Identifying failure conditions and assigning qualitative hazard categories early in aircraft conceptual design.
Every aircraft function (e.g., Maintain Lateral Control, Provide Cabin Pressurization) is evaluated against potential failure conditions: complete loss of function, uncommanded operation, intermittent operation, or erroneous output during critical flight phases (takeoff, landing, high-altitude cruise).
Catastrophic failure conditions (multiple fatalities, hull loss) mandate an allowable probability of less than 10^-9 per flight hour, requiring full architectural independence and DAL A hardware and software development processes.