Recently FAA (Federal Aviation Administration) published AD 2020-18-12. This AD (Airworthiness Directive) is effective for certain Boeing 777, line numbers 1 thru 561 aircraft having a "wet" (containing fuel) wing centre section. Some 777's have dry wing centre sections but most have a fuel containing wing centre section. These affected aircraft are over 20 years old.
Exempt are aircraft equipped with "Flammability Reduction Means (FRM)" which are generally in the form of a nitrogen generation fuel tank inerting system.
The AD addresses a potentially unsafe condition, consisting of ignition sources in the centre wing tank, originating from a fault in the fuel quantity indication system.
The AD stipulates actions that mitigate this ignition risk "using a method approved in accordance with the procedures specified in paragraph (i) of this AD".
Paragraph (i) of the AD describes the application of an AMOC (alternate means of compliance) to the AD.
In other words, there is no approved means of compliance available at this time and the AD leaves it up to the Seattle ACO (Aircraft Certification Office) to approve compliance on an individual basis. Applicants may be Boeing or an independent Part 21 approved design organisation that could develop a method of compliance.
It is highly unusual for any authority to publish an AD without a specified mitigation of a potentially unsafe condition. The only cases known in recent history are the grounding of the Boeing 787, due to Lithium Ion battery safety concerns and the Boeing 737 MAX flight control issues.
Normally a regular AD publication is preceded by the issue of an NPRM (Notice of Proposed Rule Making), to which parties can provide consultation. This AD was no different and comments of many parties are indicated in the supplementary information section (highlighted in attached document).
Boeing, and (presumably) EASA requested FAA to withdraw the NPRM arguing that no unsafe condition exists or has already been mitigated by the SFAR 88 drive that resulted in many fuel tank safety mandatory modifications and maintenance practices (for all aircraft types).
Boeing argued that:
"Boeing stated that because it considered the use of FRM (NGS) to address unknown ignition sources as the final corrective action, Boeing has not developed center tank FQIS wire separation service instructions for passenger aircraft. Boeing stated that it believes no unsafe condition exists and does not feel that the lack of FRM rule harmonization should cause additional work and expense for airlines."
Airlines such as Emirates, Cathay Pacific, Singapore Airlines and KLM requested to withdraw the NPRM, arguing that the stipulated open ended means of compliance is unjustified by the perceived risk.
All of the above arguments have been disagreed with by FAA and they went ahead with publishing the final rule.
There have been a couple more arguments with Boeing about the cost/benefit of the implications of this AD which I will not comment on here.
Here is what EASA argues:
"EASA is not in possession of sufficient data to allow determination of an unsafe condition and to support corrective action that would be deemed proportionate to the risk. Consequently, there is insufficient justification to warrant the actions as required by FAA AD 2020-18-12."
This is a bold statement and perhaps a tell tale in regulatory affairs. EASA carries their own Boeing 777 Type Certificate and, as such, should have access to the same fleet safety data as FAA. In the bilateral procedures (indicated in the bilateral TIP between FAA and EASA) it is stated that both authorities rely on each other as "state of design" for different aircraft types to regulate the level of safety of the applicable type certificates to acceptable levels.
The fact that EASA does not adopt a rule based on the same safety data that made FAA issue the AD indicates a break with the concept of reciprocity in data acceptance.
On the unrelated issue of EASA's decision to, independently (from FAA), conduct their own certification test flights verification of the Boeing 737-MAX, also hints to a break in acceptance of FAA data and its judgement.
The fact that there is politics involved in those decisions can not be denied.
But when a agency defies the opinion and judgement of many industry safety experts and a major international safety agency under political pressure, perhaps it defies its own purpose.
We can only hope that the cooperation and harmonisation of rules and regulations that have been established over many years (and has been beneficial to aviation) will continue to exist and progress.
Attached AD 2020-18-12 containing the comments to the NPRM and EASA's explanatory note for not adopting the AD.