Airworthiness Articles

Introduction

An Advisory Circular was issued in February 1977 (AAC 97-1) titled Cabin Materials - Fire Hazard, which provided advice on a simplified test to show compliance with the flammability rules of materials used in small aircraft cabins.

However, owing to concern that the 1977 material contains inappropriate advice, and considering the availability of more appropriate test facilities, AAC 97-1 is hereby cancelled and the procedures described in AAC97-1 should not be used to demonstrate compliance.

Background

All materials used in an aircraft cabin must meet the applicable flammability requirements for that aircraft type. Such materials include carpet, seat upholstery, curtains and decorative furnishings.

Whether you are designing an aircraft or repairing or replacing the interior material in an existing aircraft, you will need to understand and show compliance with the applicable material flammability requirements.

This circular is written to provide guidance on the requirements for different aircraft, to describe what is involved in showing compliance and to highlight some concerns and potential problems. The organisation carrying out the repair or refurbishment and signing for completion of the work is responsible to ensure compliance with the appropriate standards for the particular aircraft. This circular is written as an aid to implement those requirements.

A companion circular will address appropriate procedures for an organisation to demonstrate compliance.

Cabin material in aircraft must meet the required flammability standard. There are three ways to ensure this:

1. carry out all replacement or repairs in accordance with approved data (eg aircraft manufacturer's instructions),
2. obtain material which has been tested to the appropriate standard from an approved supplier, or
3. carry out the appropriate flammability test.

Option 1 is the preferred and easiest as it is then the responsibility of the supplier of that data to show compliance. If you stick to approved data you do not need to worry about the rest of this circular.

Requirements

The requirements for flammability of aircraft interior materials can be separated into two groups:

Large Transport Category Aircraft (typically FAR 25) and small aircraft (typically FAR 23). Helicopters come under different rules (FAR 29 and FAR 27 respectively) where the division is essentially the same. It should be noted that at the crossover point, the large FAR 23 aircraft used in the "commuter" role, many of the requirements are the same as for FAR 25 (Transport) aircraft.

Unless specific retrospective action has been required, the appropriate basis for any modification or repair to an aircraft is the relevant standard stated in the type certification basis. To ensure that the correct requirement is used, the Certification Basis for the aircraft type should be checked.

1. Transport Category Aircraft (FAR 25) Rules

Specific retrospective requirements in Transport category aircraft have been introduced over the last 10 years which significantly improve the flammability of cabin materials. These address specific tests for specific critical areas of the cabin in addition to the general "vertical burn test" for all cabin materials. The specific tests include: (1) oil burner tests for seat cushions (AD/GEN/63); (2) radiant heat release and smoke criteria for interior ceiling and side-wall panels (AD/GEN/68); and (3) burn-through criteria for cargo compartment liners (AD/GEN/70).

The details of these tests are covered in existing documentation (see FAR 25.853, FAR 25 Appendix F and FAA Report DOT/FAA/CT-85/15 "Aircraft Material Fire Test Handbook"). For further information please contact your local CASA Office.

2. Small Aircraft Rules

2.1 Requirements for Interior Materials in Small Aircraft ie FAR 23 in the Normal, Utility and Aerobatic categories BUT NOT commuter category.

Note 1: For earlier aeroplanes, the previous standards (eg CAR 3) have similar requirements.

Note 2: FAR 23 Commuter Category is a specific Design Standard category for the aircraft. This should not be confused with the often used Australian term commuter category or commuter operations when used in a general sense referring to any aircraft in low capacity RPT operation.

FAR 23.853 (a) The materials (for each compartment to be used by the crew or passengers) must be at least flame resistant.

2.1.1 Availability of Approved Materials

Materials complying with the flammability requirements are available from approved aircraft suppliers. These will be accompanied by appropriate documentation. This should be the preferred option as, although other materials can be approved, the required testing, described below, will be avoided. Refer to the companion AAC for CAR 35/36 approvals.

2.1.2 Test of Local Materials

"Flame Resistant" is defined as not susceptible to combustion to the point of propagating a flame, beyond safe limits, after the ignition source is removed (FAR 1).

Local materials may be approved provided the appropriate flammability requirements have been shown to be satisfied by tests. Each batch must be tested and tagged to maintain its identity with the test.

FAA Advisory Circular AC 23-2 describes the test procedures for showing compliance.

This is a horizontal burn test with a 10mm (3/8 inch) gas Bunsen burner on three test specimens 114mm x 317mm (approx. 41/2 inches x 12-1/2 inches). Refer to FAA AC 23-2 for full details.

These tests need to be conducted under controlled laboratory conditions by a competent organisation.

2.2 For FAR 23 Commuter Category Aircraft

FAR 23.853(d) addresses the additional requirements for the cabin materials in commuter category aircraft. These basically require a vertical burn test (with different performance criteria for different cabin items) as against a horizontal burn test for other than commuter category small aeroplanes. FAR 23.853(d) and the accompanying FAR 23 Appendix F provide the required test methods. The FAA Aircraft Material Fire Test Handbook referred to in paragraph 1 above also provides information on the vertical burn test.

2.3 For Small Helicopters (FAR 27)

All materials must be at least "flash resistant". Walls and ceiling linings, and the covering of upholstery, floors, furnishings must be at least "flame resistant"

Flash Resistant is defined (FAR 1) as not susceptible to burning violently when ignited. Flash resistant material must also meet horizontal burn test criteria (see paragraph 2.1 above for small aeroplanes) except with different performance measures. FAA AC 23-2 provides details of these.

3. Use of Fire Retardants - Warning

If fire retardant chemicals are used to provide the required flammability properties of the material, the long term performance of the treated material must be taken into consideration to ensure the material in service continues to meet the certification standard.

This fire retardant performance is known to deteriorate with wear and, particularly, cleaning. Therefore, the service life of material treated with the fire retardant must be established and appropriate maintenance instructions provided to ensure continuing airworthiness of the cabin interior.

An aircraft which has been refurbished with material treated with fire retardant may no longer meet the flammability requirements after time in service. If instructions for reapplication of the retardant have not been established, then the effectiveness must be suspect.

 

Attachment: AC23-2 FAA Flamability Standards.pdf 

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