The Crucial Role of Safety Directives on Aircraft.

How do aircraft operators know an unforeseen circumstance will jeopardize the safety of the aircraft and its passengers? The Service Bulletin and Airworthiness Directives might provide the answer.

Nazmi Izwan
7 min readNov 14, 2020


Malaysia Airlines’ fleet in Kuala Lumpur International Airport at sunset. Image by Author

The aviation industry is surrounded by strict and non-compromising rules that have been set internationally. No other operators, manufacturers, or persons that freely escape this modulated and controlled system. The international regulatory body and the local aviation authority, together with the manufacturers, airlines, operators, and MROs always in contact with one-way and two-way communications for safety purposes.

Every nook and cranny of matters that arise require the need for documentation, recording it, and solving it to help reduce potential risks any further. All situation arises need to be reported for the local and international authorities to be aware of from the smallest circumstances of a missing tool to major incidents and accidents.

In this safety series, we will look into how and what triggers the regulatory in issuing a safety directive about an impending safety risk on an aircraft hence the reason why you probably shouldn’t feel fear when boarding one.


Before we begin, we should know who and what the related agencies are for in implementing the rules and regulations for safety in the aviation industry. The Federal Aviation Administration (FAA) of the United States and the European Union Aviation Safety Agency (EASA) are the prime regulatory bodies to monitor all the industry’s activities alongside the IATA and ICAO.

They will actively keep track of major and even minor incidents and safety-related occurrences that arise from around the world. They are like the parent that look after a newborn and always keep an eye on the baby. The two bodies are working together regularly for ;

  • the process of certifying aircraft,
  • monitoring the operators to comply with the strict regulations,
  • set the rules and guidelines for the approved maintenance organization in conducting repairs and overhaul for the aircraft and its components,
  • providing and approving the license for both the pilots and engineers,
  • auditing all the operators and the manufacturers,
  • producing a certificate for new or repaired/overhauled components that conformed the items were in good condition and tested/inspected as per the approved manual.

These are what the authorities execute but are not limited to these only. There are many more comprehensive scopes of work done by them. Nevertheless, these are good to know without absorbing too much information.


One of the reasons aviation is the safest mode of transportation is the strict laws enforced on it. These include the Service Bulletin and Airworthiness Directive. What are those? What is common between these two and what do they tell us? What is the significance of having these two? And what are the differences? These two unquestionably play significant parts in managing the safety of an airplane.

For the record, the authority and the manufacturer should be made aware of bits and pieces of events that threaten the safety of the aircraft and its surrounding. These include any major or minor incident that happened. From there, the related body will investigate to identify the root cause of the problem.

The FAA and EASA have the power to make the ADs / SBs as a short-term solution to rectify the obstacle while cracking the code of the event that could take a long time. Those ADs / SBs could also potentially make the current procedures or maintenance program obsolete as it is replaced by the improved one to tailor the need for a long-term solution. Does that mean the aircraft certification process was improperly done? Or it is overlooked by the authority? Or a badly designed configuration could lead to unsafe conditions over time?

With that being said, these ADs and SBs provide vital insight and a deep understanding of aircraft behavior over time. It is wrong to assume that safety research and analytic data were taken for granted during the designing and certifying phased. I’m not saying that the test data were not comprehensive enough or lacked thereof. Yes, it takes engineers thousand of hours and data to replicate the worst-case scenario that could happen during the entire life of the aircraft and its components.

But, some technical difficulties happened when a combination of unique circumstances occur while aircraft are flown in real-world conditions.

So, what is SB, and what is AD?

SB or Service Bulletin is the way the manufacturer, in this case, are Boeing; Airbus; Bombardier; or Embraer inform the operator of the said aircraft about a recent discovery of occasions where it affects the operation or the performance but, within the safety margin of the aircraft’s design nevertheless.

One of the Service Bulletins for a Boeing 737. Image by Author.

The operator should take a precautionary step or steps according to that particular SB to solve it. If not, it may say, for example, affect the fuel consumption or increase the workload of the crew or anything else that consider minor. This SB, if found concerning enough by the authority, could be amended and changed to AD or Airworthiness Directive.

ADs are implemented by the authority for alerting all the affected aircraft operators around the globe of an issue or issues that can jeopardize the safety of the aircraft and its passenger. The operator must comply with all the steps or rules within the AD. If not, the jet is in an unairworthy condition to fly. It is not a choice given to the operator but a mandatory one.

Let me give you an example for better clarity. Recently, the FAA has made aware of one or two cases in which several aircraft have issues on one of its components that prompt the engine to shut down mid-flight. After a thorough investigation, a corroded valve in the engine was the culprit. It corroded due to long-term parking.

Because of this pandemic, flying is not a choice thus aircraft remain on the ground for long-term parking, which in some parts of the world, high humidity and higher salt concentration in the air worsening the condition.

The location of the said valve in the CFM 56 high bypass engine with its cowling opened. Image by Author.

So, the authority released an AD to check and inspect the related component plus replace it if it’s deemed necessary so by the instructions in the AD itself or the manual before the aircraft could fly.

The task must be signed off by the engineer to verify that it has been completed and tested accordingly. It is needed to fulfill all the procedures in the AD before it is permitted to fly. Bear in mind that it is affecting ALL versions of the specific aircraft.

Emergency Airworthiness Directive for the inspection of a bleed air valve. Image by Author.

Importance of Airworthiness Directive

An aircraft cannot fly if it doesn’t have the required certificates to allow it to do so. One of them is the annually-renewed Certificate of Airworthiness. It is a statement that the said aircraft conform to the original specification, which means that scheduled and ad hoc maintenances have been completed, plus all specifications and performances behave like how it is certified. These include the ADs requirement.

Without fulfilling the mandatory requirement, the authority will not be issuing the certificate, so the aircraft is prohibited from flying. The regulator can even revoke the certificate effective immediately if it found any unsatisfactory issues.

From another point of view, a lessee, which is usually the operator will consider leasing an aircraft that has implemented all the ADs to date as their requirement. The operator will then thoroughly reviewed the maintenance history before negotiating the price with the lessor. If the previous operator properly maintained the aircraft and documented it well, it might help in selling it like hotcakes.

The airplane that you flew or will fly with is safe and adhere to the ADs and SBs that imply for that particular aircraft type. Whether you are flying with a brand new aircraft or 20+ years old one, rest assured that the safety of the older aircraft has never been compromised, even on par with the brand new one. If the jet is reaching its 15 or older years mark, it also means that it has complied with numerous ADs along its lifetime.

Also important to note, a brand new aircraft exiting the production line will be equipped and updated with the AD’s compliance before being delivered to the customer. The manufacturer, the authority, and even universities and other related bodies ( eg; a metallurgist, or Naval Air Warfare Center for analyzing multiple uncontained engine failures) will study all the gathered data from the directives themselves.

If found any breakthrough from the research, they will evaluate the effectiveness and consequences before implying those corrective measurements into the next brand new aircraft projects. All of these are to ensure that the commercial aircraft are constantly up-to-date with all the relevant safety nets and not a single of them missed the train.

All in all, the aviation industry is continuously evolving. If there is something that come up that has to be improved and updated, none of the aircraft or operators are left behind. Numerous minor and major incident reports around the globe plus well-reviewed analytic data and researches make up all the information needed for the authority and concerned parties to help improve the safety risk imposed on millions of passengers as well as the ‘health’ of million dollars aircraft.



Nazmi Izwan
Writer for

Aviation made simple and understandable for general flying public.