing

More than 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 (FDR) that was pulled off the seabed, some 30 meters under water, on November 1. Preliminary findings suggested there were problems with the airspeed 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 altitude.

After problems were reported with the airspeed 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.