USA pilot unions later said they were not aware of the new anti-stall system.
The stall-prevention system was created to help pilots avoid having to raise a plane's nose too high.
The new feature on the Max 8 and Max 9 models was designed so that the plane's nose does not dangerously rise during flight.
Pilots would only have a few seconds to respond to this situation, aviation experts said, especially if a plane was flying at low altitude, as was the case with Lion Air flight, which plummeted into the Java Sea on October 29.
United States pilots were also not aware of potential risks, two U.S. pilot unions told Reuters.
The Lion Air flight JT 610 had taken off from Jakarta on 29 October and was expected to arrive at its destination at Depati Amir airport in Pangkal Pinang an hour later but it crashed into the sea.
'It is something we did not have before in any of our training.
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Intan Syari lost her fiance in the Lion Air crash, but still went ahead with their planned wedding on Nov 11 this year. The crash resulted in the death of 189 passengers and crew on board.
"We value our partnership with Boeing, but were unaware of some of the functionality of the Maneuvering Characteristics Augmentation System installed on the MAX 8", Feinstein said. More than 200 have been delivered to airlines worldwide, including American, Southwest and United.
Boeing said it is confident in the safety of the 737 Max family of jets.
Boeing and regulators have underscored the steps pilot can take to disable the pitch-trim system, as it's known, in bulletins to 737 Max operators over the past week. The FAA on November 7 issued an emergency airworthiness directive ordering USA airlines to incorporate information about the feature in their pilot manuals.
"What Boeing conveyed to airlines and pilots was that the B737NG and B737 MAX essentially had similar flight-control features", said a senior commander.
He said Boeing bulletins to airlines and pilots "point them back to existing flight procedures" to handle the kind of sensor problem suspected in last month's crash. Still, the response from regulators and pilot representatives hints at a broader reckoning in the commercial aerospace industry over one of Boeing's marquee jets, the 737 MAX8. Capt Mohan Ranganathan, an air safety expert said, "Currently, nowhere in the Boeing flight crew operations manual or the flight crew training manual or the non-normal check-list are these failures listed".
"As we have previously said, we have issued an (airworthiness directive) and will continue to take appropriate action based on what we learn from the investigation".
Indonesian investigators say sensors which help prevent planes from stalling were replaced on the Lion Air plan the day before its fatal flight and may have compounded other problems with the aircraft.