Definition

Airworthiness Directive (AD). A regulatory document which identifies aeronautical products in which an unsafe condition exists, and where the unsafe condition is likely to exist or develop in other aeronautical products of the same type design. It prescribes mandatory corrective actions to be taken, or the conditions or limitations under which the aeronautical products may continue to be operated. The AD is the  common form of mandatory continuing airworthiness information mentioned in Annex 8.

Source: ICAO Doc 9760 - Airworthiness Manual

Description

ADs form part of the ongoing obligations of aircraft certification authorities under Part-21 with regard to the continuing airworthiness of aircraft. They address recommendations for improvements or corrective actions to be implemented by the holder of the Certificate of Airworthiness. The issue of an AD has the effect of making such recommendations mandatory.

The ADs contain mandatory instructions to carry out work on an aircraft, engine, propeller, or component to address an unsafe condition which exists, or is likely to exist, or could develop. It may be issued by any National Aviation Authority (NAA) which has responsibility for the regulation of design of those aircraft or components. It is usual for an NAA to require compliance with an AD issued by another NAA with such responsibility where such aircraft are operated by or maintained by regulated organisations within its jurisdiction.

European Approach

In Europe, ADs are issued by the EASA, acting in accordance with Regulation 2018/1139 on behalf of the European Community, its Member States and of the European third countries that participate in the activities of EASA under Article 66 of that Regulation. The criteria for issuance of an AD are defined in 21A.3B and associated AMC material.

For products, parts, and appliances, for which the Agency only exercises the design responsibilities of the State of Registry, its policy is to endorse automatically the airworthiness directives issued by the State of Design, except if it itself issues a different airworthiness directive before the date that the AD of the State of design takes effect.

EASA can adopt ADs from countries outside the coverage of the EASA Regulation arrangements. Any AD issued by the State of Design for an aircraft imported from a third country, or for an engine, propeller, part, or appliance imported from a third country and installed on an aircraft registered in a EU Member State, shall apply unless EASA has issued a different decision before the date of entry into force of that AD.

Applicable European Legislation

In accordance with Regulation EC 2042/2003 Annex I, Part M.A.301, the continuing airworthiness of an aircraft shall be ensured by accomplishing any applicable ADs. Consequently, no person may operate an aircraft to which an AD applies, except in accordance with the requirements of that AD unless otherwise specified by the EASA [EC 2042/2003 Annex I, Part M.A.303] or agreed with the Authority of the State of Registry [EU 2018/1139, Article 71 exemption].

ADs applicable to an EASA-approved type certificate are those ADs which have been issued or adopted by EASA.

The dissemination of airworthiness directives to aircraft owners is a responsibility of the State of Registry and does not belong to the Agency.

EASA publishes a complete list of ADs that have been issued by EASA or have received an EASA approval number since 28 September 2003. The EASA publication also contains all Proposed Airworthiness Directives (PAD) and allows for user comments for consultation purposes.

After 15th of September 2008, new Safety Information Bulletins, Foreign State of Design Safety Publications and Foreign State of Design ADs are published.

U.S. Process

In the United States, the Federal Aviation Administration (FAA) has the authority and responsibility for the development and issuance of ADs, as defined in FAA Order 8040.1. An AD is a legally enforceable rule issued to correct an unsafe condition in a product, which the U.S. Code of Federal Regulations (14 CFR part 39) defines as an aircraft, aircraft engine, propeller, or appliance. ADs are issued when an unsafe condition exists in a product and the condition is likely to exist or develop in other products of the same type design.

When an unsafe condition exists, the directorate -- Transport Aircraft, Small Airplane, Rotorcraft or Engine and Propeller -- within FAA responsible for the product will draft, coordinate, and issue ADs based on information provided by one of the 12 Aircraft Certification Offices or the Directorate Standards staff.

The standard AD process is to issue a Notice of Proposed Rulemaking (NPRM) followed by a Final Rule. After an unsafe condition is discovered, a proposed solution is published in the Federal Register as an NPRM, which solicits public comment on the proposed action. After the comment period closes, the final rule is prepared, taking into account all substantive comments received, with the rule perhaps being changed as warranted by the comments. The preamble to the final rule AD will provide response to the substantive comments or state there were no comments received.

In certain cases, the critical nature of an unsafe condition may warrant the immediate adoption of a rule without prior notice and solicitation of comments. This is an exception to the standard process. If time by which the terminating action must be accomplished is too short to allow for public comment (that is, less than 60 days), then a finding of impracticability is justified for the terminating action, and it can be issued as an immediately adopted rule. The immediately adopted rule will be published in the Federal Register with a request for comments. The Final Rule AD may be changed later if substantive comments are received.

An Emergency AD is issued when an unsafe condition exists that requires immediate action by an owner/operator. The intent of an Emergency AD is to rapidly correct an urgent safety of flight situation. An Emergency AD may be distributed by facsimile, letter, or other methods. It is issued and effective to only the people who actually receive it. This is known as “actual notice.”

ADs specify inspections that must be carried out, conditions and limitations that must be complied with, and any actions that must be taken to resolve an unsafe condition. Different approaches or techniques that are not specified in an AD can, after FAA approval, be used to correct an unsafe condition. This is known as alternative method of compliance. Although the alternative may not have been known at the time the AD was issued, an alternative method could be acceptable to accomplish the intent of the AD. A compliance time that differs from the requirements of the AD can also be approved if the revised time period provides an acceptable level of safety that is at least equivalent to that of the requirements of the AD.

Operating a product that does not meet the requirements of an applicable AD is a violation of 14 CFR part 39. Operating an aircraft or product that does meet the requirements of an AD is a violation each time it occurs.

The Federal Register is the official daily publication of the U.S. government and is the printed method of informing the public of laws that are enacted or will be enacted. Electronic versions of ADs are available from the Federal Register and from the FAA Regulatory and Guidance Library.

Further Reading

• Further information on Airworthiness Directives may be found on the EASA website
• Airworthiness Directives issued by FAA
• AAIB Safety Study - 1/2016: Airworthiness of Aircraft Registered Overseas and Resident in the UK, published January 2016.
• FAA Order 8040.1C Airworthiness Directives, 3 Oct. 2007.