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More Questions Are Being Raised About Safety System In Boeing's 737 Max Jets


To another story now, pilots for American Airlines will begin training this weekend on software changes to the Boeing 737 Max. These changes are designed to fix problems that may have contributed to the crash of two planes in recent months - the Lion Air jet crash in Indonesia last October and the Ethiopian Airlines crash this month. Software upgrades are being rolled out even as more questions emerge about a safety system designed to prevent the 737 Max from stalling. NPR's David Schaper is tracking all this. He joins me now. Hey, David.

DAVID SCHAPER, BYLINE: Good afternoon.

KELLY: Hi. I want to start with the central baseline question. Do we know yet what caused either crash, and do we know if the same thing caused both these crashes?

SCHAPER: Well, it's both related to that safety system - so we think, anyway. The 737 Max has a safety system that did not exist on previous versions of the plane. It's called MCAS or MCAS, and it's a flight control system that automatically would force the nose of the plane down if it was pitched up too high and entering into what's known as an aerodynamic stall. And it relied on an angle of attack sensor to tell it if the plane was pitched up too high.

Now, what investigators say happened in the Lion Air jet crash in Indonesia is that sensor malfunctioned and provided erroneous information, making the system thinking the plane was about to enter the stall and forcing the nose plane - the nose of the plane down time and time again while the pilots were fighting to regain control. Ultimately, it went into a nosedive. Investigators in the Ethiopian crash say there were a lot of similarities in the sensor data and in the flight pattern in that the pilots were fighting to keep the plane from going into a nosedive. And ultimately, it did.

KELLY: I want to steer you to another thing being reported. This is about this warning system that could have alerted pilots to the problem, but it was an optional warning system, not part of the standard equipment on the plane. What do we know about that?

SCHAPER: Well, sources with - who are familiar with the development of the plane tell me that everything that the pilots needed to have in order to operate the plane safely was included in the baseline configuration of the cockpit. Now, there is a warning light to tell - because there are two of those angle of attack sensors. The MCAS system only used one of them.

But there could be a warning light that would tell the pilots if the angle of attack sensors disagree. And that wasn't necessary, according to the sources I've talked to, because the pilots wouldn't need to take any action just based on that info. What they didn't count on is a bad sensor providing bad information that would make the plane think it's going into a stall and taking this automatic action in the way it apparently did in the Lion Air crash, at least.

KELLY: OK. So meanwhile, we have - these investigations are underway. We're also, as we mentioned - we've got fixes - software fixes being rolled out. Where is Boeing now in trying to address things?

SCHAPER: Well, what they're - they're making some changes to the software of the MCAS system, and they're also going to add this feature - this warning light - if the sensors do disagree. They're trying to do everything they can to kind of put fears at ease and reassure people that this plane can fly properly. That's one of the reasons they're having some pilots come out to Renton, where the plane is manufactured. And they're going to start doing some testing and some - taking some training on the new software changes so they can feel more comfortable about the operation of the plane.

KELLY: That is NPR's David Schaper. He covers the airline industry, reporting there from Chicago. Thanks so much, David.

SCHAPER: My pleasure. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

David Schaper is a correspondent on NPR's National Desk, based in Chicago, primarily covering transportation and infrastructure, as well as breaking news in Chicago and the Midwest.