Armored Platework is a technology that can be researched at the Airbase in Tech Level 4. It costs 350 Carbon and 200 Nova, and gives aircraft +4 armor. It is available to the Rebel Alliance, Republic, Royal Naboo, and Wookiees.
This is a useful improvement for keeping aircraft alive longer, but for most of them, the Shield Modifications grants a better protection, and should be researched first.
"At Tech Level 4, you may research this advanced, lightweight armor that makes your Aircraft much more resistant to enemy fire."
—Manual description