14 CFR § 27.959 - Unusable fuel supply.

---
identifier: "/us/cfr/t14/s27.959"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 27.959 - Unusable fuel supply."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "27.959"
section_name: "Unusable fuel supply."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "27"
part_name: "AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "49 U.S.C. 106(f), 106(g), 40113, 44701-44702, 44704."
regulatory_source: "Docket No. 5074, 29 FR 15695, Nov. 24, 1964, unless otherwise noted."
cfr_part: "27"
---


# 27.959 Unusable fuel supply.

The unusable fuel supply for each tank must be established as not less than the quantity at which the first evidence of malfunction occurs under the most adverse fuel feed condition occurring under any intended operations and flight maneuvers involving that tank.