This explains a bit about how the THS works: https://www.skybrary.aero/index.php/Trimmable_Horizontal_Stabiliser https://www.skybrary.aero/index.php/Trimmable_H

This explains a bit about how the THS works: https://www.skybrary.aero/index.php/Trimmable_Horizontal_Stabiliser https://www.skybrary.aero/index.php/Trimmable_Horizontal_Sta... The Rostov-on-Don crash in 2016 appears to have been caused by downwards trimming for 12 seconds. This caused a -1g dive from which the pilots were unable to recover. It's inconceivable they wouldn't have been attempting to pull up with the elevator. You can't not notice -1g. https://en.wikipedia.org/wiki/Flydubai_Flight_981 https://en.wikipedia.org/wiki/Flydubai_Flight_981 Now the final report is not out yet, so it's not clear if the downwards trim was somehow manual (which doesn't really make any sense), or a similar problem to the Lion Air crash. Either way, it's worried Boeing and the FAA enough to issue this AD.