Further, it disappears after a B Victory at the boss.
For those who dont play, a B-rank victory DONT count as a victory in a Transport mission. You may as well have aborted the mission if you knew you'd get a B rank. Also, Hard mode require you to have a Saiun in your inventory and scrap another plane to obtain the disassembled Saiun you need to bring to the boss node, adding insult to the injury if you did obtain B rank.
In this recent event, i-13 and i-14 were newly available. i-14 is rewarded to the player upon clearing E-3. E-3 is the map with two phases: a transport phase and a normal HP bar phase. But the transport phase requires the player to sacrifice a saiun plane (which isn't a common plane), which will be disassembled for transport. If the player either fails to reach the boss (routed to a dead-end) or fails to score at least an A at the boss... then the planes were sacrificed for nothing.