Avionics software is embedded software with legally-mandated safety and reliability concerns used in avionics. The main difference between avionic software and conventional embedded software is that the development process is required by law and is optimized for safety.

Interestingly, some claim that the process described below is only slightly slower and more costly (perhaps 15 percent) than the normal ad-hoc processes used for commercial software. Since most software fails because of mistakes, eliminating the mistakes at the earliest possible step is also a relatively inexpensive, reliable way to produce software. In some projects, however, mistakes in the specifications may not be detected until deployment. At that point, they can be very expensive to fix.

The basic idea of any software development model is that each step of the design process has outputs called "deliverables." If the deliverables are tested for correctness and fixed, then normal human mistakes can't easily grow into dangerous or expensive problems. Most manufacturers follow the waterfall model to coordinate the design product, but almost all explicitly permit earlier work to be revised. The result is more often closer to a spiral model.

For an overview of embedded software see embedded system and software development models. The rest of this article assumes familiarity with that information, and discusses differences from commercial embedded systems and commercial development models.