<Meines Wissens brauchst Du bis 5000ft keinen Transponder wenn dieser nicht eingebaut oder defekt ist.>

So kenne ich die Regelung auch

Seit Juli 2016 gilt folgendes:

SERA.13001 Operation of an SSR transponder (Regulation (EU) 2016/1185)

(a) When an aircraft carries a serviceable SSR transponder, the pilot shall operate the transponder at all times during flight, regardless of whether the aircraft is within or outside airspace where SSR is used for ATS purposes.

(b) Pilots shall not operate the IDENT feature unless requested by ATS.

(c) Except for flight in airspace designated by the competent authority for mandatory operation of transponder, aircraft without sufficient electrical power supply are exempted from the requirement to operate the transponder at all times.