Newer generations of aircraft in production and use today are equipped with security applications that rely on digital certificates. It is expected that future aircraft will use certificates for increasing numbers of applications. The purpose of this document is to provide guidance for key life-cycle management, which refers to the phases through which digital certificates and associated cryptographic keys progress, from creation through usage to retirement. The guidance is based on open international standards that are adapted to the aviation environment, recognizing that a typical commercial airplane has a long lifespan, its operational environment is highly complex and regulated, and multiple stakeholders operate ground-based systems that communicate with airplanes. Using a standardized and consistent key management approach, as proposed in this document, helps to reduce cost of design, implementation, and operation even across a heterogeneous fleet.