DO-178B, Software Considerations in Airborne Systems and Equipment Certification is a document dealing with the safety of software used in airborne systems.

The FAA

Federal Aviation Administration

The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 applies DO-178B as the document it uses for guidance to determine if the software will perform reliably in an airborne environment, when specified by the Technical Standard Order (TSO) for which certification is sought.

It was published by RTCA, Incorporated, and development was a joint effort with EUROCAE who publish the document as ED-12B.
The Design Assurance Level (DAL) is determined from the safety assessment process

ARP4761

ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment is a standard from the Society of Automotive Engineers . In conjunction with SAE ARP4754, ARP4761 is used to demonstrate compliance with 14 CFR 25.1309 in the U.S...

 and hazard analysis

Hazard analysis

A hazard analysis is used as the first step in a process used to assess risk. The result of a hazard analysis is the identification of risks. Preliminary risk levels can be provided in the hazard analysis. The validation, more precise prediction and acceptance of risk is determined in the Risk...

 by examining the effects of a failure condition in the system.