Boeing is currently working on a software fix for its troubled 737 Max jetliner but the challenge for the company is not just to fix the plane's behavior, it also needs to factor in human behavior.
SCOTT SIMON, HOST: Investigators may be getting closer to understanding what went wrong in the crashes of two Boeing 737 MAX jets. Attention is focused on an anti-stall system called MCAS and this week Boeing laid out a proposed fix for that software. NPR's Camila Domonoske has more.</s>CAMILA DOMONOSKE, BYLINE: Even though we do not have final reports on the crashes of the Lion Air jet in October, or the Ethiopian Airlines flight this month, evidence so far has brought attention to MCAS.</s>ANTHONY BRICKHOUSE: The Maneuvering Characteristics Augmentation System is what it's called.</s>CAMILA DOMONOSKE, BYLINE: Anthony Brickhouse is an aviation professor and an experienced crash investigator. He explains, the system only kicks in if the plane's about to stall, to prevent a disaster.</s>ANTHONY BRICKHOUSE: But it looks like in the Lion Air accident there was something going on with the angle of attack indicator or sensor that actually feeds information to the computer.</s>CAMILA DOMONOSKE, BYLINE: And based on the bad data the computer sent the plane down toward the ground. There are signs the Ethiopian Airlines plane may have gone down under similar circumstances. This week Boeing unveiled fixes for the software. The company has been working on them for months, since before the second crash. MCAS used to rely on one data input, now it will take two. Modern airplanes rely on a lot of automation to fly and experts agree that's made them safer. But Boeing can't just make the software better. It also has to grapple with human behavior.</s>CLINT BALOG: They cannot assume that the automation is never going to fail because we know from experience that automation fails, anything manmade fails.</s>CAMILA DOMONOSKE, BYLINE: Clint Balog is a professor of aeronautics. He's a former test pilot who now researches the human factors of flying.</s>CLINT BALOG: You have to look ahead to how they can fail and you have to look ahead at giving the pilots the tools they need to maintain safe control of the aircraft when they do fail.</s>CAMILA DOMONOSKE, BYLINE: In fact, the 737 Max had a system to allow the pilots to take control away from the software. But at least in the Lion Air crash, investigators say the pilots didn't use it. MCAS is new, added for the 737 Max. It was added to correct for how bigger engines changed the plane's center of gravity. But because the system didn't change how the plane handles and pilots could override it with existing procedures it wasn't mentioned in trainings or handbooks. Some pilots were upset to discover they were not told about the system and senators pushed the Federal Aviation Administration on this in a hearing on Wednesday. Here's Senator Ted Cruz of Texas...</s>TED CRUZ: As a passenger I would certainly find it troubling if the captain is describing the training manual as quote, "inadequate and almost criminally insufficient."</s>CAMILA DOMONOSKE, BYLINE: So part of Boeing's fix is about putting power back in pilot's hands with an easier way to override the system and more training. Historically, Balog says, humans taking control has been a big part of Boeing's approach to automation.</s>CLINT BALOG: Boeing has a human-centric automation philosophy in which in most cases the pilot is the ultimate decision maker.</s>CAMILA DOMONOSKE, BYLINE: So making automation easier to overrule is not an unusual step for Boeing, if anything it's a return to form. Boeing says it's working closely with customers and regulators on software and training updates.</s>ASHLEY NUNES: Boeing is certainly on the hook to convince the FAA that the fix ensures public safety.</s>CAMILA DOMONOSKE, BYLINE: Ashley Nunes is a researcher at M.I.T. who studies regulatory policy and transportation safety.</s>ASHLEY NUNES: There have been regulators that have said, you know, until we know what the reasons are for why the airplane actually crashed it doesn't matter what the remedy is that Boeing comes up with, these airplanes are still grounded.</s>CAMILA DOMONOSKE, BYLINE: Boeing continues to stand behind the safety of the 737 MAX, even before the software change. But passengers and regulators need to be persuaded. Camile Domonoske, NPR News.