This action establishes United States Area Navigation (RNAV) Route T-581 in the vicinity of Missoula, Montana. FAA-2025-3288 in the Federal Register (90 FR 57721; December 12, 2025), proposing to establish United States Area Navigation (RNAV) Route T-581 in the vicinity of Missoula, Montana. This document amends the current version of that order, FAA Order JO 7400.11K, dated August 4, 2025, and effective September 15, 2025. The RuleThe FAA is amending 14 CFR part 71 by establishing RNAV Route T-581 in the vicinity of Missoula, Montana. T-581: As a new RNAV route, T-581 extends between the Missoula, MT, VOR/DME and the Kalispell, MT, VOR/DME.