Because the Xi'an/Xian uses its flaps for the vectoring angle, it really needs a way to tell which way the 'flaps' are pointing.

If you're flying without extra instruments/hud, it's impossible to know if your 'flaps' are angled or facing down unless you scroll through the action menu - pretty tricky when landing!

Also, once you've changed from min to med flaps, it takes so before you can then change to max, you can't just press the 'flaps up' key and know it will work (same when going from max to med to min) . If it's not been long enough, pressing the button might not be doing anything (but you can't really tell since there's no indicator).