Aviation Plug-and-Play: The Challenge of Interoperable Software for Aircraft

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The purchase of military aircraft is very complicated because the software on board must not only work seamlessly together but also meet future, ever-changing requirements. The following article explores the solutions to this issue.

The software onboard a (military) aircraft must not only work seamlessly but also meet future and constantly changing requirements. For instance, an agency requests a program with specific operational areas and mission criteria. Based on these requirements, several aircraft integrators compete with one another. These, in turn, compete with various subcontractors for platforms, subsystems, and applications within the program. Once the program is selected, production begins in stages based on demand. Eventually, evolving operational needs lead to a modernization initiative or a new aircraft program—and the entire process starts anew.

Where is the Journey Heading in this Industry?

Here’s another perspective: A service department requires a program that meets specific criteria for operational areas and tasks. Several aircraft integrators offer solutions tailored to the selected requirements. This sounds familiar, but now it gets interesting. Using model-based procurement, these integrators could refer back to previous programs to identify successful platforms, subsystems, and applications. Since they procure software only under the Modular Open Systems Approach (MOSA), it would be possible to select a flight control system from Program A and a cockpit display system from Program B and combine them with a recently developed inertial navigation system (INS) to meet the new mission requirements.

In this scenario, all software would be available in a digital twin, allowing integrators to quickly create a model. For instance, they could import components from existing digital twins along with the new INS subsystem model, enabling them to evaluate the performance, fit, and functionality of the proposed design. Essentially, this model could be used to create a prototype and verify successful software integration.

In terms of project time and costs, this would be a tremendous advantage. Through model-based procurement and digital workflows, this process takes only months instead of years or decades. Since the program uses proven hardware with portable, interoperable, commercial off-the-shelf software (COTS), production could start quickly and without extensive development or retrofitting.

From Theory to Practice

Even though this vision is already on the horizon, a few technological steps are still needed to make it a reality. For instance, model-based systems engineering (MBSE) must reduce the complexity and maintenance of models, digital twins need to enhance integration testing and simulations, and aircraft software must adopt open standards that enable rapid software integration and reuse.

Interoperability with open standards

RTI contributes to all these initiatives, but this focus highlights the open standards that enable software portability and interoperability. At the forefront is the technical standard "Future Airborne Capability Environment (FACE)" from The Open Group. The technical and business approach of FACE addresses these topics through a set of standardized interfaces, operating environments, and business practices. These are essential for ensuring software portability and reusability across flight platforms. Specifically, FACE defines the Transport Services Segment (TSS). It integrates the data flow from sensors, I/O devices, or other nodes and provides a comprehensive, unique, and consistent representation of this data for applications.

The commercial implementation of the FACE Transport Services Segment (TSS) is RTI Connext TSS, a software connectivity framework with two key methods for interoperability:

• Use of open standards for data-centric communication and data transmission over the network.
• Support for the connection of TSS manufacturers via the FACE Transport Protocol Module (TPM) interface.

Open Standards for Data-Centric Communication and Data Transmission

With Connext TSS, both component developers and system integrators can utilize the FACE Technical Standard as well as the Data Distribution Service (DDS) standard. DDS defines an interface for publish-subscribe, request-reply, and RPC communication, offering a loosely coupled, decentralized architecture with peer-to-peer communication for low latency without a single point of failure. No brokers or servers are required. On the wire, DDS uses the Real-Time Publish-Subscribe (RTPS) network protocol, enabling an ecosystem of implementations that communicate seamlessly thanks to open, widely adopted standards.

Cross-vendor TSS integration via the FACE-TPM interface

A specific challenge associated with the FACE TSS is that FACE leaves the choice of network protocol up to the software provider. This means that competing TSS solutions are not compatible with one another due to their design. Ultimately, FACE developed the Transport Protocol Module (TPM), an additional software module required for interoperability between TSS. At the time this article was written, no two providers had demonstrated a successful integration between their TSS and TPMs. In fact, RTI led the Modular Open Systems Approach (MOSA) Risk Reduction Sub Task 1 (Task 3) under Advanced Technology International, which specifically aimed to evaluate the maturity of the TPM standard for this purpose.

FACE-TPM Vision Becomes Reality

In April this year, a cross-vendor and protocol-agnostic integration solution was presented in collaboration with On-Line Applications Research (OAR), highlighting the design differences between TSS and TPM implementations. This demonstration significantly reduces the risk for complex FACE programs, whose designs must be future-proof for platform upgrades or modernizations based on different network protocols.

It becomes clear that the implementation of open standards can help make military programs future-proof. Connext TSS leverages the benefits of open standards from the ground up and now offers the additional advantage of a proven, vendor-independent integration solution with FACE TPM. Connext TSS is available with certified FACE 3.1 compliance and COTS DO-178C DAL-A certification, reducing costs and risks for modular, open, and safety-critical avionics systems. (se)

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*Daniel Ryan is Product Manager for Aviation Products at Real-Time Innovations.

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