StacksVerified U.S. regulatory reference

14 CFR §25.1553

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
If the unusable fuel supply for any tank exceeds one gallon, or five percent of the tank capacity, whichever is greater, a red arc must be marked on its indicator extending from the calibrated zero reading to the lowest reading obtainable in level flight.