ABSTRACT
This chapter defines user-modifiable software (UMS) and provides several examples of such software. It explains certification guidance to consider when designing an airborne system that contains UMS. There are various forms of UMS, including executable source code, aircraft-specific parameter settings, or databases UMS is normally designed and initially approved as part of an airborne system that has both nonmodifiable software and modifiable software. The UMS, on the other hand, is designed to be changed by the user utilizing approved procedures. The type and volume of UMS varies from aircraft to aircraft and airline to airline. Systems with UMS must be designed to be modifiable. Once the software is approved under the type certificate as UMS, it is the user's responsibility to manage the UMS. The available guidance for modifying and maintaining UMS is very sparse; therefore, this section provides some recommendations for users who are required to manage UMS.
