User blog comment:TenkouKuugen/Small Savings For Improving Type 0 Fighter Model 21/52/@comment-79.33.40.130-20170121231306/@comment-28112544-20170121232410

9 ★  planes upgrade into MAX ★ (as shown in example pic above) and this is what we refer to as "maxed."

If you upgrade a  MAX ★  plane you'll turn it into a different plane.