Discusión

Over the life of aeronautical products, defects affecting airworthiness are discovered. These result from design conditions not foreseen in the original Product Certification or manufacturing deficiencies. Many become evident only after years of in-service operation and are completely unforeseen. Structural fatigue or corrosion are examples. FAR/JAR 39 forms the basis of the procedures.

Definition

The Airworthiness Directive (AD) system is the medium for correction for any condition that causes the product to be out of conformity to the Approved Design Standards. An AD identifies the disparity, defines its particulars, and establishes limitations for inspection, repair, or alteration under which the product may continue to be operated. They are issued by the National Aviation Authority from either the manufacturer’s or the airline’s country.

Airworthiness Directives effectively alter the original certification of the product. Thus, for example an AD against a Type Certificated product becomes a part of the Type Certificate.

The Airworthiness Directives may also be raised due to change in aviation legislations e.g.

mandating of TCAS and EGPWS.

Distribution They are distributed

i) telegraphically to owners and operators ii) Organisations such as IATA, ATA etc.

iii) Foreign Airworthiness Authorities Their availability can be checked through

i) FAA ‘Summary of Airworthiness Directives’

ii) CAA (UK) ‘Mandatory Aircraft Modification and Inspection Summary (MAMIS)’

iii) CAA (UK) ‘Foreign Airworthiness Directives’

These summaries are used to check any outstanding ADs against a given type of design and hence the airline and the operator would not be excused for missing any ADs.

Contents of an Airworthiness Directive

Generally the Airworthiness Directive is made up of several parts:

i) AD title ii) Applicability

iii) Required compliance action iv) Effective dates

v) Compliance time We will proceed to detail the contents

Applicability of ADs

An AD contains an applicability statement specifying the product to which it applies. It applies to the make and model set forth in this statement, regardless of the classification of the product or category of the Airworthiness Certificate issued for an aircraft. it applies to each product identified in the statement, regardless of whether it has been modified, altered, or repaired in the subject areas. The presence of any alteration or repair does not remove the product from applicability.

Type Certificate and Airworthiness Certification information is used to identify the product affected. Applicability may be defined by specifying serial numbers or manufacturer's line numbers, part numbers, or other identification. When there is no reference to serial numbers, all serial numbers are affected.

Effective dates

The effective date of the AD or an amendment is be found in the last sentence of the body of each AD. For example, "This amendment becomes effective on July 10, 1995." Similarly, the revision date for an emergency AD distributed by telegram or priority mail is the date it was issued. For example, "Priority Letter AD 95-11-09, issued May 25, 1995, becomes effective upon receipt." The "clock" tracking compliance starts with the effective date.

Compliance time

Compliance with an AD is mandatory. No person may operate' a product to which an AD applies, except in accordance with the conditions of the AD. An airplane that has not had an effective AD accomplished within specified limits is out of conformity and is thus not airworthy. This is consistent with the definition of airworthiness discussed before.

Compliance time is stated in various ways. Typical compliance statements include;

"Prior to further flight, inspect..."

"Compliance is required within the next 50 hours time in service after the effective date of this AD..."

'Within the next 10 landings after the effective date of this AD... "

'Within 50 cycles...” to which cycle refers to the complete aircraft / components operating cycles.

"Within 12 months after the effective date of this AD..."

No person may operate an affected product after expiration of the stated compliance time. In some instances, an AD may authorize operation after the compliance date has passed, if a special flight permit is obtained. These are granted only when the AD specifically permits it.

Recurring/periodic ADs

In order to provide for flexibility in administering compliance requirements, an AD should provide for adjustment of repetitive inspection intervals to coincide with inspections required by approved maintenance program inspections. Any conditions and approval requirements under which adjustments may be allowed are stated in the AD. If the AD does not contain such provisions, adjustments are usually not permitted. However, amendment, modification, or adjustment of the terms of the AD may be requested.

Alternative or equivalent means of compliance

Many ADs indicate the acceptability of one or more alternative methods of compliance. Any alternative method of compliance or adjustment of compliance time other than that listed in the AD must be substantiated to and approved by the certifying Airworthiness Authority before it may be used.

The alternative method may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition.

It may be stated in the AD itself e.g. an extra repetitive inspection in place of a mandatory modification.

Reference to Manufacturer's Service Bulletins in ADs

Manufacturer's Service Bulletins are normally not related to airworthiness. Incorporation of them is, therefore, not mandatory. However, when a manufacturer's Service Bulletin is incorporated, by reference, into the Airworthiness Directive accomplishment instructions the bulletin becomes mandatory. Thus any change in the details of the bulletin constitutes alternative means of accomplishment. Changes, therefore, must be approved.

DEFERRED MAINTANENCE MEL / CDL