"This emergency AD was prompted by four recent reports of single-engine shutdowns due to engine bleed air 5th stage check valves being stuck open," the FAA said in the directive, which applies to any airplane that has not been operated for 7 or more consecutive days.
The directive covers Boeing Company models 737-300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes.
In March 2019, the FAA grounded the top-selling 737 MAX aircraft following two crashes within five months that killed 346 passengers and crew. Both crashes were blamed on a malfunctioning flight control system that forced planes into nosedives shortly after takeoff.