It is not yet known what caused the crashes of Ethiopian Airlines Flight 302 on March 10 and Lion Air Flight 610 five months earlier, both after erratic takeoffs. But investigators are looking at whether a new software system added to avoid stalls in Boeing’s 737 Max series may have been partly to blame. Faulty data from sensors on the Lion Air plane may have caused the system, known as MCAS, to malfunction, authorities investigating that crash suspect.

That software system takes readings from two vanelike devices called angle of attack sensors that determine how much the plane’s nose is pointing up or down relative to oncoming air. When MCAS detects that the plane is pointing up at a dangerous angle, it can automatically push down the nose of the plane in an effort to prevent the plane from stalling.

Boeing’s optional safety features, in part, could have helped the pilots detect any erroneous readings. One of the optional upgrades, the angle of attack indicator, displays the readings of the two sensors. The other, called a disagree light, is activated if those sensors are at odds with one another.