Electronic architectures in the aerospace domain get more and more integrated and interconnected due to functional and architectural reasons. Such a tight integration raises the need to control information flows between different security domains on-board and off-board aircraft.This paper presents and discusses the specification and implementation of a software architecture of a security gateway integrated into avionics architectures.The paper shows that such a software architecture can be based on the current architectural principles and implementations in the avionics domain. We show that the embedded operating system PikeOS is a possible foundation for such a gateway architecture.