Ensuring that redundant channels are not physically or logically compromised by a single environmental event.
ZSA divides the aircraft into geographic 3D zones (e.g., Zone 110: Nose Radome, Zone 400: Empennage). It inspects whether hydraulic lines, electrical wiring, and flight control cables are routed with sufficient physical clearance to prevent chafing, fire, or fluid spray propagation.
PRA assesses localized catastrophic hazards: uncontained turbine engine rotor burst (throwing high-energy titanium fragments through the cabin), bird strikes on the windshield, tire bursts in the wheel well, and lightning strikes.