En-route fuel supply: flag and supplemental operations

This regulation sets fuel requirements for Part 121 flag and supplemental operations, with different rules for standard long-range flights versus ETOPS flights.

For turbine aircraft with more than two engines flying more than 90 minutes from an adequate airport, you must carry enough fuel to reach that airport assuming rapid decompression at the worst point, descend safely per oxygen requirements, account for expected winds, then hold 15 minutes at 1,500 feet and land normally.

ETOPS flights have stricter requirements. You must carry enough fuel to reach an ETOPS alternate airport assuming the worst-case scenario (rapid decompression and/or engine failure), plus additional fuel for:

• Wind forecast errors (5% increase)
• Potential icing conditions
• Engine deterioration (5% unless monitored)
• 15-minute hold at 1,500 feet and instrument approach
• APU consumption if required

These requirements ensure adequate fuel reserves when operating far from suitable airports, accounting for multiple potential emergencies and forecast uncertainties.

*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.*