Boeing, and FAA oversight
Yes, I am aware that Transport Canada will exercise their independence in re-evaluating the changed 737 MAX, rather than just accepting what the FAA and Boeing may present for acceptance. I'm also aware that Transport Canada's position was considered favourably by EASA and the Brazilian authority, who also were uneasy just accepting the FAA's certification.
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.
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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.
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Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.
STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.
STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns
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
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
What exactly do you mean with "compliant"? To the standard of the 1960ties of the 2020ties? Maybe the FAA simply wants to get out of the excessive grandfathering of the 737 family. The requirements for wiring have undergone multiple changes in the past decades, and B was able to evade them throughout the whole lifetime of the 737 through the grandfathering and - in the most recent times - the delegated power of certification. Time to make some substantial corrections.
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.
But as you pointed out - half the 737Max fleet already have CofA's and have been in service. If you are saying that he problem is so serious that those aircraft cannot fly because of it then by all logic that must also apply to all 737NG's. The only way I can see them getting around the issue of the 737NG fleet is to deem the 737Max a different type and so require certification under present day standards (which the wiring no longer meets).
However if they did decide that the 737Max was a completely new type and the present design did not meet todays standards then would Boeing have a financial claim for loses against the FAA, as the FAA have already approved the design albeit using their flawed approval process.
However if they did decide that the 737Max was a completely new type and the present design did not meet todays standards then would Boeing have a financial claim for loses against the FAA, as the FAA have already approved the design albeit using their flawed approval process.
My part of the World we would use a word corruption in that report.
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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.
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.
Last edited by ST Dog; 10th Mar 2020 at 18:52.
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?
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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 ?
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 ?
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.
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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.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
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.
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.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
I think the question was the case where one AoA sensor / SMYD was reporting a stall when the other was not.
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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.
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.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
No the FAA is retroactively deciding that the old grandfathering rules don't apply to a certain case (the wire separation) and make that unchanged item meet the new standards.
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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.
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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.
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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.
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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.
