Some production slots go unfilled, and AI brokers very often don't buy the aircraft from the empty production slots (to place them on Used Market).
This feature would be a variation of "New" order, where the order would be for slots not otherwise available for new orders (first 2-4 months).
In order to limit this feature from abuse, it would be limited to 100% upfront Direct Purchase, so that it is available only in later stages of the game when players have cash (mainly for fleet transitions) and it would not affect any other players' ability to place new order aircraft.