The Federal Aviation Administration has ordered owners and operators of Boeing 737 jets to check some aircraft for loose lug bearings in the tail, according to an Emergency Airworthiness Directive issued Friday.Boeing estimates that the directive affects about 600 aircraft, which need to be inspected within 12 days. Failure of the lugs could cause vibration leading to structural failure of the horizontal fins and flaps in the tail, possibly resulting in “loss of aircraft control and structural integrity,” the agency’s directive said. Boeing issued a related service alert Friday that affected six models of 737s, the company’s biggest-selling jetliner. The...