Aviation Airworthiness and Maintenance Regulations

Posted on Jun 18, 2025 in Other subjects

Airworthiness Directives (ADs)

An Airworthiness Directive is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics, or other system exists and must be corrected.

They are issued by the National Aviation Authority (NAA) of the country of aircraft manufacturer or of aircraft registration. ADs are mandatory in most jurisdictions and often contain dates or flying hours by which compliance must be completed.

Required Information in ADs

Airworthiness Directives must contain at least the following information:

  1. A specification of the unsafe situation.
  2. A specification of the affected aircraft.
  3. The measures required.
  4. The deadline for the adoption of the required measures.
  5. The date of entry into force.

The purpose of an AD is to notify aircraft owners that the aircraft may have an unsafe condition, may not be in conformity with its certification basis, or other conditions that affect airworthiness. Mandatory actions must be carried out to ensure continued safe operation. In urgent cases, the aircraft must not be flown until a corrective action plan is implemented.

ADs are issued by authorities such as EASA, FAA, Directorate General of Civil Aviation (India), Transport Canada, and Civil Aviation Safety Authority (Australia).

Service Bulletins (SBs)

Service Bulletins (SBs) or technical bulletins are reports issued by manufacturers with updates, modifications, and improvements to defects detected in the aircraft by service centers, by the factory itself, or reported by an aircraft operator. They report model defects and their solutions (e.g., repair kits). The customer may exercise their discretion whether or not to incorporate the bulletins. Sometimes SBs can be mandated by relevant ADs.

SB Content Structure

An SB must contain a title, chapter name keyword, and a brief statement of the work involved. This information must be stated in sequence.

The body of the SB may be preceded by a summary that provides an overview of the information contained in the SB. The body must be prepared in the following sections: planning information, material information, accomplishment instructions, and optional appendices.

SB Recommendations

SBs must include one of these recommendations:

  • SB must be accomplished.
  • Recommended to be accomplished.
  • To introduce improvements.
  • For convenience or option.

Types of Service Bulletins

There are several types of SBs:

  • Alert SB: Requires the urgent attention of the operator and is generally limited to items affecting safety. In some cases, it may be transmitted by telephone.
  • Standard SB: Used when an Alert SB is not required.
  • Engine Conversion SB: Contains information necessary to convert engine models from one designation level to another.

Minimum Equipment List (MEL)

The Minimum Equipment List (MEL) is a document that lists the equipment that may be temporarily inoperative, under specific conditions, at the beginning of a flight. This document must be prepared by the operator for their particular aircraft(s) in accordance with a procedure acceptable to the Authority, taking into account the configuration of the aircraft(s) and the applicable operating and maintenance conditions. All items related to the airworthiness of the aircraft and not included in the list are automatically required to be operational. Items of equipment that are not required to be listed are not safety-related, such as galleys and equipment for passenger comfort. Operators must establish an effective procedure for determining whether or not failures that are not listed may affect the airworthiness and/or safety of the operation. The MEL may contain additional guidance material or modified operating and maintenance procedures.

An operator must establish, for each airplane, a Minimum Equipment List (MEL) approved by the Authority. This must be based upon, but be no less restrictive than, the relevant Master Minimum Equipment List (MMEL) (if one exists) accepted by the Authority. An operator must not operate an airplane other than in accordance with the MEL unless permitted by the Authority. Any such permission will in no circumstances permit operation outside the constraints of the MMEL.

Configuration Deviation List (CDL)

The Configuration Deviation List (CDL) allows for continued operations with missing secondary airframe and engine parts. Approval for operating with these parts missing is authorized by an amendment to the Type Certificate (TC), which, as a result, requires an Aircraft Flight Manual (AFM) supplement. Any part not included in the CDL must be considered necessary for flight. Therefore, without a CDL, missing secondary airframe and engine parts would ground the airplane until repair or replacement of the part is accomplished. The aircraft manufacturer develops a proposed CDL for a specific aircraft type. The approval of the CDL is the responsibility of the competent authority of the State of the TC holder.

EASA Part 66: Certifying Staff Requirements

To become certifying staff in a Part 145 organization according to EASA regulations, maintenance personnel must meet basic requirements and understand their limitations regarding their certifying privileges. All this appears in EU1321/2014 Annex 3 Part 66.

Relevant Training and Module Exams

As maintenance personnel in either a Part 147 training school or a recognized training academy, individuals may be required to complete training courses and exams to gain certifying privileges. These courses/exams will define how many years of experience are required later in one’s career to apply for a maintenance license.

Practical Experience Requirements

Experience requirements are broken down into three categories:

  • For subcategories B.1.1, B.1.3, and category B.2:
    • Five years of practical maintenance experience on operating aircraft, if the applicant has no previous relevant technical training; or
    • Three years of practical maintenance experience on operating aircraft and completion of training considered relevant by the competent authority as a skilled worker in a technical trade; or
    • Two years of practical maintenance experience on operating aircraft and completion of a basic training course approved in accordance with Annex IV (Part-147).

License Management

Maintenance workers must keep an up-to-date logbook with all the required information regarding the jobs they have carried out and be able to present such evidence to the authorities. When the required experience is gained, the license will be issued, but without any aircraft type rating unless the type course of the aircraft has been completed and On-the-Job Training (OJT) is presented to the authority that issues the license when Form 19 is submitted.

The authority that issues your license is responsible for modifying it, and your license must be renewed every 5 years to remain valid.

Understanding Certification Limitations

It is especially important to know that once a certifying privilege is granted, individuals must be aware of their scope of certification. Licenses must be reviewed to ensure authorization to certify aircraft by type and category.

EASA Part 66 License Categories

Here are some examples of EASA Part 66 license categories:

  • EASA CAT A: Certified to carry out simple scheduled line replacement unit changes and sign a certificate of release according to their limitations.
  • EASA CAT B1: Certified to carry out scheduled and unscheduled maintenance on most aircraft systems, including some very simple avionic tests.
  • EASA CAT B2: Certified to carry out maintenance of avionic systems within powerplant and mechanical systems, requiring simple steps and minor scheduled maintenance tasks within the limits of their scope.
  • EASA CAT B3: Certified to carry out the same tasks as CAT B1 but for unpressurized piston engine aircraft with a Maximum Take-Off Mass (MTOM) of 2000kg or less.
  • EASA CAT C: Certified to carry out the Certificate of Release to Service (CRS) of an aircraft in its entirety for all base maintenance checks.

International Civil Aviation Organization (ICAO)

The International Civil Aviation Organization (ICAO) is the specialized agency of the United Nations. It was created by the signing of the Convention on International Civil Aviation (also known as the Chicago Convention) in Chicago on December 7, 1944.

ICAO is the permanent body responsible for the administration of the principles set out in the Convention. It has its headquarters in Montreal, Canada, and its European office in Paris.

ICAO consists of 190 signatory states, of which only three are not members.

ICAO’s aims and objectives are to establish the principles and techniques of international air navigation and to promote the planning and development of international air transport.

The ICAO Council has elaborated and adopted 18 technical annexes.

Key ICAO Annexes for Aircraft Maintenance

Most important annexes for aircraft maintenance purposes include:

  • Annex 1: Personnel Licensing
  • Annex 6: Operation of Aircraft
  • Annex 8: Airworthiness of Aircraft
  • Annex 10: Aeronautical Telecommunications

EASA Part 145: Approved Maintenance Organizations

These are the”standar” maintenance organizations. Type Certificate (TC) holders and large aircraft, along with their components, must be maintained in these organizations. They are regulated by Regulation (EU) 1321/2014 and subsequent revisions in Annex II (Part 145). The EASA Part 145 Regulation establishes common technical requirements and administrative procedures for ensuring the continuing airworthiness of aircraft. Part 145 specifies the role of a few key positions in the maintenance organization management hierarchy. The organization must ensure that certifying staff and support staff have an adequate understanding of the relevant aircraft and/or components to be maintained, together with the associated organization procedures.

Key Requirements for Part 145 Organizations

  • The organization must have available and use the necessary equipment, tools, and material to perform the approved scope of work.
  • The organization must hold and use applicable current maintenance data in the performance of maintenance, including modifications and repairs.
  • The organization must record all details of maintenance work carried out.
  • The organization must report to the competent authority, the state of registry, and the organization responsible for the design of the aircraft or component.

Maintenance Organization Exposition (MOE)

Maintenance Organization Exposition (MOE) refers to the documents that contain the material specifying the scope of work deemed to constitute approval and showing how the organization intends to comply with this Annex (Part-145).

The organization must only maintain an aircraft or component for which it is approved when all the necessary facilities, equipment, tooling, material, maintenance data, and certifying staff are available.

Certificate of Release to Service (CRS)

The Certificate of Release to Service (CRS) signifies the transfer of the aircraft from the maintenance organization back to the operators.

EASA Part M: Continuing Airworthiness Management

Part M establishes the requirements to be met by an organization to qualify for the issuance or continuation of an approval for the maintenance of aircraft. These are regulated by Regulation (EU) 1321/2014 and subsequent revisions in Annex I (Part M).

An application for issuance or change of a maintenance organization approval must be made on a form and in a manner established by the competent authority. An organization involved in activities subject to this Subpart must not exercise its activities unless approved by the competent authority. Appendix V to Annex I (Part-M) provides the template certificate for this approval.

Maintenance Organization Manual (MOM)

The maintenance organization must provide a manual containing at least the following information:

  • A statement signed by the accountable manager confirming that the organization will continuously operate in accordance with Annex I (Part-M) and the manual at all times.

To ensure that the approved maintenance organization continues to meet the requirements of this Subpart, it must organize regular organizational reviews.

An approval is issued for an unlimited duration.

Findings Levels

Findings are categorized as:

  • Level 1: A finding that seriously hazards flight safety and lowers the safety standard.
  • Level 2: A finding that could lower the safety standard and possibly hazard flight safety.

Certification Specification (CS-25)

The Certification Specifications (CS-25) are comprehensive documents that define the requirements and capabilities for aircraft in each category. The content of a CS includes:

Content of CS-25

  • Performance
  • Structure
  • Design and Construction
  • Powerplant Installation
  • System and Equipment
  • Manuals and Limitations

Large Airplanes (CS-25)

A Large Aircraft is classified as an airplane with a maximum take-off mass of more than 5,700 kg, or a multi-engined helicopter.

Airplanes powered by turbine engines are subject to CS-25 as their airworthiness code.

Specific operational considerations within CS-25 include:

  • Without contingency thrust, it is not increased following engine failure during take-off, except as specified in sub-paragraph C.

In the absence of an appropriate investigation of operational implications, these requirements do not necessarily cover:

  • Automatic landings with decision heights of less than 200ft.
  • Operations on unprepared runway surfaces.