ORAC:
Afaik that is the so called problem of this decision, which has been thematised as well. How do we deal with any attack occuring? It is the question, which the court gradually left open for politics, just limiting the capability of heavy weapon use.
A single fighter pilot would NOT be able to defend this, because such an order will never be issued by his superiors after this court judgement and therefore it would be an illegal action being performed by the fighter pilot. In the end he would be condemned to watch it. He could of course shoot it down, but he would be dragged in front of a court material for that one and additionally have to live with it.
They interviewed a high rankining Bundeswehr officer on the question how they feel about it and he said that he feels relieved and that his men feel the same way. He said no fighter pilot on this world would like to be ordered to pull the trigger to fire on a civil airliner.
It has happened before and my guess would be that they mentally never recovered from it. So I am not sure whether any of them would fire on a civil target without receiving order to do so. The funny thing about it was that the Bundeswehr official mentioned a civil airliner with 130 people on board as example. Dunno what he might say about an A380 with its full amount of passengers and crew then.
The law generally left open a grey zone, because it limited the state's action capabilities without offering any solution if the case X ever occurs in our airspace. It just tells what the government may not do, but not what it should do instead. The news reporter expressed it nice way during the evening news: "I guess it's the legitimate price we have to pay for our democratic freedoms and the value of human dignity." I just have the wish that others might respect those too (what they of course won't do - I know I am naive).