14 CFR Part 39 Airworthiness Directives
Categories of Airworthiness Directives
Publication of Airworthiness Directives
Construction of an Airworthiness Directive
This part of 14 CFR prescribes airworthiness directives (AD) that apply to aircraft, aircraft engines, propellers, or appliances (hereinafter referred to in this part as “products”) when an unsafe condition exists in a product, and that condition is likely to exist or develop in another product of the same type design.
Airworthiness Directives are Federal Aviation Regulations that are published in the Federal Register as amendments to 14 CFR Part 39. They apply to aircraft, aircraft engines, propellers, or appliances, which are referred to as “products,” and are issued when an unsafe condition is found to exist in a product, and when that condition is likely to exist or develop in another product of the same type design. ADs are published in the following four categories.
An NPRM is issued and published in the Federal Register when an unsafe condition is discovered in a product. Interested persons are invited to comment on the NPRM by submitting such written data, views, or arguments as they may desire. The comment period is usually 60 days, and proposals contained in the notice may be changed or withdrawn in light of the comments received. When an NPRM is adopted as a final rule, it is published in the Federal Register, printed, and distributed by first-class mail to the registered owners of the product affected.
ADs of an urgent nature are adopted without the NPRM process, as immediately adopted rules. These ADs usually become effective less than 30 days after publication in the Federal Register and are distributed to the registered owners of the product affected.
Emergency ADs are issued when immediate corrective action is required. Emergency ADs are distributed to the registered owners of the product affected by telegram, priority mail, or other electronic methods and are effective upon receipt. Emergency ADs are published in the Federal Register as soon as possible after the initial distribution.
ADs may be issued which apply to engines, propellers, or appliances installed on multiple makes or models of aircraft. When the product can be identified as being installed on a specific make or model aircraft, AD distribution is made to the registered owners of those aircraft. However, there are times when a determination cannot be made, and direct distribution to the registered owner is impossible. For this reason, aircraft owners and operators are urged to subscribe to the Summary of Airworthiness Directives which contain all previously published ADs and a biweekly supplemental service. To access AD notes and other regulatory data, you may also use the internet. The most comprehensive site is: www.airweb.FAA.gov/rgl
Individual ADs are distributed to the owners of the affected products and are also made available to maintenance personnel by subscription from the FAA, as described in AC 00-44 Status of the Federal Aviation Regulations.
Printed ADs are published in two volumes, with each volume containing two books:
The Summary of AD Notes contains two indexes; one is alphabetical by the manufacturer of the product, and the other is a numerical listing of all ADs from the oldest to the most recent. The indexes are updated every six months.
New and revised ADs are compiled by the FAA every two weeks and mailed out to the subscribers of the service in the “Biweekly Listings.”
Each AD contains an applicability statement specifying the product (aircraft, aircraft engine, propeller, or appliance) to which it applies. Some aircraft owners and operators mistakenly assume that ADs do not apply to aircraft with other than standard airworthiness certificates, i.e., special airworthiness certificates in the restricted, limited, or experimental category. Unless specifically stated, ADs apply to the make and model set forth in the applicability statement regardless of the classification or category of the airworthiness certificate issued for the aircraft. Type certificate and airworthiness certification information are used to identify the product affected. Limitations may be placed on the applicability by specifying the serial number or number series to which the AD is applicable. When there is no reference to serial numbers, all serial numbers are affected.
Airworthiness Directives are all written to a standard format. All contain the AD number, the amendment number, an applicability statement, a required compliance time or date, the effective date and a compliance statement.
Historically, AD notes were identified by a six-digit number such as 90-08-14. The first two digits (90) identify the year the AD was issued. The second two digits (08) identify the biweekly period in which the AD was issued. This is the fifteenth or sixteenth week of the year. The last two digits (14) is the sequential number of the AD issued during this time period. This was the fourteenth AD issued in the eighth biweekly period. Currently, AD notes are identified by an eight-digit number such as 2004-22-08. This change started with AD notes issued in the year 2000.
If the AD is revised, the letter “R” and the number of revisions will be appended to the AD number. For example, AD 81-23-01 R1 is the first revision to AD 81-23-01. It is not uncommon that a revised AD includes additional maintenance procedures that were not in the original AD. The instructions must be complied with and the revised AD be signed off even though the original AD was a one-time compliance AD.
The letter “T” preceding the AD number means that the AD was telegraphed to the owners/operators of the unsafe aircraft.
AD notes are amendments to 14 CFR Part 39 and, therefore carry amendment numbers. This amendment number is changed when the AD is revised. For example, the amendment number of AD 90-08-14 as shown on Page 4-20 is Amendment 39-6563.
This statement lists the products to which the AD applies. The applicability is given by product model number and applicable serial numbers.
There are a number of ways compliance time may be stated:
Some ADs are repetitive, and must be complied with at specified intervals after the initial compliance. These repetitive compliance requirements may be dispensed with or terminated when a specified permanent fix is developed and complied with.
Near the end of the AD there is a statement similar to the following: “This amendment (39-6563, AD 90‑18-14) becomes effective on May 7, 1990.”
This statement specifies the action that is required by this AD. A typical compliance statement is as follows: “Compliance: Required as indicated in the body of this AD, unless already accomplished.” The body of the AD then describes the action that is required and specifies the method of compliance.
Each AD also includes a short section which indicates that someone in the FAA is authorized to approve “Alternative Methods of Compliance” for this AD. This can be as simple as requesting a variation of the inspection interval, or as complex as fabricating a totally different method for addressing the unsafe condition identified by the AD.