I have no idea how accurate any of these reports about maintenance logs or passenger reports of the problems on the previous flight are
Eye witness reports should always be treated with some level of skepticism. Reports often conflict or contain otherwise dubious details.
For example, there was a helicopter crash in the water near the Pearl Harbor visitor's center a few years ago. It was witnessed by dozens of people and a decent quality video of it was taken as it tried to make an auto-rotation landing, but stalled as the pilot realized his intended landing area was covered with visitors.
Some witnesses reported dark smoke, shaking, and unusual sounds. The video, in contrast, showed no signs of smoke, normal rotor sounds, and little to no visual indication of issues until the blades stalled, it began to yaw, and the descent rate increased rapidly. Other witness reports were fully consistent with the video. In short, some witnesses were reliable, some were not, and some even appear to not simply have missed details, but mistakenly "remembered" things that didn't even occur.
The investigators should be able to parse statements from passengers on the prior flight to pick out the details that are consistent, and especially anything that is consistent with maintenance records or any recorded flight data that might remain.
Although extremely, extremely unlikely, perhaps this is a MS990 repeat, because of the random nosedives. Like many others, I have the same questions for how such a young plane could suddenly nosedive into the sea like flight 610 did.
Potential explanations range from spatial disorientation to mistakes during recovery from an upset to a maintenance or assembly mistake. Examples of each:Tatarstan 363
- probable spatial disorientation, leading to a nose down angle of 75 degrees at time of crashTransasia 235
- Recovery mistakes - crew throttled back the wrong engine after a failure, leading an asymmetric stall and high speed impact.Alaska Air 261
- Maintenance-related failure - the horizontal stabilizer lead screw nut failed, putting the horizontal stabilizer past its proper range of travel, making the aircraft uncontrollable. The crew made what was, as far as I know, an incredible feat of airmanship keeping the aircraft in flight as long as they did, but with the aircraft genuinely uncontrollable, the descent rate averaged 13,000 FPM for over a minute.
For such a young aircraft as the Lion Air 737, insufficient lubrication might be a dubious root cause of a hypothetical failure similar to Alaska 261, but that's not the only possible way a critical failure of the horizontal stabilizer trim actuator or related components might occur. Purely speculative ideas that come to mind range from a metallurgical issue with the ball nut housing or lead screw, to an assembly mistake, to a chafed control wire causing the actuator to drive to an inappropriate position.