Take a look at my reply to other post: Reducing MSFS **CPU** load (Limited by CPU) - #29 by geloxo
MSFS needs to be in focus (mouse click or Alt-TAB). If not the FPS readings are giving the ones from Windows desktop. Performance is also impacted as when MSFS is not in focus you may potentially get more stutters (for instance G-sync produces a worse output). Unfortunatelly when you see those FPS increases when going to your Air Manager panels they are not real. That´s because you are getting Windows desktop in focus instead of game, as you are interacting with Air Manager panel app not with MSFS main screen.
I posted a trick below that post. You can change your mouse pointer color to know when you are at desktop or at game. Some things are still allowed: using mouse wheel on another window (so doing zoom at Littlenavmap app for instance) will not take game´s focus to give it to that window, but any mouse click will do it.
I think most people is not even aware of this issue and they may be getting worse results than they should in some situations. Or even the oppossite, thinking that game performs better than it really does, when that´s just a placebo because it´s desktop de one giving such good results. As you see the solution is really simple but you need to remember it: always click once anywhere on MSFS main screen after you finished using other screens or apps.
Cheers