A short article translation from ifeng. There is a video with the linked post.
歼-20曾现翼尖擦地险情 歼-31错失展示机会_凤凰军事
Chengdu Aircraft Institute flight control system expert Li Jianping revealed for the first time that one of the prototype J-20's wing tip slightly grazed the ground during landing process. (he didn't say when or which J-20 airframe specifically) He says it was a little scary but the jet landed successfully. The cause was due to a relatively rare phenomenon called pilot-induced oscillation or aircraft-pilot coupling, and they've since came up with several new innovative optimization measures to greatly eliminates the risk of future flights.( Is that the reason why we don't see 2016? )
The article also mention the other Chinese stealth fighter(J-31) had some problem with landing takeoff and resulting in missed opportunities to demonstrate in front of the top leader of the People's Liberation Army. And military experts noted that pilot-induced oscillation is the invisible killer for modern aircraft and the main reason for the landing accidents other than mechanical malfunctions. Both prototype of JAS-39 and F-22 crash were due to pilot-induced oscillation.
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