Military position source challenges for worldwide ADS-B out compliance

Military aircraft program offices face numerous challenges over the next decade as they equip their aircraft to meet Automatic Dependent Surveillance-Broadcast (ADS-B) Out mandates. However, a primary challenge is satisfying the position source performance requirements established in various regulatory documents. This paper describes position source challenges and approaches to dealing with those challenges that can result in satisfying the necessary requirements as well as providing specific advantages to military aircraft programs. This paper covers the work being conducted to create position source standards and approvals for use of Precise Positioning Service (PPS) Global Positioning System (GPS) to provide civil and military navigation and surveillance functions. This includes the creation of a new Military Standards Order (MSO) that will communicate these standards to industry as well as military aircraft programs. Military aircraft need to equip with ADS-B Out equipment in order to participate in civil airspace after 2020 in the United States, Europe, Canada, and Australia. Additionally, many aircraft programs desire to equip aircraft with military Mode 5 Level 2 (M5L2) Out technology, which like ADS-B, periodically transmits position and identity information, except M5L2 Out data is protected using encryption. This paper also describes the ADS-B and M5L2 position source regulations and standards. Most of the ADS-B Out regulations are performance based; however, civil aviation authorities often assume compliance will be achieved through equipment meeting Technical Standard Orders (TSOs) utilizing standard civilian data bus architectures. Military aircraft often operate equipment without a TSO and with a military data bus, such as MIL-STD-1553B. Therefore, civil ADS-B Out standards must be adapted for use by the military. The challenges of selecting and integrating a position source for civil ADS-B Out, as well as for military M5L2, include uncertain position and velocity latency from the GPS equipment. In addition, other challenges exist in the availability of ADS-B parameters, utilizing blended inertial and GPS sources, and ensuring proper design assurance for certification. ADS-B Out and M5L2 Out position source requirements do not conflict, allowing a single position source to be leveraged for both capabilities. Single and dual position source architectures are described along with their comparative advantages and disadvantages. An optimal architecture and certification approach is presented which uses MSOd PPS GPS equipment for ADS-B Out and M5L2 Out. This architecture, if implemented using common standards across multiple aircraft types, could greatly reduce ADS-B and M5L2 development, integration, and procurement costs to military aircraft program offices. In addition, common standards could enhance industry's effectiveness in developing dualpurpose PPS GPS equipment.