Arlington, Va. — CBS News has obtained audio from the American Airlines pilots' union confronting Boeing about new features to the 737 Max that may have been factors in two deadly crashes. Frustration boiled over during the tense meeting in November 2018, less than a month after the first Max crashed, and four months before the second crash.

"We flat out deserve to know what is on our airplanes," one pilot is heard saying.

"I don't disagree," a Boeing official said.

Last October, Lion Air flight 610 went down off the coast of Indonesia killing 189 people. Investigators believe a faulty sensor triggered the plane's MCAS anti-stall system that repeatedly pushed the plane down.

The pilots at the meeting were angry that system was not disclosed to them until after the first crash.

"These guys didn't even know the damn system was on the airplane — nor did anybody else," one pilot said.

The official, Boeing vice president Mike Sinnett, who does not appear to know he was being recorded, claimed what happened to Lion Air was once-in-a-lifetime type scenario.

"I don't know that understanding this system would've changed the outcome on this. In a million miles, you're going to maybe fly this airplane, maybe once you're going to see this, ever. So we try not to overload the crews with information that's unnecessary so they actually know the information we believe is important," the Sinnett said.

The pilots in the room were not satisfied with that answer. "We're the last line of defense to being in that smoking hole. And we need the knowledge," one pilot said.

Boeing told the pilots it would make software changes, perhaps in as little as six weeks, but didn't want to hurry it.

"We want to make sure we're fixing the right things," the official said. "That's the important thing. To make sure we're fixing the right things. We don't want to rush and do a crappy job of fixing the right things, and we also don't want to fix the wrong things."

That fix was still in development when the second 737 Max crashed in March, leading to the worldwide grounding of the plane. The existence of the audio was first reported by the Dallas Morning News.

Captain Daniel F. Carey, president of the Allied Pilots Association, said the pilots he represents will keep pushing for more information. "American Airlines pilots have been pressing Boeing for answers because we owe it to our passengers and the 346 people who lost their lives to do everything we can to prevent another tragedy," Carey said in a statement. "Boeing did not treat the 737 Max 8 situation like the emergency it was, and that's why we took swift legal action demanding years of records related to the model and are working with lawmakers in Washington to ensure proper oversight of Boeing, the FAA, Airbus, American Airlines and all carriers."