The US is still flying Boeing 737 Max 8 planes, despite a growing number of nations grounding them following two crashes in less than five months. (NPR is keeping track of the countries and airlines that have grounded the planes so far.) But airline pilots on at least two US flights say they have indeed experienced problems flying that type of aircraft, the AP reports. Though official causes have not yet been determined for either October's Lion Air crash in Indonesia or Sunday's Ethiopian Airlines crash—and no link between the two has been confirmed—many have theorized the plane's anti-stall system played a role. In both crashes, the planes noses tilted down suddenly. And in two safety reports filed voluntarily last year, which do not publicly reveal airline, pilot name, or location, two US pilots reported having that same issue.
In the two US cases, the pilots said that soon after engaging autopilot, the nose tilted down sharply; autopilot was disconnected in both instances and the pilots recovered quickly. The captain in one report wrote that "with the concerns with the MAX 8 nose down stuff, we both thought it appropriate to bring it to your attention," and theorized a brief weather system overwhelmed the plane's automation and led to an "airspeed fluctuation"; in the other report, the co-pilot wrote that he and the pilot "can't think of any reason the aircraft would pitch nose down so aggressively." It was not clear whether the airlines or the FAA took any action after the incidents. American Airlines and Southwest Airlines operate the 737 Max 8, and United Airlines flies the Max 9, a slightly larger version. (More on the anti-stall system here and here.)