Talk:Summer 2017 Event/@comment-2001:D08:C3:4F2D:5520:B456:5DC6:538D-20170831003001/@comment-29735334-20170831020245

Echoing Luitus before me, yes, it is the effect of "plane deterioration". Fighters got shot down in air battle with enemy fighters, reducing your Fighter Power. Also remember that there are bombers that contribute to total Fighter Power, and these are very vulnerable to being shot down in droves, especially when there are Tsu-classes around, and it further decrease your Fighter Power.

It is a good practice to always have much higher Fighter Power than stated to anticipate this deterioration.