Considering time-limited systems in planning ETOPS alternates

When planning ETOPS flights, you must ensure alternate airports are reachable before critical time-limited systems expire. These systems have finite operating times once activated (like cargo fire suppression bottles).

For ETOPS up to 180 minutes: The alternate must be reachable within the most limiting system's approved time minus 15 minutes, calculated at one-engine-inoperative cruise speed in still air.

For ETOPS beyond 180 minutes: Two conditions apply:

• At all-engines speed (corrected for actual winds/temperature), you must reach the alternate before fire suppression time expires minus 15 minutes
• At one-engine speed (corrected for conditions), you must reach it before any other time-limited ETOPS system expires

This ensures that if a critical system activates (like a cargo fire suppression system discharging), you can reach your alternate airport before the system's protection runs out, maintaining safety margins throughout the diversion.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*