Lycoming Airworthiness Directives: What Are the Most Common Lycoming ADs?

If you own or fly an aircraft powered by a Lycoming engine, you have almost certainly come across the term airworthiness directive. These are not suggestions or friendly reminders. They are mandatory safety orders issued by the Federal Aviation Administration (FAA), and they carry the full weight of federal law. 

The FAA has issued dozens of Lycoming airworthiness directives over the years, covering everything from valve train wear to connecting rod bushing failures. One of the most widely discussed in recent years is AD 2024-21-02, which targets connecting rod bushings in a broad range of Lycoming engines. Understanding what these directives require — and how to stay current on them — is one of the most important responsibilities you carry as an aircraft owner.

This guide breaks down the most common Lycoming ADs, explains what each one requires, and gives you the practical tools to stay compliant and keep your aircraft flying safely.

Key Takeaways

Lycoming airworthiness directives are mandatory FAA safety orders that require inspections, repairs, or part replacements on affected engine models. The most frequently encountered ones target valve train components, crankshafts, cylinders, oil systems, and connecting rod assemblies. Compliance is not optional — it is a legal requirement, and failure to comply can ground your aircraft and void your insurance. AD 2024-21-02, the most significant recent directive, requires inspection and potential replacement of connecting rod bushings in a wide range of Lycoming engines.

Flying411 is a trusted resource for aircraft owners who want straightforward, expert guidance on engine maintenance, AD compliance, and the real costs of keeping a Lycoming-powered aircraft airworthy. Bookmark it now — you will come back to it.

What Is an Airworthiness Directive (AD)?

An airworthiness directive is an official safety order from the FAA. When the FAA identifies a confirmed safety problem with an aircraft, engine, propeller, or related component, it issues an AD that legally requires specific corrective action. That action might be an inspection, a repair, a part replacement, or a combination of all three.

ADs apply to certificated aircraft and their components. If your engine is listed in an AD, you must comply. The only exception is if the FAA grants an alternative method of compliance, commonly called an AMOC. AMOCs must be applied for and approved — they are not something you can decide on your own.

Good to Know: An AMOC allows an owner or operator to meet an AD's requirements using a different method than what the directive specifies. Your mechanic can help you apply for one through the FAA if a standard compliance method is not feasible.

The Three Types of Airworthiness Directives

Not every AD works the same way. Understanding which type applies to your engine matters, because it directly affects how much time and money compliance will cost over the life of the aircraft.

• One-time ADs — You perform the required action once, document it in the logbook, and the requirement is satisfied. No repeat action needed.
• Recurring ADs — These require inspections or checks at set intervals, such as every 100 hours of operation or at every annual inspection. These add ongoing cost to your maintenance budget.
• Terminating action ADs — Completing a specific repair or replacement permanently resolves the unsafe condition. It requires a larger upfront investment but eliminates future repeat compliance steps.

Why It Matters: Recurring ADs are often the ones that surprise new aircraft owners. If you buy a used aircraft, make sure you know which recurring ADs apply — and how frequently they come due — before you finalize the purchase.

The Legal Foundation of ADs

Congress grants the FAA the authority to issue and enforce airworthiness directives as part of its mission to promote safe flight in civil aviation. The FAA publishes ADs in the Federal Register, which gives them the force of law under Title 14 of the Code of Federal Regulations. Ignoring an AD is not just a maintenance oversight — it is a violation of federal regulation.

For Lycoming engine owners, this means that staying on top of ADs is not optional. It is part of operating legally and responsibly. Some directives are straightforward and low-cost. Others, like those involving connecting rod bushing inspections or crankshaft replacements, require careful coordination with a qualified mechanic and can involve meaningful expense.

Heads Up: Ignoring an AD does not just risk safety — it can void your aviation insurance and expose you to FAA civil penalties. An aircraft with an open or overdue AD is considered legally unairworthy.

Why the FAA Issues ADs for Lycoming Engines

ADs are issued because real safety issues were identified. They are not issued lightly. When the FAA publishes a directive targeting a specific Lycoming engine component, it is typically because there were documented cases of failures in service — sometimes serious ones.

A recent example is AD 2024-21-02, issued in late 2024 after multiple reports of connecting rod failures causing engine shutdowns in flight. The directive was prompted by findings of degraded connecting rod bushing material in certain Lycoming engine models. It was published in the Federal Register on October 31, 2024, and coordinated closely with Lycoming Mandatory Service Bulletin MSB 630A. If you want to understand what a proper engine inspection looks like leading up to an event like this, the guide on Lycoming borescope inspection covers the full process in detail.

How Lycoming ADs Affect Engine Owners

Owning a Lycoming-powered aircraft means keeping close track of every AD that applies to your specific engine model and serial number. The impact goes well beyond safety — ADs affect your budget, your maintenance calendar, and even your aircraft's resale value.

Compliance Is Mandatory — No Exceptions

This point cannot be overstated. If an AD applies to your engine and you have not complied, your aircraft is considered legally unairworthy. You cannot fly it. The FAA sets compliance deadlines — sometimes measured in flight hours, sometimes by calendar date. Missing those deadlines has real consequences.

Some owners assume that if the engine seems to be running fine, compliance can wait. That is not how ADs work. The directive exists precisely because there may be no visible symptoms before a failure occurs. The compliance window is not a suggestion — it is a legal boundary.

Pro Tip: Keep a dedicated AD compliance log separate from your regular maintenance entries. Organizing ADs by type — one-time, recurring, or terminating — makes it much easier to track what is coming due and when.

How ADs Affect Your Maintenance Budget

ADs add real cost to aircraft ownership. Recurring ADs in particular require ongoing attention and labor. Here is a general breakdown of what compliance typically involves:

• Labor costs — A certified mechanic must perform and sign off on all required work
• Parts costs — Some ADs require replacement of specific components using FAA-approved parts
• Downtime — Your aircraft may need to be grounded while the work is completed
• Documentation — Every AD compliance action must be properly logged with the mechanic's certificate number and signature

For a deeper look at what Lycoming maintenance can cost over time, the guide on the Lycoming 50-hour inspection is a helpful reference for understanding routine maintenance intervals and what shops typically check.

Keep in Mind: Some ADs require parts from a specific approved source. Using non-approved parts — even if they appear identical — does not satisfy the AD and can create legal and insurance complications.

ADs and Aircraft Resale Value

If you ever plan to sell your aircraft, AD compliance history matters enormously. Buyers and their mechanics will review logbooks carefully during any pre-purchase inspection. Missing or poorly documented AD compliance is a serious red flag that can reduce your aircraft's value or derail the sale entirely.

A clean, well-documented compliance history tells buyers the aircraft was properly maintained. It builds confidence and supports a stronger asking price. Treat AD documentation as an investment in the aircraft's long-term value — not just a regulatory chore.

The Most Common Lycoming Airworthiness Directives

Lycoming has one of the longest histories in general aviation piston engines, and with that history comes a substantial catalog of ADs issued over the decades. Some target a narrow range of serial numbers. Others apply broadly across many model families. Here is a breakdown of the most significant and frequently referenced directives.

AD 80-04-03: Valve Train Inspection

This is one of the most well-known and long-standing Lycoming ADs. AD 80-04-03 addresses wear and damage in the valve train — specifically the rocker arms, push rods, and related components. It has been on the radar of mechanics and owners for decades, which means most engines in active service have established compliance histories. That said, it still must be tracked and verified during pre-purchase inspections and annual reviews.

If you want to understand the physical condition of these components during an inspection, the Lycoming camshaft inspection guide covers related valve train inspection procedures in useful detail.

Fun Fact: AD 80-04-03 has been in effect for so long that many mechanics have memorized its requirements. However, "everyone knows it" does not mean it is always documented correctly — always verify the logbook entry.

Crankshaft-Related ADs

Several ADs over the years have targeted Lycoming crankshafts, one of the most structurally critical components in any reciprocating engine. Crankshaft issues can lead to catastrophic engine failure if not identified and addressed early. When the FAA identifies a pattern of crankshaft-related incidents across a population of Lycoming engines, an AD is typically issued to require proactive inspections before additional failures occur.

Common crankshaft AD requirements include:

• Ultrasonic or magnetic particle inspection of the crankshaft
• Replacement of crankshafts that show evidence of cracking or wear
• Compliance tied to total engine time or triggered at overhaul

Crankshaft failures are relatively rare but carry severe consequences when they do occur. These ADs exist because the FAA wants to catch early-stage degradation before it reaches the point of failure.

Why It Matters: Crankshaft ADs are often triggered at overhaul, which makes them easy to overlook on low-time engines. If your engine is approaching its time between overhaul (TBO), confirming crankshaft AD compliance should be on your checklist.

Cylinder and Piston ADs

Cylinder and piston issues have generated a meaningful number of ADs for Lycoming engines over the years. These directives typically focus on cracks, manufacturing defects, or wear patterns that could cause power loss or internal engine damage. Borescope inspection of cylinder walls is a standard compliance method for many of these ADs.

Common requirements include:

• Borescope inspection of cylinder walls for cracks or scoring
• Inspection of piston pins and rings for wear or deformation
• Replacement of affected cylinders or pistons before return to service

Many ADs in this category target specific production runs or time-in-service ranges. For more context on what cylinder inspectors are watching for, the Lycoming cylinder corrosion guide walks through the key signs of developing problems.

Quick Tip: Cylinder condition is one of the best indicators of overall engine health. A scheduled borescope inspection — even outside of AD requirements — can give you early warning of developing problems before they become compliance issues.

Oil System and Accessory ADs

Oil system ADs are among the more frequently encountered directives for Lycoming owners. These address issues with oil pumps, oil screens, oil filter adapters, and related accessories. Many align naturally with routine oil change intervals, which makes them relatively straightforward to fold into regular maintenance.

Inspecting the engine oil filter at each oil change is a simple but high-value habit. Metal particles in the filter can be early indicators of internal engine problems — including bearing wear or early-stage connecting rod assembly issues. Detecting these particles early can help you address a developing problem before it escalates into an AD-level failure.

Keep in Mind: Documenting every oil system AD compliance action is just as important as doing the work. An undocumented inspection provides no legal protection and no paper trail for future buyers.

AD 2024-21-02: Connecting Rod Bushing AD

This is the most significant and widely discussed Lycoming directive in recent years. AD 2024-21-02 was issued by the FAA after multiple documented reports of connecting rod failures that led to uncontained engine failures — one of the most dangerous events in aviation. The directive was published in the Federal Register on October 31, 2024, and developed in coordination with Lycoming Mandatory Service Bulletin MSB 630A.

Heads Up: Uncontained engine failure — where engine parts break through the cowling — is among the most serious failure modes in piston aviation. AD 2024-21-02 was issued specifically because this type of failure was documented in the field.

The FAA determined that connecting rod bushing material in certain Lycoming engines degrades over time, particularly in engines with high operating cycles. This degradation weakens the connecting rod assembly and can eventually lead to rod failure.

What the AD requires in practice:

• Inspection of connecting rod bushings for wear, degradation, or damage
• Recurring inspection at specified intervals if bushings are not immediately replaced
• Replacement of connecting rod bushings if they fail inspection criteria
• In some cases, replacement of the connecting rod assembly itself
• Engine oil filter inspection as a supporting step to detect early signs of internal wear

Affected connecting rod assemblies are identified by specific part number ranges. Owners should check the FAA AD docket for their specific engine model and serial number to confirm applicability. Terminating action — the step that ends the recurring inspection requirement — is achieved through full replacement with approved parts listed in Table 3 of Lycoming MSB 480F and MSB 630A.

ℹ️ Good to Know: Rod bushings eligible for terminating action are specifically listed in the service bulletin tables. Not all replacement parts qualify — confirm part numbers with your mechanic before ordering.

For owners who are facing a significant parts replacement and want to understand the broader cost picture, the guide on breaking in a new Lycoming engine provides helpful context on what comes next after major engine work.

Lycoming ADs at a Glance: Quick Comparison

How to Check AD Compliance on a Lycoming Engine

Confirming which ADs apply to your engine — and that they have been properly addressed — is a fundamental responsibility of aircraft ownership. Here is how to do it systematically.

Using the FAA AD Database

The FAA maintains a free, searchable online database of all active airworthiness directives at rgl.faa.gov. You can search by manufacturer, engine model, and serial number. This is the most reliable way to get a current and complete list of ADs that apply to your specific Lycoming engine.

1. Go to rgl.faa.gov and select Engines as the product type
2. Enter Lycoming as the manufacturer
3. Filter by your specific engine model
4. Review each active AD for its effective date, compliance methods, and any approved AMOCs

Pro Tip: The FAA also offers free email notifications that alert you when new ADs are issued for your engine model. Sign up through the FAA website and you will never miss a new directive.

Reading Engine Logbooks for AD Compliance

Every AD compliance action must be entered in the engine logbook. When reviewing a logbook — whether your own or a prospective purchase — look for the following in each entry:

• The AD number (for example, AD 2024-21-02)
• The date on which compliance was completed
• The method used — inspection, replacement, or other approved action
• The mechanic's signature and FAA certificate number

If a logbook entry is missing or incomplete, that is a problem. It may mean the work was not done, or it was not documented correctly. Either way, it must be resolved before the next flight.

What to Look for During a Pre-Purchase Inspection

A pre-purchase inspection is your best opportunity to catch AD compliance gaps before they become your financial and legal responsibility. Ask the seller for complete logbooks going back as far as available. Have a qualified mechanic — ideally one with specific experience on Lycoming engines — review the records against the current FAA AD database. The Lycoming borescope inspection guide gives useful context on what a thorough inspection of engine internals involves.

Key things to check:

• Is every AD in the FAA database accounted for in the logbook?
• Are recurring ADs current based on the engine's current hours?
• Are there any open or overdue ADs that require immediate action?
• Is there documentation for the most recent compliance with AD 2024-21-02 if the engine model is affected?

Keep in Mind: Missing logbook entries are not always dishonest — sometimes records are simply lost. But unverifiable AD compliance is a legitimate concern that can affect the aircraft's value and insurability. Always verify before you buy.

Working With Your Mechanic on AD Compliance

A knowledgeable A&P mechanic — especially one holding an Inspection Authorization (IA) — is your best partner in AD compliance. They should be familiar with the FAA's airworthiness products database and know how to access current information. Ask your mechanic to perform a full AD compliance review as part of every annual inspection. This gives you an updated snapshot of where things stand and flags anything new or coming due.

Staying Current: How New ADs Are Issued

The FAA's AD Rulemaking Process

New ADs begin with a confirmed safety concern — typically sourced from accident reports, service difficulty reports filed by operators, or data submitted by the manufacturer. In the case of AD 2024-21-02, the FAA reviewed Lycoming data on connecting rod bushing degradation before issuing the directive. The process typically works like this:

1. A safety issue is identified and documented
2. The FAA publishes a Notice of Proposed Rulemaking (NPRM) for public comment
3. Industry feedback is reviewed and evaluated
4. The final AD is published in the Federal Register and becomes enforceable

This process gives manufacturers, mechanics, and owners an opportunity to provide input before a directive becomes final.

Fun Fact: The NPRM process means that major ADs are rarely a complete surprise to the aviation maintenance community. When the proposed rule for AD 2024-21-02 was published, many mechanics were already preparing before the final rule went into effect.

Lycoming Service Bulletins vs. Airworthiness Directives

Not every safety notice from Lycoming is an AD. Lycoming regularly publishes service bulletins (SBs), mandatory service bulletins (MSBs), and service instructions that recommend maintenance actions. Service bulletins are not legally required unless the FAA formally incorporates them into an AD.

That said, the line between a recommendation and a legal requirement can blur. Lycoming MSB 630A, for example, provided the technical foundation for AD 2024-21-02. When the FAA adopted its requirements into a formal AD, compliance became mandatory. This is a common pattern — a service bulletin that addresses a serious enough safety risk often becomes the basis for a formal directive.

Paying attention to MSBs — even before they become ADs — is good practice. It can give you lead time to plan for compliance, source parts, and schedule your aircraft's downtime before a hard deadline is imposed.

Quick Tip: Subscribe to Lycoming's service document notifications in addition to FAA AD alerts. An MSB published today could become a legally required AD within months.

Conclusion

Lycoming airworthiness directives are not optional, not negotiable, and not something to push to the back of your maintenance calendar. They exist because real safety problems were identified in the field — and complying with them is what keeps you, your passengers, and others around you safe. From the long-standing valve train inspections of AD 80-04-03 to the urgency of the 2024 connecting rod bushing directive, each AD has a clear purpose and a legal deadline.

Staying current on your ADs does not have to feel overwhelming. With the right systems in place — a dedicated compliance log, regular AD database checks, FAA email alerts, and a knowledgeable mechanic — you can manage this responsibility as a routine part of aircraft ownership rather than a crisis waiting to happen.

If you want to keep learning and stay sharp on engine maintenance, airworthiness compliance, and the real costs of keeping a Lycoming-powered aircraft in the air, Flying411 is a great place to dig deeper. 

Frequently Asked Questions

What happens if I don't comply with a Lycoming AD?

Flying an aircraft with an overdue or incomplete AD makes it legally unairworthy under FAA regulations. You could face civil penalties, and your aviation insurance may be voided in the event of an incident or claim. The aircraft must remain grounded until compliance is completed and properly documented by a certified mechanic. There are no grace periods once a compliance deadline has passed.

Can I perform AD compliance work myself on my Lycoming engine?

Most AD compliance work must be performed and signed off by an FAA-certified mechanic holding an Airframe and Powerplant (A&P) certificate, and many items also require an Inspection Authorization (IA). While FAR Part 43 does allow certain owner-performed maintenance tasks, anything involving engine internals almost always requires a licensed professional. Always confirm the specific requirements with your mechanic before attempting any work on your own.

How do I know if a specific AD applies to my Lycoming engine's serial number?

Each AD lists the specific engine models, series, and serial number ranges it covers. You can look this up using the FAA's online AD search tool at rgl.faa.gov by entering your engine manufacturer and model. Your mechanic can also cross-reference the engine's data plate information against the AD directly to confirm whether your specific unit is affected.

Are Lycoming service bulletins the same as airworthiness directives?

No, they are different. Service bulletins are issued by Lycoming and are typically recommendations, not legal requirements — unless the FAA formally incorporates them into an AD. Once the FAA adopts a service bulletin's requirements into an official directive, compliance becomes mandatory for all affected aircraft owners under federal regulations. Lycoming MSB 630A, for example, became the technical backbone of the mandatory AD 2024-21-02.

How often should I check for new ADs affecting my Lycoming engine?

It is a good habit to check for new ADs at least quarterly, and always before purchasing a used aircraft with a Lycoming engine. Signing up for FAA email notifications for your engine model is the easiest way to stay current automatically. Your mechanic should also perform a full AD compliance review during every annual inspection to catch anything new or coming due.

What is the compliance timeline for AD 2024-21-02?

The specific compliance windows depend on your engine model, part numbers, and current hours. The AD specifies different timelines for initial inspection versus ongoing recurring inspections. Terminating action — replacing the affected bushings with approved parts — ends the recurring requirement. Check the AD docket and Lycoming MSB 630A for the exact timelines that apply to your engine configuration, and work with your mechanic to schedule accordingly.

Does AD compliance affect my aircraft's insurability?

Yes, it can. Most aviation insurance policies require that the aircraft be maintained in an airworthy condition, which legally includes full AD compliance. If an incident or accident occurs while an AD is open or overdue, the insurer may have grounds to deny the claim. This is a significant financial risk on top of the safety and regulatory concerns. Staying current on ADs protects both your safety and your coverage.

Where can I find the parts eligible for terminating action under AD 2024-21-02?

The parts eligible for terminating action are listed in Table 3 of Lycoming Mandatory Service Bulletins MSB 480F and MSB 630A. Your mechanic or engine shop should have access to these documents. You can also find them through Lycoming's official service document portal or the FAA AD docket.