The FAA has issued an Emergency Airworthiness Directive for 737-300 to -900ER aircraft that have been stored or in limited use:
The nut: possible corrosion and sticking of 5th-stage compressor bleed-air check valves due to lack of use. May cause unrecoverable compressor stalls on power reduction (e.g. TOD) and off-airport landings if both engines are affected.
https://www.documentcloud.org/docume...-for-737s.html