ADs are issued when the aviation authority -usually manufacturer aviation authority - finds that an unsafe condition exists in a product (aircraft, aircraft engine, propeller, or appliance.)
These AD's notify aircraft owners and operators of potentially unsafe conditions and require special inspections, repairs, or alterations to correct the unsafe condition.
Types of Airworthiness Directives (ADs) according to FAA:
- Notice of Proposed Rulemaking (NPRM):
After an unsafe condition is discovered, a proposed solution is published as an NPRM, which solicits public comment on the proposed action. Request for Comments. 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.NPRM link
- Final Rule:
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 a response to the substantive comments or state there were no comments received.
Final Rule Link
- Emergency Airworthiness Directives EADs:
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. For more information, see the Emergency AD page.
- Superseded AD:
An AD is considered no longer in effect when it is superseded by a new AD. The superseding AD identifies the AD that is no longer in effect. There are no compliance requirements for an AD that has been superseded.
Types of Airworthiness Directives (ADs) according to EASA:
- Sensitive Security Airworthiness Directive (SSAD):
An SSAD is an AD issued or adopted by EASA that mandates certain corrective actions, the content of which includes security-sensitive information. An SSAD will be disseminated by EASA to those states having affected aircraft on the register. Further distribution of the SSAD to operators of the affected aircraft or other concerned parties remains under the State of Registry responsibility and should be done on a "need to know" basis only. An SSAD record is uploaded in the EASA Safety Publications publishing tool, but only after the end of the SSAD compliance time and without attachments;
- Mandatory Continuing Airworthiness Information MCAI:
The EASA Safety Publications publishing tool (SP Tool) offers a complete list of Airworthiness Directives that have been issued or approved by EASA since 28/09/2003. The tool also contains all Proposed Airworthiness Directives (PAD) and allows users to submit their comments during the consultation period. After 15/09/2008, new Safety Information Bulletins, Foreign State of Design Safety Publications and Foreign State of Design ADs are published within the EASA SP tool. From July 2016, the EASA SP tool also includes Conflict Zone Information Bulletins (CZIB). The subscription service for new publications enables users to define their own filter and to receive notifications for these filtered documents.
Please consult the user guide for information on how to view and filter new publications and on how to subscribe to their automatic notification
From September 2016, the Safety Publications Tool has been changed to include a new taxonomy for Parts and Appliances ADs – click here for details.
Not all the ADs issued by the NAAs prior to 28/09/2003 (start date of the Agency) are included at this time. Any State of Design AD not (yet) located in the EASA SP Tool should be retrieved from the original State of Design National Airworthiness Authority (NAA), likely available on the respective NAA websites.
SB are noticing to aircraft operators from a manufacturer notifying them of product improvement.
Having realized that there were distinct levels of seriousness to a service bulletin, manufacturers started to categorize them as optional, recommended, alert, mandatory, informational, etc. It was left to the manufacturers to classify a service bulletin as they considered best for there was no standard for the terminology. Differentiation between non-mandatory service bulletins is done and decided only by the authority (FAA - EASA).
Types of Service Bulletins:
Mandatory Service Bulletins :
Through the DOA (Design Organization Approval) oversight process, the Agency promotes that TC/STC holders designate a Service Bulletin (SB) as mandatory only if it is known to them that this SB will also be covered by an AD.
- Alert Service Bulletins :
are issued by the manufacturer when a condition exists that the manufacturer feels is a safety-related item as opposed to just a product improvement. These SB's usually result in the FAA /EASA issuing an AD. The AD will reference the alert service bulletin as a method of compliance with the airworthiness directive.
- Service Information Directive (SID) :
Serviced documents that have been determined by the manufacturer to be of value to an owner/operator in the use of a product by enhancing safety, maintenance or economy.
- Service Information Letters (SIL) :
This category includes all information that may be of use to the owner, operator or maintainer of the aircraft.
If a service bulletin is not an alert service bulletin or a bulletin referenced in an AD, it becomes optional and may or may not be incorporated by the operator.
if you want to know more about service bulletin, types, categories ...etc, you can read the post: All About Service Bulletin SB