The aviation industry is one of the most highly regulated sectors in the world, and rightly so — human lives depend on the airworthiness of aircraft being maintained to the highest possible standard.
In the lifecycle of an aircraft, the role of ongoing inspections, modifications, and technical compliance measures is crucial. Two of the most important tools that drive such measures are Service Bulletins (SBs) and Airworthiness Directives (ADs).
These documents serve as official mechanisms for maintaining, restoring, or improving the safety, reliability, and compliance of aircraft and their components. In this article, we’ll explore what SBs and ADs are, how they’re created, how they differ, and how they are managed and implemented within an aircraft operator’s maintenance system.
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What are service bulletins (SBs)?
A Service Bulletin (SB) is a technical document issued by an aircraft, engine, or component manufacturer. Its primary purpose is to notify aircraft operators and maintenance organisations of recommended actions that should be taken to address a particular issue, improvement opportunity, or regulatory request. These actions might include an inspection, a part replacement, a system modification, or even just procedural updates.
Crucially, SBs can be adopted voluntarily by the aircraft operator unless they are referenced by a mandatory regulatory document such as an Airworthiness Directive.
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Are Service Bulletins (SBs) mandatory?
Great question — and one that causes a lot of confusion, even among people in aviation!
No, service bulletins (SBs) are not mandatory by default.
They are recommendations issued by manufacturers — such as aircraft OEMs (like Airbus or Boeing), engine makers (e.g., Rolls-Royce, GE, Honeywell), or component suppliers — to advise operators on inspections, modifications, or updates that may improve safety, performance, or reliability.
However...
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⚠️ When do service bulletins become mandatory?
An SB can become mandatory if it is:
- Referenced in an Airworthiness Directive (AD) (More on these later in the article)
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- If EASA, the FAA, CAA or another national aviation authority determines that an unsafe condition exists, they may issue an AD Â
- Often, this AD will require compliance using the method described in the manufacturer’s SB Â
- In this case, the SB becomes mandatory because it’s now legally enforceable via the AD
 - Required by a customer contract or lease agreement
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- Some aircraft leasing companies or airline internal policies may require certain SBs to be performed to maintain asset value or fleet standardisation
 - Incorporated into the Approved Maintenance Programme (AMP)
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- If an operator voluntarily adds an SB into its AMP, it effectively becomes mandatory for that operator, and must be carried out as scheduled
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Why are service bulletins issued?
Manufacturers monitor the performance and safety of their products long after they’ve left the factory. Using in-service data, reports from airlines, feedback from maintenance crews, and regulatory input, they detect patterns or weaknesses that may not have been obvious during design or initial certification. When an issue is identified that warrants technical intervention, the manufacturer will often address it through a Service Bulletin.
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Understanding the reasons to issue an SB
These bulletins are issued for several reasons, all aimed at maintaining and improving safety, performance, and compliance. Often, an SB is triggered by the discovery of a potential safety risk or a trend indicating premature failure in a component. Field reports from operators might highlight unexpected wear, unusual performance, or outright malfunctions, prompting further investigation.
Sometimes, the impetus comes from within the manufacturer’s own design teams, who may identify opportunities for upgrades or implement improvements as new technologies become available. Regulatory changes—such as those affecting noise emissions or environmental standards—can also necessitate updates via SBs. Additionally, feedback from airline customers, or lessons learned from incident and accident investigations, often shapes the content of a new bulletin. By issuing SBs, manufacturers help ensure that vital safety information is disseminated throughout the global operator community, allowing for proactive risk management.
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How Are Service Bulletins Produced?
Creating a Service Bulletin is not a casual task—it is a detailed engineering and documentation process built on rigorous standards of accuracy, clarity, and traceability. The process begins with the identification of an issue. This could emerge from safety reporting systems, maintenance data analysis, performance monitoring across the fleet, or findings from internal inspections and audits.
Once an issue is flagged, it undergoes a formal engineering investigation. Experts work to assess the severity of the risk, identify root causes, and evaluate the potential impact on aircraft safety or performance. Based on these findings, a solution is developed. This might take the form of a component replacement, an updated inspection procedure, structural reinforcement, a software patch, or any number of corrective actions tailored to the specific problem.
The technical fix is then formalised into a Service Bulletin. A typical SB includes several key elements: background and scope, applicability by aircraft or component type, detailed instructions for carrying out the task, required parts and tools, estimated labour time, and supporting diagrams or drawings.
Before the bulletin is published, it must pass through an internal review process involving engineering, quality assurance, and legal teams. These reviews ensure that safety implications are thoroughly considered and that the information is legally sound. Once approved, the SB is distributed to operators via OEM technical portals, direct emails, or integration into maintenance tracking platforms such as AMOS or CAMP.
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Incorporating SBs Into Aircraft Maintenance
Once an operator receives an SB, there are generally two paths to consider: voluntary or mandatory incorporation.
In the case of voluntary adoption, operators review the recommendations and decide, based on factors such as safety enhancement, cost efficiency, or fleet standardisation, whether to implement the changes. Even in the absence of a regulatory requirement, many airlines choose to comply with SBs that promise longer-term savings, better reliability, or reduced risk of future mandatory directives. If they choose to proceed, the SB is integrated into the Approved Maintenance Programme (AMP) and scheduled accordingly.
However, not all SBs remain voluntary. In cases where a significant safety issue is identified, regulatory bodies such as EASA, the FAA, or the UK CAA may issue an Airworthiness Directive (AD) that mandates compliance with all or part of a particular SB.
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What is an Airworthiness Directive (AD)?
An Airworthiness Directive is a legally binding instruction issued by a civil aviation authority that requires specific corrective actions to be taken on an aircraft, engine, or component to address an unsafe condition. According to EASA Regulation (EU) No. 748/2012, Annex I (Part 21), an AD is defined as a directive issued to restore an acceptable level of safety when a specific risk has been identified.
Under section 21.A.3B(b), an AD must be issued when an unsafe condition exists in an aircraft or component, and there is a likelihood that the same issue could develop in other aircraft of the same type. The manufacturer, acting as the Type Certificate Holder or design authority, plays a central role in this process. They are responsible for proposing corrective actions—often through the issuance of an SB—and submitting these to the relevant authority for approval. Once approved, the AD becomes a formal, mandatory requirement.
An AD typically includes a description of the unsafe condition, a list of affected aircraft or serial numbers, required corrective actions, compliance deadlines, and the date it comes into effect. Operators are legally obligated to follow the directive; failure to do so can result in penalties, regulatory findings, or even the grounding of aircraft.
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Implementation at the Operator Level
When an SB or AD arrives, operators follow a structured, methodical process to evaluate and implement the required actions. The first step is to determine whether the bulletin applies to specific aircraft or components in their fleet. This is followed by an assessment of how the required work will impact operations in terms of cost, downtime, manpower, and overall feasibility.
For voluntary SBs, the operator must make a strategic decision on whether to proceed. In the case of ADs, the decision is already made: compliance is mandatory. Once the decision is made, the work is scheduled and executed in accordance with the instructions provided. Upon completion, all actions are recorded and certified in the aircraft’s technical records. If the action has long-term implications—such as recurring inspections or maintenance intervals—the AMP is updated accordingly.
This comprehensive approach ensures that aircraft remain airworthy, safe, and compliant with both manufacturer guidance and regulatory requirements. It also guarantees traceability and audit readiness—critical components of any operator's safety and quality assurance framework.
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Tracking and auditing
In large fleets, managing hundreds of SBs and ADs across various aircraft types can be a massive task. That's why operators rely on systems and processes to track their compliance status.
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Key stakeholders:
CAMOs (Continuing Airworthiness Management Organisations): Responsible for ensuring continuous compliance with ADs and maintenance programmes.
Maintenance Control Centres: Monitor upcoming SBs/ADs and plan work accordingly.
Quality departments: Conduct internal audits to ensure compliance.
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Audits:
Regulatory authorities such as EASA, the UK CAA, or the FAA frequently audit operators. Non-compliance with ADs or poor SB management can result in serious findings, fines, or even grounding of aircraft.
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How SBs and ADs differ
While they can seem similar, SBs and ADs serve different roles:
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Final thoughts
Aircraft maintenance is more than just fixing things when they break. It's a structured, proactive system built on data, engineering, and regulation. Service Bulletins are a key part of this system — they represent the manufacturer's ongoing commitment to the safety and evolution of their product. Meanwhile, Airworthiness Directives provide the regulatory teeth to enforce action when safety is at risk.
For operators, understanding and managing both is not just about compliance — it’s about preserving the integrity of the aircraft, protecting passengers, and maintaining the trust that the aviation industry depends on.
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