All Boeing 737 NG and Classic planes that have not been used in seven days are now required to be inspected before use. If rust problems are found, the valves must be replaced, the FAA requires.
The demand comes after four reports of engine problems that must have arisen due to rusty air valves stuck in the open position instead of closing.
Boeing confirms that the valves are more susceptible to corrosion when not used for a long time. The company urges all operators with the aircraft in question to inspect their aircraft, and offers assistance should any problems be found.