Over the course of a year, regulators, such as the Federal Aviation Administration (FAA) or European Union Aviation Safety Agency (EASA), publish hundreds of airworthiness directives (AD) to address a variety of safety conditions in commercial, general aviation, and military aircraft. The directives also affect helicopters and aircraft engines, all with one goal in mind: to ensure the flying public’s safety.
These directives tackle issues small and large, such as the most recent Emergency AD (EAD) published by the FAA to address the Boeing 737 MAX 9 door plug incident. In the EAD, the United States (US)-based regulator said that to prevent potential injury to the passengers and crew onboard the aircraft type, it is grounding 737 MAX 9s “until the airplane is inspected and all applicable corrective actions have been performed using a method approved” by an FAA manager.
1Stakeholders are invited to comment on the directive
In the US, there are 60 days to comment on the directive
Typical AD process:
- A proposed rulemaking
- Stakeholders comment on it, expressing concerns or asking for clarification
- Regulator publishes a final rule AD
However, not all ADs follow the same procedure. For example, the typical process for a directive in the United States is that first, the regulator publishes a Notice of Proposed Rulemaking (NPRM). Then, relevant parties, such as operators, manufacturers, or maintenance organizations, have 60 days to provide their comments about the subject, including requests for clarification or disagreements about the methods of compliance.
Subsequently, the FAA publishes a final rule AD, which also addresses the comments or concerns of relevant stakeholders. A similar process occurs in Europe, where EASA initially issues a Proposed AD (PAD). However, the FAA has a process, such as publishing a final rule directive with a request for comments or an EAD.
Alaska Airlines and United Airlines are the largest operators of the -9 variant.
2FAA provides cost estimates
FAA’s estimates are only for US-based operators
FAA’s cost estimates are split into:
- Labor
- Parts
Every FAA directive comes with an estimate on how many aircraft or engines in the US are going to be affected by the AD. For example, when the regulator said that operators would have to inspect the CFM International CFM LEAP-1A engine powering the A320neo aircraft family, it estimated that only one engine in the country would be affected by the directive.
However, it still provided a cost estimate for operators. The directive, which required airlines to replace an interstage seal on the engine’s high-pressure turbine (HPT), would require airlines to spend $187,125 per engine. The cost is split between parts ($168,000) and labor ($85 per hour multiplied by 225 work hours, $19,125).
The FAA’s proposed directive follows EASA’s proposed directive for the same issue.
3Published for aircraft and engines separately
Aircraft and aircraft engines have separate directives
Examples include:
- FAA directive for an Airbus A380 engine
- EASA and FAA directive for the CFM LEAP-1A engine
Since aviation is a global industry, there are times when aircraft that are manufactured and assembled in Europe could be impacted by an AD, which was published for an engine that is built in the US. For example, the Airbus A380 has two engine options: the Rolls-Royce Trent 900 or the Engine Alliance GP7000.
While Rolls-Royce’s Germany-based subsidiary has the type certificate (TC) of the Trent 900, meaning it falls under EASA’s jurisdiction, like the aircraft, Engine Alliance is based in the US. The General Electric (GE) and Pratt & Whitney joint venture has had 11 final rule ADs published by the FAA, with the most recent being in September 2023.
Engine alliances have delivered some of the best products in the market.
4Led by the state of design’s authority
FAA is responsible for Boeing directives, while EASA is for Airbus’ ADs
Responsible regulators:
- FAA for Boeing
- EASA for Airbus
- National Civil Aviation Agency (Agência Nacional de Aviação Civil, ANAC) for Embraer
- Transport Canada (TC) for Bombardier/Airbus A220
Similar rules apply to aircraft manufacturers as well. EASA is responsible for issuing directives for Airbus, the FAA publishes them for Boeing aircraft, and Brazil’s National Civil Aviation Agency (Agência Nacional de Aviação Civil, ANAC) is responsible for the safety of Embraer products. Interestingly, Transport Canada (TC), in whose jurisdiction are Bombardier and De Havilland Canada products, is also responsible for the Airbus A220 family, since Bombardier obtained the initial certificate and later sold it to Airbus Canada, the European manufacturer’s Canadian subsidiary, which produces the A220 to this day.
According to EASA, some TCs have been known to move between jurisdictions, such as the certificates of the Bell 206 and 222 helicopters moving from the US to Canada. The European regulator noted that a directive is “State of Design AD when the authority that issues the AD is, on the date of issuance of that AD, the State of Design authority for the products, parts or appliances (or STC modification) to which the AD applies.”
The FAA has issued an Emergency Airworthiness Directive for the Airbus A220 to make pilots aware of the dangers.
5Based on the manufacturer’s instructions
All directives are based on Service Bulletins (SB) or other information
Possible instructions:
- Service Bulletins (SB)
- Service Letter (SL)
- Multi-operator Message (MOM)
Each directive is typically based on some sort of compliance instructions from the Original Equipment Manufacturers (OEM), which can come in the form of a Service Bulletin (SB) or a Multi-operator Message (MOM). On January 3, 2024, the FAA published a final rule AD for the Boeing 787 family, addressing under-torqued nuts for flight attendants’ seats.
The regulator said that it reviewed Boeing’s SL 787–SL–25–025, dated September 6, 2022, which specifies procedures to re-torque each free-standing flight attendant seat track fitting nut. The FAA identified it as being related to the directive, incorporating it by reference.
Source: simpleflying.com