Zonal safety analysis

Zonal Safety Analysis (ZSA) is one of three analytical methods which, taken together, form a Common Cause Analysis (CCA) in aircraft safety engineering under SAE ARP4761. The other two methods are Particular Risks Analysis (PRA) and Common Mode Analysis (CMA). Aircraft system safety requires the independence of failure conditions for multiple systems. Independent failures, represented by an AND gate in a fault tree analysis, have a low probability of occurring in the same flight. Common causes result in the loss of independence, which dramatically increases probability of failure. CCA and ZSA are used to find and eliminate or mitigate common causes for multiple failures.

ZSA is a method of ensuring that the equipment installations within each zone of an aircraft meet adequate safety standards with respect to design and installation standards, interference between systems, and maintenance errors. In those areas of the aeroplane where multiple systems and components are installed in close proximity, it should be ensured that the zonal analysis would identify any failure or malfunction which by itself is considered sustainable but which could have more serious effects when adversely affecting other adjacent systems or components. [1]

Aircraft manufacturers divide the airframe into zones to support airworthiness regulations, the design process, and to plan and facilitate maintenance. The commonly used aviation standard ATA iSpec 2200, which replaced ATA Spec 100, contains guidelines for determining airplane zones and their numbering. Some manufacturers use ASD S1000D for the same purpose. The zones and subzones generally relate to physical barriers in the aircraft. A typical zone map for a small transport aircraft is shown.

...
Wikipedia