AILSA CHANG, HOST:
There's more bad news for Boeing. The company is back on the defensive after admitting over the weekend that a safety sensor on its troubled 737 Max planes didn't work as intended. And anger is intensifying because Boeing didn't tell airlines about that until after the first of its planes crashed last October. All of that is ratcheting up pressure on Boeing as it tries to get its grounded 737 Max planes back in the air.
We're joined now by NPR's Russell Lewis, who's been following this part of the story. Hey, Russell.
RUSSELL LEWIS, BYLINE: Hi there.
CHANG: So what do we know about this sensor and why it didn't work properly?
LEWIS: Well, this is called the angle of attack disagree alert. This plane has two angle of attack sensors, one on each side of the nose. And they're designed to tell the flight crew how the plane is flying relative to airflow over the wing. If the angle of attack gets too high, the plane's wing can stop flying and enter an aerodynamic stall.
But the 737 Max had this new flight control system that we've heard about called MCAS. It would force the nose of the plane down in certain circumstances. And this is what is appeared to have happened in the two crashes of the 737 Max. And we should remember that those accidents have killed a total of 346 people. And here's what's new - that in 2017, Boeing learned a few months after the jets began flying, that the sensor would only work if airlines had purchased an optional safety alert.
CHANG: And do we know why Boeing chose not to inform the airlines right away that the sensor wasn't working properly?
LEWIS: Well, this is not a good look for Boeing. I mean, the manufacturer, as we have been reporting, is subject to several congressional investigations, whistleblower complaints and lawsuits that are filed by family members of those killed in the crashes. So clearly Boeing is being careful in what's being said publicly. We really don't know why it took almost a year for Boeing to tell the airlines about it.
But we also have learned that Boeing didn't tell the Federal Aviation Administration about the nonworking sensor until this past November, after that first crash. And at the time, the FAA deemed it, quote - what they're saying is low-risk and that it would be updated by a software upgrade at some point in the future.
CHANG: And what's been the reaction today from all the airlines after this latest news?
LEWIS: Well, I think anger is probably an understatement.
LEWIS: The airlines, Boeing and the FAA had been working through various issues since the 737 Max was grounded back in March. Things were sounding like they were all in lockstep, working together. But we've continued to see revelations and developments like this one. Earlier today, I spoke to Dennis Tajer. He's the pilots union representative for American Airlines who also flies the 737 Max. And he's very disturbed.
DENNIS TAJER: It shatters the eggshell of the trust that we had built. We were hoping that that would be broadened and bolstered and strengthened as these positive interactions with Boeing happened. But news like this - to say that we're dismayed would be a complement to it. We're just floored by this.
LEWIS: That said, Tajer, Ailsa, says that he remains optimistic that they can iron out these problems and hopefully at some point get that jet flying again. But you know, he says these continued revelations certainly do not build a lot of confidence.
CHANG: Yeah. How critical is this sensor to making this plane operate properly?
LEWIS: Well, I think that's an interesting question because, I mean, certainly for decades, planes have flown just fine without an angle of attack disagree alert. And Boeing is quick to point out that it's really not an integral safety component of the 737 Max either. But it is a tool that helps pilots understand what's happening to their jets, especially in an emergency situation just 'cause it gives you more data, which really points to sort of a bigger, philosophical issue - the high automation and computerization of these planes.
Clint Balog teaches at Embry-Riddle Aeronautical University in Florida. He's both a pilot and an engineer. And he says there's a problem in aviation right now with what he terms data saturation.
CLINT BALOG: We can provide a flight crew with so much data and information that we can cognitively overload them and provide them with so much information that it actually reduces safety.
LEWIS: And all of this is the backdrop as Boeing works to get its grounded jets back in the air.
CHANG: That's NPR's Russell Lewis. Thanks so much, Russell.
LEWIS: You're welcome. Transcript provided by NPR, Copyright NPR.