Forensics on doomed jets
Probes into two Boeing 737 MAX crashes that left a combined 346 people dead and the model grounded found that multiple factors played a part — but that the tragedies began with the MCAS guidance system.
The software, an upgrade from previous 737 models, is intended to automatically level out a jet if it detects it’s at risk of stalling while ascending at too steep an angle or too slow a speed. But the system can register a false positive if the aircraft gets an inaccurate sensor reading — tilting a perfectly level craft into an unnecessary nosedive.
Pilots have the ability to temporarily toggle MCAS off, but it automatically restarts if further false readings flood the system, effectively creating a tugof-war between the software and the plane’s human crew.
Both Lion Air Flight 610 and Ethiopian Airlines Flight 302 spiraled out of the sky within minutes of their respective takeoffs, meaning pilots had little time or altitude with which to improvise a response.
Indonesia’s National Transportation Safety Commission last week completed its inquiry into the disaster and found that it was compounded by factors including a faulty sensor, inadequate pilot training and the decision to ignore problems the craft had encountered on earlier flights.
The primary cause, however, was MCAS, investigators ruled.
The final outcome is still pending in the Ethiopian Airlines probe, but a preliminary report indicated the crew followed Boeing’s instructions to a T — yet crashed anyway.
The 737 MAX was pulled from global service shortly after the second crash, and Boeing has since labored to work out kinks in the MCAS software.
The model will have to pass rigorous testing before a possible return to commercial service.