Definition
An aircraft system whose failure or degradation could adversely affect the safety of an Extended-range Twin-engine Operations (ETOPS) flight, or whose continued proper functioning is important to safe flight and landing during an ETOPS diversion. These systems receive special design, maintenance, and reliability scrutiny because a twin-engine aircraft on an ETOPS route may be hours from the nearest suitable airport.
Plain English
On a long over-water or remote flight in a two-engine aircraft, certain systems are critical because the plane may be far from any airport. An ETOPS Significant System is one of those critical systems, and it gets extra-careful design, maintenance, and monitoring to make sure it stays reliable.
Context Anchor
Seen in airline operations, maintenance, dispatch, and approval rules for ETOPS flights, especially when deciding which airplane systems must meet higher reliability standards.
Derivation
ETOPS stands for Extended-range Twin-engine Operations. The word 'significant' here means 'mattering enough to require special attention' — not just 'important in general,' but specifically singled out for tighter rules.
Why Pilots Care
These systems receive extra reliability checks and maintenance so the aircraft can reach a suitable diversion airport without increased risk.
Analogy
It is like checking the systems on a boat before crossing a wide stretch of water. A small cabin light may not matter much, but the engine, fuel system, and bilge pump matter because losing them could change the whole safety picture.
Intuition Check
Significant does not just mean generally important here. It means the system is important specifically because its failure could affect safety or the ability to keep flying safely to an airport during ETOPS.
Example Sentence 1
Before dispatching the 767 on its transatlantic ETOPS segment, the maintenance crew confirmed every ETOPS Significant System was fully operational.
Example Sentence 2
Mechanics perform additional inspections on all ETOPS significant systems before the aircraft is released for a transoceanic flight.