Extended Operations (ETOPS) Significant System

Means an airplane system, including the propulsion system, the failure or malfunctioning of which could adversely affect the safety of an ETOPS flight, or the continued safe flight and landing of an airplane during an ETOPS diversion. Each ETOPS significant system is either an ETOPS group 1 significant system or an ETOPS group 2 significant system.
  1. An ETOPS group 1 Significant System—
    1. Has fail-safe characteristics directly linked to the degree of redundancy provided by the number of engines on the airplane.
    2. Is a system, the failure or malfunction of which could result in an IFSD, loss of thrust control, or other power loss.
    3. Contributes significantly to the safety of an ETOPS diversion by providing additional redundancy for any system power source lost as a result of an inoperative engine.
    4. Is essential for prolonged operation of an airplane at engine inoperative altitudes.
  2. An ETOPS group 2 significant system is an ETOPS significant system that is not an ETOPS group 1 significant system.

Source: 14 CFR Federal Aviation Regulations §1