Hi there,
Just for info, as a Falcon 50/900 driver, I have always been warned about using the S-duct inspection door for a preflight check.
There are very sensitive switches on this door that can cause alarm on warning panel.
Mechanics have proper briefing on this. Pilots usually don't .....
So be very careful when putting it back in place ....
I usually put cover on N°2 engine intake when staying more than one night, except during adverse weather.
Enjoy,
Chris.