While sitting, bored to tears, intermittently scanning the 'Delayed' display next to my flight, I've looked out of the airport windows.
Out on the stand, amongst the baggage and fuel truck activity, I've seen a technician examining the engine fans with a torch (flashlight), presumably part of a mandatory pre-flight inspection procedure, looking for FOD, cracks etc.
It occurred to me: What does the techie do on a windy day when the fans are spinning too fast to examine by eye? Is there some way of braking the shaft to stop the windmilling?