(David Transier)Following four incidents that United Airlines dubs “safety events and near-misses,” the carrier has issued a warning to its pilots about “significant safety concerns,” and asking them to cut down on potentially disastrous mistakes. According to the Wall Street Journal, the warning was sent by United’s Sr. VP of flight operations to pilots in early January and cites recent instances — like a plane that would have crashed if the pilots hadn’t executed an emergency maneuver and a plane that was flying with fuel levels below the mandatory reserve threshold — that could have had tragic consequences. These events, in which “the common thread… is that they were preventable,” have “dictated that we communicate with all of you immediately,” reads the bluntly worded memo. In addition to calling out the handful of problem cases, the notice reportedly discusses the safety issues involved with the changing makeup of United’s group of pilots.