There was a new judgement a few years ago:

http://www.zeit.de/politik/deutschland/2013-04/verfassungsge...

Shooting down an aircraft is legal, but only if the cabinett gives the order. Which is still unrealistic, as the Minister of Defence can't order it alone even in an emergency. The judges recognised that this is suboptimal, but a change would need a change in the constitution. Some former ministers of defence are though on record they would still order it and deal with the legal consequences fallout later.

Then there is the question if the pilot alone (I guess that what the tv movie was about?) could make a decision? For example if the aircraft is flying towards a stadium or nuclear plant and the jet pilot has to make a decision in a split second.