Originally Posted by
infrequentflyer789
How did the AD come to be issued though? Is the stuck valve a known risk that was previously thought to be acceptable because 737s were not usually parked up for months, or has there actually been an incident due to this (maybe only on one engine)? Engines need to be regularly run-up on parked aircraft - is that enough to trip this failure mode, has it happened on the ground perhaps?
I saw reported four or so incidents. I can't post links but if you search Alaska N569AS 15th July is one example.