On July 24 CAAC issued an emergency directive, requiring domestic airlines to inspect the engine bleed 5th stage check valves of Boeing 737NG and 737CL aircraft. By 17:00 on July 28, 1 397 Boeing 737NG and 737CL aircraft had been checked, of which 73 aircraft which needed to be inspected had been inspected.

On July 23, the Federal Aviation Administration ((FAA) issued an Emergency Airworthiness Directive AD 2020-16-51, requiring inspections of the engine bleed 5th stage check valves of Boeing 737NG (including 737-600/-700/-800/-900) and 737CL (including 737-300/-400/-500) aircraft, to prevent engine shutdowns as a result of valves sticking in the open position due to corrosion. This AD does not apply to Boeing 737MAX aircraft.

On July 24, CAAC issued a corresponding Emergency Airworthiness Directive CAD2020-B737-09, requiring domestic airlines to inspect the valves and have them replaced if needed. This AD covers Boeing 737NG and 737CL aircraft that are stored for more than 6 days and are operated for 10 or fewer flight cycles.

Following the principle of “maintaining zero tolerance toward hidden safety hazards”, CAAC issued a notice on July 26, requiring domestic airlines to finish inspecting the valves by 17:00 on July 28, and replace them if any inspection is not passed.

There are a total of 1397 Boeing 737NG and 737CL aircraft in China, including 73 which need to be inspected. By 17:00 on July 28th, inspections of the 73 aircraft had been completed, of which 70 had been confirmed safe and resumed operation, and the remaining 3 had not had their valves replaced due to storage related reasons and spares parts shortage and would go through replacement before their next flight.