---
title: "CS 25.1326 Flight instrument external probes heating systems alert — CS-25 · Avioverse"
description: "(See AMC 25.1326) If a flight instrument external probe heating system is installed, an alert must be provided to the flight crew when the flight…"
url: "https://avioverse.aero/regulations/easa/cs-25/subpart-f/cs-25-1326"
---

# CS 25.1326 Flight instrument external probes heating systems alert

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

IR Implementing rule

## CS 25.1326 Flight instrument external probes heating systems alert

(See AMC 25.1326)

If a flight instrument external probe heating system is installed, an alert must be provided to the flight crew when the flight instrument external probe heating system is not operating or not functioning normally. The alert must comply with the following requirements:

(a) The alert provided must conform to the Caution alert indications.

(b) The alert provided must be triggered if either of the following conditions exists:

(1) The flight instrument external probe heating system is switched ‘off’.

(2) The flight instrument external probe heating system is switched ‘on’ and is not functioning normally.

\[Amdt 25/16]

IR · CS 25.1326 — CS-25 · ED Decision 2015/008/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

AMC Acceptable means of compliance

## AMC 25.1326 Flight instrument external probes heating systems alert

CS 25.1326 requires that if a flight instrument external probe heating system is installed, an alert must be provided to the flight crew when the flight instrument external probes heating system is not operating or not functioning normally.

It is expected that probe heating system failures are indicated to the flight crew if such failures have an impact on the performance of the heating system to the extent of having an “effect on operational capability or safety” (see CS 25.1309).

In accordance with CS 25.1309(c) and CS 25.1322(b), a Caution category of alert is required by CS 25.1326 for immediate crew awareness and subsequent crew action.

It should be assumed that icing conditions exist during the failure event. The decision to provide heating system failure indication should not be based on the numerical probability of the failure event. If the failure could potentially have hazardous or catastrophic consequences, then this failure must be indicated.

The reliability of the system performing the probe heating system failure detection and alerting should be consistent with the safety effect induced by the failure. Refer to AMC 25.1309, chapter 9(c) for more detailed guidance.

\[Amdt No: 25/16]

AMC · AMC 25.1326 — CS-25 · ED Decision 2015/008/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

[All rules in SUBPART F – EQUIPMENT](https://avioverse.aero/regulations/easa/cs-25/subpart-f)

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.