OPEN IS AN INTERFACE, NOT A LABEL

Written by Colby Hall

What the military learned about modular design in 2026, and what it means for the aircraft cabin.

Two years ago we wrote that modularity is the future of aerospace engineering. MOSAIC itself was inspired by the military's Modular Open Systems Approach, or MOSA. This year the defense world has had a very public conversation about what modular actually takes. The answer is less about boxes and more about the lines between them.

Modular is now the law, and the bar is rising

MOSA has been written into U.S. law since 2019. Under 10 U.S.C. § 4401, major defense programs must be built around modular components and open, consensus-based interfaces wherever practicable. That covers a lot of hardware: major programs account for roughly $99.6 billion of the FY2026 defense request.

The services are now tightening what "compliant" means. In August, the Navy said it is setting baseline expectations for how every program applies MOSA, and that industry is responding with module-level products. In September, the Department of War described a new cadre of MOSA experts embedded with weapons programs, with MOSA measures used to judge program health.

Three lessons worth borrowing

1. Saying "open" is not being open. The department's message at this fall's MOSA summit was blunt: a system is open only when its standard interfaces are actually implemented, tested and reused across programs. A proprietary implementation of an open standard does not count.

2. Protect the module, open the seam. Vendors can keep their intellectual property inside the box. What must stay open is the interface that lets someone connect, test or replace that box. Under MOSA, the government asks for technical data on the interface, not the module's internal design. That bargain lets a small company compete for one module without competing for the whole system.

3. Write it into the contract, not just the brochure. Panelists at the same summit said many solicitations ask for MOSA without saying what they expect delivered. Their fix: carry open-architecture requirements into the interface, data-rights, sustainment and evaluation sections, and tie them to a planned upgrade.

Why this matters in the cabin

VIP and business aviation cabins have the same problem on a smaller scale. A cabin is a stack of subsystems from different vendors: lighting, audio, video, connectivity and cabin management. Too often they talk over closed buses and proprietary command sets that need special tools to troubleshoot. When one piece ages out, the refit touches everything around it.

MOSAIC applies the military's lessons directly:

  • Open seams, private modules. Commands one system uses to talk to another are published openly to the MOSAIC repository. What happens inside a vendor's subsystem can stay proprietary, as long as the tools to troubleshoot it are available.

  • Common, testable interfaces. Standard Ethernet, a VLAN for each ATA chapter, and open protocols such as AES67 for audio. A mechanic can test the network with ordinary tools instead of a vendor laptop.

  • Use what fits. MOSAIC is a framework, not a monolith. A lighting refit can adopt the lighting sections without forcing a new audio system.

Three questions for your next cabin program

Before you sign for a cabin system, ask three things. What is the interface? Who publishes it? Could another vendor's box plug into it tomorrow? If the answers are vague, the system is not open, whatever the brochure says.

The defense community is learning that modularity is earned at the interface. Cabins can learn it faster. If you build cabin hardware, integrate aircraft or certify them, join the MOSAIC working group at info@mosaic-aero.com.

Sources

Colby Hall
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MOSAIC, A FRAMEWORK FOR THE FUTURE