This is a great video that does a concise and understandable of the main theory for the issue that occured on the LionAir flight: https://www.youtube.com/watch?

This is a great video that does a concise and understandable of the main theory for the issue that occured on the LionAir flight: https://www.youtube.com/watch?v=zfQW0upkVus https://www.youtube.com/watch?v=zfQW0upkVus It was very helpful for me to understand exactly what "runaway trim" meant. Essentially, it's a force (down or up) on the elevator on the horizontal stabilizer. The pilot still controls it from his yoke, but the more trim applied the more it pushes the result in a given direction. If the system applies trim consistently to push the nose down (to avoid what it thinks is an imminent staff), it will progressively more difficult for the pilot to counteract that and pitch up. Eventually, it's too much to handle. This situation should be easily detectable, from what I understand, due to large wheels moving visibly in the center console, and the pilots can counteract the trim in a known procedure.