B737 accident at CJIA
Maybe there was a problem with flaps, maybe it was not going to full 40. so the crew may have attempted to cycle it without success and in the confusion while on final approach may have inadvertently left the lever in the "UP" position with the flaps stuck partially extended. On short final the flap may have slowly started to follow the lever position (UP). This may not have been realised and the pilot (unknowingly) compensated by adding more power to maintain his speed, or the auto thrust system automatically doing so. This would explain the assumed somewhat long and fast landing, and no "Config" warnings since flaps may have been still partially extended (20 or so). On rollout the flaps continued to retract finally reaching full up position just before running off the runway……..plausible, since an inexperienced co-pilot may not necessarly pick this up...Captain flying