STEVE INSKEEP, HOST:
Did the Lion Air jet that went down last month effectively crash itself? Indonesian investigators released a preliminary report. It's an early look at possible causes of a crash that killed 189 people. And the investigators find that an automatic system on the plane repeatedly pushed its nose toward the ground, even as pilots struggled to correct it. NPR transportation correspondent David Schaper is on the line.
David, good morning.
DAVID SCHAPER, BYLINE: Good morning, Steve.
INSKEEP: What was this system?
SCHAPER: Well, the system is an automated system that is supposed to correct a problem if the plane goes into a stall, what they call an aerodynamic stall. So the nose of the plane has to be angled up a bit to maintain lift. And that's what keeps it in the air. But if the angle gets too high, the plane can then stall. So there's a sensor that monitors that, what they call the angle of attack.
And the problem here appears to be that the sensor was wrong, giving bad information about the angle and saying the angle was too high when it was not. So this automated system was taking over and forcing the nose of the plane down when it should not have. And...
INSKEEP: And this becomes a terrifying scenario. The pilots are repeatedly finding their plane pointing toward the ground.
SCHAPER: Exactly. So the block - the black box data reveals that the pilots tried to correct this over and over again. And every time they did, the system would take over and point the nose down again. And this happened some 26 times according to the flight data recorder in the 11 or 12 minutes the plane was in the air.
INSKEEP: Why would the pilots not simply turn off that automated system?
SCHAPER: Well, they may not have known how to do it. In fact, they may not have even known the system existed or how to operate it at all. The sensor problem, that may be unique to this plane. But pilots at several other airlines, including American Airlines and Southwest Airlines here in the U.S., have complained after this crash that they did not know that these new Boeing 737 MAX planes had this automated system, which is called the MCAS. And they say they didn't have any training on what to do if this sort of rare problem occurred.
Now, Boeing denies this, but they did issue some safety orders updating the information about the system almost immediately after this plane crash and telling pilots what corrective actions they should take. So the planes are deemed safe now. And pilots are comfortable with it now. But they say these pilots may not have known what was going on in the cockpit.
INSKEEP: I just want to sort this through. So the plane starts pointing toward the ground again and again. The pilots keep trying to pull up. It's plausible - we don't know what was in their minds. But it's plausible they didn't even know what was...
SCHAPER: Right.
INSKEEP: ...Pushing the plane down. You're telling me that Boeing says, oh, no. Everybody knew about this system. And yet, Boeing went out of its way to advise people about the system after the crash. How does that make sense?
SCHAPER: Well, what Boeing is saying is that this was part of the safety manuals that they give pilots when they have a new model of the plane. But this was a completely different system than previous models of the 737. They - the information that they pushed out then, they say, was just reiterating what you already should have known.
And it does appear that some pilots knew what to do. This plane had trouble before, this exact problem with this sensor. And several other pilots were able to disengage the system, turn it off and take corrective action and keep the plight - the plane from getting into any serious danger.
INSKEEP: I'm wondering if this is like those legal contracts you're supposed to accept when you get a new app on the phone or whatever. There's a ton of information that goes to a new pilot, and maybe they don't necessarily absorb every bit of it.
SCHAPER: Yeah. Well, there were some manuals that pilots have produced that showed that the information was not complete at the very least. So...
INSKEEP: Oh, the information wasn't there.
SCHAPER: Yeah.
INSKEEP: OK. David, thanks for your reporting - really appreciate it.
SCHAPER: My pleasure, Steve.
INSKEEP: That's NPR's David Schaper. Transcript provided by NPR, Copyright NPR.
