---
title: "CS 25.959 Unusable fuel supply — CS-25 · Avioverse"
description: "The unusable fuel quantity for each fuel tank and its fuel system components must be established at not less than the quantity at which the first…"
url: "https://avioverse.aero/regulations/easa/cs-25/subpart-e/cs-25-959"
---

# CS 25.959 Unusable fuel supply

Large Aeroplanes (CS-25) · CS-25 · EAR revision 26 Jan 2023

IR Implementing rule

## CS 25.959 Unusable fuel supply

The unusable fuel quantity for each fuel tank and its fuel system components must be established at not less than the quantity at which the first evidence of engine malfunction occurs under the most adverse fuel feed condition for all intended operations and flight manoeuvres involving fuel feeding from that tank. Fuel system component failures need not be considered.

IR · CS 25.959 — CS-25 · ED Decision 2003/2/RM · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

[All rules in SUBPART E – POWERPLANT](https://avioverse.aero/regulations/easa/cs-25/subpart-e)

Consolidated from the EASA Easy Access Rules (revision 26 Jan 2023, extracted 13 Oct 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.