It will be interesting to see what the ramifications are of the aircraft not being certified everywhere. Just for the record, there were a range of European types which in the past were not certified by the FAA, either because they had an unacceptable feature or because they were not even offered. The Caravelle for example was unacceptable to the FAA for US registration until some substantial modifications were made, while the VC-10, the Super One-Eleven and the Trident were never offered. These all operated into the USA even though they had not been certified there. US airlines like Alaska will have a real issue if their Max could not enter Canadian airspace.

The key may be insurance. My personal insurers stipulate I am only covered on a multi-engined aircraft operating under an AOC. They only have to add "and certified by worldwide authorities" and that's a real issue - bearing in mind the insurers are already on the hook for the two accidents.

I assume the wiring is for control of the trim.. And a wiring fault can result in two failure modes: Electrical trim not working, or Uncommanded trim runaway, maybe even preventing trim cut-out switches from working.
How is CFR25.671 to be affecting the certification of the MAX in light of the control forces in case of runaway, and the requirement of "without requiring exceptional piloting skill or strength" ?
If thehazard analysis of a fault in the electrical trim has changed from e.g. Minor to Hazardous, then this may also drive new requirements for probability of malfunction, fault detection, fault insulation, and redundancy in the manual trim.

only the NG's made after the rule should be affected.

Thanks 568 for this interesting information.
I emphasized some part of your response that ring a bell.
Last year when discussing the accidents I remember raising the issue of the difficulty of discerning whether one or both columns - and which one - was actively shaking in a stressful situation with lots of other alarms going off.
Can we conclude the mechanical interconnect might have rendered things difficult ?

What were the terms of the original means of compliance for the max?

If some items were grandfathered (based on earlier model experience ) then that should still stand.

OTOH if that was simply swept under the rug and the FAA bought in on a pig-in-the-poke, then tough luck to Boeing and they should have to pay the piper :)

The NG should have been compliant to the rules and the amendment levels negotiated, according to 21.101 the Changed Product Rule, and documented in the certification basis. It’s not just 1960’s vs 2000’s. Many rules have been amended over time since the original 737 certification. Generally, 21.101 requires that for the date of application, the certification basis is updated for all parts of the design that changed from the original. There are many nuances and exceptions, but that’s the gist of it. The new wiring rules may have been part of amendments that were issued after the NG certification, but prior to the application date of the MAX.

In my opinion, 21.101 itself as amended now is a practical mess, and is used with kid gloves with the applicant which find too many exceptions. 21.101 needs to be amended again, and simplified, in part to remove many provisions for exceptions and to shorten the life span of old regulation amendments. This would mean more new models, fewer derivatives, and more use of rules at the current amendment levels. Issuing this amendment would not get you on the Christmas card list of any OEM’s. But they had their chance to be “partners in safety” and opted to maximize share values instead.

The congress report said that safety concerns were raised within the FAA but overridden by more senior FAA officials. This may be one of the concerns.

My part of the World we would use a word corruption in that report.

Well the Max was already certified, over 300 had been delivered and were in service. The fault lies with the FAA for allowing Boeing to call the 737max a variant of an existing type and not a completely new type if it now wants to make it built to all modern specifications. If the FAA are now saying they made a mistake and allowed an aircraft built to incorrect standards to enter service then I would have thought that would open them up to a rather large legal liability.

My understanding was the same bundles were used on the MAX as the NG. No changes. Since they didn't change the wiring there was no reason to treat it as a new part of the deign. The point of grandfathering is that unchanged items stay unchanged. So as far a Boeing was concerned it didn't need to be evaluated under new rules. There are 100s (1000s?) of places on the NG and the MAX that wouldn't have meet the changed rules at the time of certification but were allowed because is wasn't a new part of the design.


Now the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and wants to make that unchanged item meet the new standards.

My understanding was that it was sensors used by the HGS, not the HGS as a whole.
The new (upgraded) sensors had not completed all the paperwork to allow installation on the 737.
All the testing was done, just not the paperwork exercise.

I haven't seen a good discussion about where that fell short. Did Collins say the new sensors were approved and someone just missed that it only for use with the HGS and not for the specific airframe? Did someone say that it was approved when it wasn't?

The MAX was built around the 737NG for certification purposes bar MCAS.
Having flown the NG (testing stalls) both pilots control columns will vibrate upon receipt of stall signals inputs from the hardware.

MAX should perform the same.

Yes, but understandably - now they know what a nose down hardover after TO leads to.
To solve this conundrum they should check older NG aircraft for wiring condition and chafing to create a data bank, from which they may conclude how the Max will fare.
This will either give confidence in the Max wiring or cause NG wiring to be modded.

There actually are cases where the new amendment is imposed regardless of product changes. I’m not a EE, but I think EWIS May have been a case of that.

I think the question was the case where one AoA sensor / SMYD was reporting a stall when the other was not.

Above you state that it is your understanding, then below you make a definitive statement.

I don’t think any of us know what small changes may or may not have been made to the trim system or related systems that would invoke the change product rule. There may have been some small changes made.

The location of the engines has changed. There is more chance of damage in the case of an uncontained failure.

This is not a changed product rule issue. The stab trim system had several changes for the Max, including changes to the motor, the motor control, the pilots' control switches, and MCAS. These changes, even without MCAS, required the system to be re-examined for compliance with the system safety analysis regulation (25.1309(b)). That rule is unchanged since the time of the NG certification in 1997. When you change the system, the whole system - not just the part you changed - has to be re-examined and found compliant because the system safety analysis regulations are system-level requirements. The wiring deficiencies should have been caught by a competently performed failure modes and effects analysis, as would the effects of a failed high out of range AOA sensor. The EWIS requirements in 25.1707 introduced in 2007 are a red-herring in this case. While that rule is more prescriptive, 25.1309(b) effectively imposed the same requirement for adequate wire separation to prevent catastrophic events from wiring faults, and that requirement was identical for both the NG and Max programs.

So, what you say is that - if the FAA is correctly trying to get back control over the certification, and the wiring is found to be changed based on the findings - the wiring in all NG's would need to be changed as well?

See, the NG has been flying since mid of 90ies. If they had changed anything to the stab trim of the NG after 2007 they would have had to fulfill that requirement for the newly produced aircraft. I don't think they have though.

The system was changed for the Max, so the wiring should have been part of the new stab trim system safety analysis for the Max. It either wasn't examined or the issue was missed. At this point, because the design was already approved and the FAA did not revoke the type certificate, what's driving the FAA is apparently a determination that an unsafe condition exists warranting corrective action under 14 CFR part 39 (the part under which airworthiness directives are issued). To address the issue, Boeing has to propose a design change. That design change is required by 14 CFR part 21 to comply with the airworthiness requirements, including 25.1309 and 25.1707. A TC holder can't obtain approval of a non-compliant design change other than via an exemption. You can bet the FAA won't be issuing any exemptions from the system safety requirements for the stab trim system.

If the lack of wire separation and the consequences of that lack of separation are similar for the NG, you would normally expect a similar finding that an unsafe condition warranting AD action exists on those airplanes as well. However, at this point top FAA management is likely making the decisions rather than staff engineers following the normal processes, so it's hard to predict what the FAA will decide for the NG wiring. The normal FAA process would call for an AD if the wiring is found to have the potential for a single fault condition to be catastrophic. The Boeing lobbying will likely be based on a probability argument.