Board Thread:Questions and Answers/@comment-10993019-20140603233331/@comment-1824272-20140604001437

The non-standard upgrade is a special thing that applies to aircraft at Level 5+.

When you complete research for a level 5 aircraft to level it up to level 6, you have two options:
 * Spend the credits, like you did for the previous levels.
 * Use a Level 5 -> Level 6 non-standard upgrade form.

Those upgrade forms are specifically for Level 6, Level 7, Level 8, Level 9, and Level 10 - each form is different. They're only awarded through challenges or dropped (VERY RARELY) from post-match boxes.

Using an upgrade form is like using it instead of the credits to purchase the next level of an aircraft.

Otherwise, there's no difference between standard and non-standard upgrades.