>>71
1989年4月
ブッシュ大統領が日米よるFSXの共同開発について合意したと発表

Bush Clears Way for FSX Fighter Deal With Japan
https://www.latimes.com/archives/la-xpm-1989-04-30-mn-2867-story.html
F-16 digital flight control computer, for instance, which just came out last year, will not be released to the Japanese.
A Defense Department official stressed that the United States would not provide Japan with highly sophisticated, top-secret software used in the most advanced F-16 jets. He also said the FSX would not be a better plane than American-built fighters.

FBWなど機密ソフトウェアのソースコードを提供しないのは1989年4月の合意時点で決まった条件
もちろん米議会がゴネてらけどブッシュが強権発動して日米合意案を通した