Excuse me Gaijin. No

Excuse me. This is a flipping PREMIUM PLANE THAT I HAD PURCHASED! The only time you’d need to research parts for a premium IS IF ITS YOUR SELECTED NATION AND BATTLE! Mine WAS BRITISH TANKS!!! NOT AMERICAN PLANES!!!

If it was your first battle after a period of time, this could be catching up on a modification that was changed.

No idea though.

(Edit - I checked mine, and the modification wasn’t researched on it, so it has been added, but also the research wasn’t set so it would give me a chance of getting it randomly in the same manner)

EFS - Engine Firefighting System - was a recent module addition to lots and lots of planes across all tiers.

As such you had to research it, even for premiums, and it “unspaded” a lot of previously “spaded” planes.