Airworthiness Directive (AD) Control | Soma Newsletter 2022
Published by: Holymar Ruiz - - September 1, 2021

To effectively control or carry out an AD, there are terms of which we must know their nature, meaning, and/or purpose.

The first thing to know is that a directive is issued to address an unsafe condition in the aircraft or other aeronautical product that compromises airworthiness, and failure to comply with it incurs a violation of the standard. We usually will have two types of these:

– Emergency ADs

– ADs for final actions or Final Rule.

These concepts help us to understand the reason for the AD and even understand why there are ADs to be complied with before further flight (literally immediate or you do not fly unless you have a special permit) and ADs with a threshold that allow the operator to stop the aircraft to comply with the Directive.

Another essential point is that an AD will mainly be supported for its maintenance actions by an SB (Service Bulletin).

In addition, we must know that the applicability of an AD will be even to products that are not airworthy, such as components (appliances) in stock, workshop, shop, etc. Therefore, we must be careful with the control of AD that affects LRU since we must avoid incorporating them into the fleet mainly when the action of the AD is the disincorporation of the equipment or monetary investment in its configuration or maintenance that could lead to additional and unnecessary expenses to the organization.

Now, I will detail specific terms that we must necessarily know and are standard in the industry even when dealing with different authorities such as FAA and EASA:

WOF – whichever occurs first: this term is associated with the compliance interval of the AD when it has more than one, and the interval that is met first in the product must be met example:

.- WOL – whichever occurs later (lo que ocurra después): este término esta asociado al intervalo de cumplimiento del AD cuando tiene más de uno y debe cumplir el intervalo que más tarde en alcanzar el producto, ejemplo:

Effective Date: date to be taken as the starting point for compliance with the AD in the product. The application of an AD is not closed only to the effective date, there are several cases, others common for example mainly when the AD affects a component in which the effectiveness will depend on the TSN / CSN of that product or those AD that are tied to the life time of the airframe, another common case is to depend on the compliance instructions that are dictated in the associated SB.


For example, we see in the image a print AD FAA with application instructions in one of its paragraphs, for example, paragraph (g)(1) from the effective date of the directive (there are cases that an AD refers to be effective from another, we must be attentive to these details).

States of the AD: The directive can have 6 states

– Open: Published AD that has not been fulfilled in the aeronautical product usually within the threshold set by the authority to be performed.

– Repetitive: AD with established recurrence intervals.

– Closed (close): with final action completed.

– Not applicable (N/A): After passing through open status, it undergoes an applicability analysis to support this status.

– Superseded: AD substituted or replaced by a more recent AD that will guarantee an adequate operational safety of the affected product; the superseded AD is no longer valid and usually passes to this status when a new AD is more restrictive in compliance procedures, application times, etc.

– Canceled: AD removed from the publications.

Revision of an AD: in this case, the AD keeps the exact number, but Rn is added where n is the number of times as many revisions have been made; this is done when the change of the AD is of wording, requirements, reduction of applicability, but does not influence in terms of application for compliance. Example:

AD numbering pattern: Here is how the AD number of the two most known authorities is composed:

FAA format may look very much like a date, but it is a location on the calendar and is denoted as follows:

On the other hand, EASA AD numbering is more summarized, for example:

So after reviewing standard terms for an AD control, we could visualize the items we will find in an AD Status Report or Airworthiness Directive Status Control of an aeronautical product.

From the above image, we could find in the industry many different formats; the one shown for the example is a proposed form of aeronautical software called SOMA Software. The important thing is the content and that we know how to interpret any report we come across when reviewing an aircraft or other aeronautical product. In addition, if you are responsible for updating the report when incorporating a new AD, it is vital that it is detailed in compliance with the standard and your local regulation. I recommend reading the 14 CFR Part 39, the AC 39-7D, and your local regulation AD section to familiarize yourself with the items required to correctly control Airworthiness Directives.

With this, I close my post hoping to have contributed a little bit of the extensive world of Airworthiness Directives control to our community.


Holymar Ruiz M.

Project Implementation Manager

Team Member SOMA Software

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