Think The Ukrainian said they are going to Poland to pick it up.
But the thing is, any fighter flew from NATO country to Ukraine may trigger Russian response. (Whether or not they will attack Poland or Germany or anyone is another question) So the aircraft would most likely to be delivered in truck and assemble in Ukraine.
That is probably why they are headed to Germany, I don't think Poland have the facilities to take down the plane.
That's still the same, as they are already engaging Civilian Area. You cannot destroy a Civic center twice....
This is where it gets
LEGALLY dicey.
Convention (V) respecting the Rights and Duties of Neutral Powers and Persons in Case of War on Land. The Hague, 18 October 1907.
CHAPTER I
THE RIGHTS AND DUTIES OF NEUTRAL POWERS
Article 1. The territory of neutral Powers is inviolable.
Art. 2. Belligerents are forbidden to move troops or convoys of either munitions of war or supplies across the territory of a neutral Power.
Art. 3. Belligerents are likewise forbidden to:
(a) Erect on the territory of a neutral Power a wireless telegraphy station or other apparatus forthe purpose of communicating with belligerent forces on land or sea;
(b) Use any installation of this kind established by them before the war on the territory of a neutral Power for purely military purposes, and which has not been opened for the service of public messages.
Art. 4. Corps of combatants cannot be formed nor recruiting agencies opened on the territory of a neutral Power to assist the belligerents.
Art. 5. A neutral Power must not allow any of the acts referred to in Articles 2 to 4 to occur on its territory. It is not called upon to punish acts in violation of its neutrality unless the said acts have been committed on its own territory.
Art. 6. The responsibility of a neutral Power is not engaged by the fact of persons crossing the frontier separately to offer their services to one of the belligerents.
Art. 7. A neutral Power is not called upon to prevent the export or transport, on behalf of one or other of the belligerents, of arms, munitions of war, or, in general, of anything which can be of use to an army or a fleet.
Art. 8. A neutral Power is not called upon to forbid or restrict the use on behalf of the belligerents of telegraph or telephone cables or of wireless telegraphy apparatus belonging to it or to companies or private individuals.
Art. 9. Every measure of restriction or prohibition taken by a neutral Power in regard to the matters referred to in Articles 7 and 8 must be impartially applied by it to both belligerents. A neutral Power must see to the same obligation being observed by companies or private individuals owning telegraph or telephone cables or wireless telegraphy apparatus.
Art. 10. The fact of a neutral Power resisting, even by force, attempts to violate its neutrality cannot be regarded as a hostile act.
Art. 6. If Ukrainian pilots go to any other country to pick up arms, that is allowed. Article 1 remains valid.
Art. 7. Here is where it gets legally questionable. Who is doing the transport?
If I am moving arms for a belligerent thru the neutral power's territory, I am only passing thru
PEACEFULLY. The neutral power have no legal obligation to stop me. Article 1 remains valid.
But it is Poland who is moving arms, the MIGs. Not just anyone's but
POLAND'S OWN MIGS, putting Poland close to being a co-belligerent, aka ally of Ukraine. Article 1 is now at risk.
I think this is why Poland proposed Germany so that articles 6 and 7 will apply to Germany. The problem now is the US with the objection from the Pentagon because the proposal involves Ramstein, a military installation that hosts the USAF. An alternate solution is to use a German civilian airport and cordoned off an area to make the jet transfer.