Complex sentence: Because directional radiation was required at night time for which a second aerial mast had to be erected, impossible because of the planned (and 1992 opened) new Munich International Airport, the transmitter had to be shutdown at night time.
Split into simpler sentences: Because directional radiation was required at night time, a second aerial mast had to be erected. This was impossible because of the then-planned new Munich International Airport (opened in 1992), so the transmitter had to be shut down at night time.