Military GPS Avionics Receivers for Civil Airspace Operations

Allen Edwards and Paul Braisted

Abstract:	The Federal Aviation Administration (FAA) has developed certification procedures for GPS airborne receivers using the Standard Positioning Service (SPS) for Instrument Flight Rules (IFR) operation in the National Airspace System (NAS), embodied in Technical Standard Orders (TSO’s) C129a, C145, and C146. Military aircraft routinely fly in the NAS and until recently have generally used the same equipment as civil aircraft. Now GPS is increasingly being adopted for navigation in the civil airspace and since military aircraft are becoming increasingly equipped with Precise Positioning Service (PPS) GPS receivers for military use, the military would like to use the same receivers to operate in the NAS. However the users cannot currently use the PPS receivers for IFR flight because they are not FAA certified. One approach to meeting FAA certification requirements has necessitated an SPS/PPS switch in the PPS receiver allowing either mode to be invoked. Because institutional agreements have been reached between the FAA and the DoD only for SPS, the aircraft operator is required to switch the receiver to SPS mode to operate in the NAS. While this approach is acceptable as a temporary solution, it would be desirable in the long run for the DoD to set up the necessary procedures and standards to enable military aircraft to utilize the PPS in civil airspace. DoD is exploring means of achieving this capability. It is likely that future military certification will be based extensively on the FAA certification procedures, notably the use of RTCA DO-178B processes for the development of embedded receiver software, and the use of DO-160 standards for hardware testing. Trimble has taken the approach of developing military GPS receivers in accordance with FAA certification rules, ensuring a consistent set of software and hardware development processes between its military and civil airborne receivers. The current TA-12, a 12-channel ARINC-429-compatible GPS sensor, is a SPS/PPS receiver with the capability to switch between modes. It is FAA-certified for operation in the SPS mode. Additionally, going forth military receivers will be required to have Selective Availability / Anti-Spoof Module (SAASM) capability, which requires the use of a highly secure Multi-Chip Module (MCM) inside the receiver. To meet these requirements, Trimble is developing a family of SAASM-based GPS receivers developed to FAA certification processes while retaining Navigation Warfare (NAVWAR) capabilities, in particular the TA-12S, the Force 5 GRASM-S, and the Airborne SAASM Receiver (ASR) card. This paper will address the certification challenges for military receivers, review the alternatives, and focus on the impact of adding certification requirements to the receiver design and development processes.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2486 - 2497
Cite this article:	Edwards, Allen, Braisted, Paul, "Military GPS Avionics Receivers for Civil Airspace Operations," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2486-2497.
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