At that time, the issue was the so-called FSX, an advanced fighter aircraft Japan planned to design and develop with the assistance of the American manufacturer of the F-16, General Dynamics.
There are those advanced nations who think that developing countries either cannot absorb this assistance, or that will not be held accountable effectively, and that the world's fastest-growing emitters should bear a greater share of the burden.
This detail hardly matters now at a time of such national sorrow, but if it helps explain why a large, modern and technologically-advanced country like Poland was flying such an old plane, perhaps that is of some small assistance.