By Eugene le Roux, FSAIRAC, and Eamonn Ryan
In any complex engineering project, whether it’s building an aircraft, developing a software system, or constructing a new energy grid, one of the most critical – and often underestimated – aspects is the interface. This is Part Two of a three-part series.
Each level of interface comes with its own challenges. Pressfoto | Freepik.com
Interfaces are not confined to one level of a system; they can exist across multiple hierarchical levels:
- Component-level interfaces (for example, between a motor and its controller)
- Subsystem interfaces (for example, between propulsion and avionics in an aircraft)
- System-to-system interfaces (for example, between two aircraft in a formation flying system)
- External interfaces (for example, the system’s interface with users, the environment, or other infrastructure)
Each level of interface comes with its own challenges, and all need to be managed cohesively to prevent integration issues down the line.
Primary versus secondary systems
When multiple systems need to interface with each other, conflicts may arise – especially if the systems were developed independently or follow different standards. In such situations, one common strategy is to designate a ‘primary’ or ‘dominant’ system, whose interface specifications take precedence. The other systems, often referred to as ‘secondary’ or ‘slave’ systems, must adapt to the primary system’s requirements.
While this approach simplifies decision-making, it can lead to expensive redesigns for existing systems. Therefore, the ideal approach is early co-ordination. By ensuring compatibility from the outset, costly retrofits and integration risks can be minimised. This is where interface planning becomes a vital part of system architecture.
The characteristics of good interface requirements
Like all system requirements, interface specifications must be:
- Complete: They should fully describe the interaction without leaving room for ambiguity
- Consistent: No part of the interface spec should contradict other requirements
- Concise: The specification should be clear and not bloated with unnecessary detail
But how can one tell if an interface requirement is complete? A good test is to ask: Could an independent team design this interface without needing further clarification? If the answer is yes, then the requirement is likely complete.
