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Boeing, and FAA oversight

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Boeing, and FAA oversight

Old 8th Mar 2020, 23:21
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This disagreement probably stems from the proposed MCAS modification.

With a dual system (pre mod) where each stick is independently associated with an AoA input, it should be possible to inhibit one side without loss of function.
In the initial situation the crew do not know if the stick-shake is valid or false, ie. which vane is inaccurate. After crosschecking airspeed for stall conditions it should be possible to identify and inhibit the faulty side, which should leave the unaffected side to provide any subsequent alert.
The crew can operate without distraction and still retain the stall alerting function.

However, if the MCAS modification 'cross-wires' the stick-shake functions as a result of having to use both FGCs and both AoA inputs for MCAS fault detection, then identification of a faulty stick-shake is more difficult, and inhibiting one side may also affect all stall alerting.
The debate then is to what degree is the shaker distracting vs the loss of stall alerting. It might be possible to retain one stick so that a subsequent valid stall would add shake the errant system so that the cumulative, change in alerting is recognisable.
A further complication in the Max is that AoA input to the ADC provides speed (and alt) corrections. There will be a difference in airspeed with erroneous AoA input or failure, but comparing with the standby ASI it should be possible to identify a faulty system. However, if by inhibiting one AoA this also affects both ADC (as per FGC hypothesis above) then both EFIS airspeed display will have an error. Thus the debate to inhibit AoA or not must additionally consider inaccurate speed together with with distraction.
The options are further complicated if shake can be inhibited independently of AoA, but if inhibited which system is the valid one ?
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Old 8th Mar 2020, 23:26
  #322 (permalink)  
 
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WSJ

https://www.wsj.com/articles/faa-poi...in-11583704341
FAA Poised to Require Electrical Wiring Fixes Before Boeing 737 MAX Jets Can Fly Again
Agency expected to mandate rerouting of certain wires to comply with longstanding safety regulations

By Andy Pasztor and Andrew Tangel
Updated March 8, 2020 6:48 pm ET

U.S. air-safety regulators are poised to order electrical wires relocated inside Boeing Co. BA 0.75% 737 MAX jets in the latest complication and potential delay for their return to commercial service, according to people briefed on the deliberations.

The preliminary decision, which hasn’t been reported before, covers all of the nearly 800 MAX airliners produced so far. The decision could be affected by further internal discussions and additional data the plane maker may submit to the regulator.

But in the past few weeks, these people said, Federal Aviation Administration managers and engineers have concluded that the potentially hazardous layout violates wiring-safety standards intended to prevent dangerous short-circuits.

Under extreme circumstances, wiring failures could cause flight-control systems to sharply point down an aircraft’s nose in a similar way to the automated maneuvers that brought down two MAX jets and claimed 346 lives.

The Chicago plane maker, according to people briefed on the details, has argued that the current wiring design meets FAA and international safety standards. Boeing also has told the FAA that because the risks are so remote—and such a relatively small number of similar short-circuits have occurred during the extensive history of the MAX’s predecessor model—no wiring redesign is necessary.

The emerging agency view, however, is based on longstanding regulations put in place following electrical fires and fuel-tank explosions on commercial jets over decades.

The FAA’s move caps several months of behind-the-scenes maneuvering between Boeing and the FAA that already has delayed crucial flights needed to vet fixes to MAX flight-control software and move forward with certifying the grounded jets as safe to carry passengers again.

Complications stemming from mandatory wiring changes could delay FAA directives ungrounding the beleaguered fleet for at least several weeks, some of the people said, potentially beyond the mid-June timeline previously projected by industry and government officials.

The wiring concerns also have turned into a test case of what Dave Calhoun, Boeing new chief executive, has touted as his more realistic and conciliatory approach toward FAA safety demands before allowing the MAX fleet back in the air.

The FAA said on Sunday that it continues to engage with Boeing on the wiring issue and the MAX will return to service only after the FAA is satisfied that all safety-related issues are addressed.

A Boeing spokesman said that discussions with the FAA continue, but regardless of the outcome the company’s estimate for a midyear return to service is unchanged.

If Boeing continues to press its case in the face of the FAA’s preliminary decision, one of the people briefed on the deliberations said, the likely upshot would be months of additional debate involving the FAA and foreign regulators in Europe, Canada and Brazil.

That is a major reason Boeing, which already has been devising ways to relocate certain wiring, ultimately is likely to accept the FAA’s position. And from a public perception standpoint, the people said, U.S. authorities are loath to break with demands from foreign regulators that wiring fixes must be completed before the fleet is allowed to resume operations.

Canadian regulators haven’t taken an official position yet on how Boeing should mitigate any risks associated with the wire bundles, said Nicholas Robinson, Transport Canada’s director general of civil aviation. But privately, according to people familiar with the details, Canada strongly supports relocating some wires.

“We’ve expressed our concerns to the FAA,” Mr. Robinson said in an interview at an aviation event in Washington, D.C., last week. “We’ll look at the FAA’s solution,” he added, “and then we’ll evaluate if that meets our needs.”

The planes have been grounded since March 2019, prompting a production shutdown, the biggest corporate crisis in Boeing’s history and severe disruptions to the global airline industry.

Industry and government safety experts have said the wiring issues should have been identified and resolved during the initial certification of the MAX. The stricter safety standards for wiring didn’t apply to earlier 737 models.

Among major questions that still need to be answered, according to these experts, is precisely how and when wiring will be redone on aircraft which operated before the grounding. Looking forward, Boeing has agreed to make wiring design changes once the assembly line revs up again.

The wiring debate follows a long string of setbacks and hurdles for Boeing regarding recertification of the 737 MAX, including a recent FAA directive proposing mandatory inspections and fixes to a metallic lining that serves as a shield against lightning strikes for engine-control wiring.

Before the FAA will authorize resumption of passenger operations, MAX jets also will be subjected to checks of fuel tanks for debris, along with verification of mandatory inspections, maintenance procedures and operational readiness flights. Unlike past FAA procedures, agency officials won’t delegate signoff authority to Boeing to ensure MAX jets are airworthy and ready for airline operations.

Write to Andy Pasztor at [email protected] and Andrew Tangel at [email protected]
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Old 8th Mar 2020, 23:36
  #323 (permalink)  
 
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Originally Posted by safetypee
This disagreement probably stems from the proposed MCAS modification.

With a dual system (pre mod) where each stick is independently associated with an AoA input, it should be possible to inhibit one side without loss of function.
In the initial situation the crew do not know if the stick-shake is valid or false, ie. which vane is inaccurate. After crosschecking airspeed for stall conditions it should be possible to identify and inhibit the faulty side, which should leave the unaffected side to provide any subsequent alert.
The crew can operate without distraction and still retain the stall alerting function.

However, if the MCAS modification 'cross-wires' the stick-shake functions as a result of having to use both FGCs and both AoA inputs for MCAS fault detection, then identification of a faulty stick-shake is more difficult, and inhibiting one side may also affect all stall alerting.
The debate then is to what degree is the shaker distracting vs the loss of stall alerting. It might be possible to retain one stick so that a subsequent valid stall would add shake the errant system so that the cumulative, change in alerting is recognisable.
A further complication in the Max is that AoA input to the ADC provides speed (and alt) corrections. There will be a difference in airspeed with erroneous AoA input or failure, but comparing with the standby ASI it should be possible to identify a faulty system. However, if by inhibiting one AoA this also affects both ADC (as per FGC hypothesis above) then both EFIS airspeed display will have an error. Thus the debate to inhibit AoA or not must additionally consider inaccurate speed together with with distraction.
The options are further complicated if shake can be inhibited independently of AoA, but if inhibited which system is the valid one ?
I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly. Earlier I wondered how the FGCs used the two inputs and was surprised to see they are bypassed to operate those alarms directly. Perhaps I misread it, but it makes a great deal of sense to push that function as early in the sensor chain as possible to decrease the number of links and the ability to fail.

I do agree that figuring out the desired failure handling is not easy. It has to be one that sorts false inputs from true inputs and tells the pilots what has gone wrong. Still it's been possible to shut down the remaining operating engine when the stress levels get too high, so it's clear that solving this general problem is not easy.

What is clear is that the outcome possible under the previous version will never happen again; that is, there won't be a chance that under an AoA disagree situation that an MCAS or, possibly, even STS correction to trim will be allowed. So now it's shifted to the more esoteric argument about how to automate proper handling of false information that looks exactly like true information. Anyone who comes to the certain solution for that problem will clean up in the stock market.
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Old 9th Mar 2020, 00:30
  #324 (permalink)  
 
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Originally Posted by A4
Not in FBW Airbus you won’t........side stick has identical resistance at 0 knots or 500 knots.

A4
Which is one of the reasons that I believe the original Canadian suggestion of simply getting rid of MCAS altogether and training for the non-linearity in the stick forces at some ends of the envelope was a proper approach to much of the problem.

Unless MCAS was needed for more than stick force linearity issues, of course...something we still don't know for sure.
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Old 9th Mar 2020, 02:25
  #325 (permalink)  
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Originally Posted by MechEngr
I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly. Earlier I wondered how the FGCs used the two inputs and was surprised to see they are bypassed to operate those alarms directly. Perhaps I misread it, but it makes a great deal of sense to push that function as early in the sensor chain as possible to decrease the number of links and the ability to fail.

I do agree that figuring out the desired failure handling is not easy. It has to be one that sorts false inputs from true inputs and tells the pilots what has gone wrong. Still it's been possible to shut down the remaining operating engine when the stress levels get too high, so it's clear that solving this general problem is not easy.

What is clear is that the outcome possible under the previous version will never happen again; that is, there won't be a chance that under an AoA disagree situation that an MCAS or, possibly, even STS correction to trim will be allowed. So now it's shifted to the more esoteric argument about how to automate proper handling of false information that looks exactly like true information. Anyone who comes to the certain solution for that problem will clean up in the stock market.
Your quote "I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly".

Your information is incorrect:

Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. 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
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Old 9th Mar 2020, 04:14
  #326 (permalink)  
 
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Originally Posted by A4
Not in FBW Airbus you won’t........side stick has identical resistance at 0 knots or 500 knots.

A4
And unwinding the aerodynamic load on a stab using the manual trim wheel (such as a "trim runaway") at 400 knots has what to do with a non-FBW aircraft?
Whats it like in direct law in such a situation? Aerodynamic air loads skip the Airbus do they?
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Old 9th Mar 2020, 06:04
  #327 (permalink)  
 
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Originally Posted by 568
Your quote "I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly".

Your information is incorrect:

Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. 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
Good. I was correct that it wasn't the FGCs, which was the main point, that the software BA is generating is not controlling the stall warnings.
Thanks for the correction, but it's the same outcome as far as STS and MCAS software is concerned.
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Old 9th Mar 2020, 06:08
  #328 (permalink)  
 
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Originally Posted by RubberDogPoop
And unwinding the aerodynamic load on a stab using the manual trim wheel (such as a "trim runaway") at 400 knots has what to do with a non-FBW aircraft?
Whats it like in direct law in such a situation? Aerodynamic air loads skip the Airbus do they?
I believe Airbus uses an electrohydraulic system to connect what look like fake trim wheels. I cannot tell if they are complete wheels or just an arc exposed above the console, but they provide no force feedback to the actual loads on the horizontal stabilizer and no way to put a full grip on them. It looked to me like their function could be handled with a paddle switch.
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Old 9th Mar 2020, 07:19
  #329 (permalink)  
 
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Originally Posted by MechEngr
I believe Airbus uses an electrohydraulic system to connect what look like fake trim wheels. I cannot tell if they are complete wheels or just an arc exposed above the console, but they provide no force feedback to the actual loads on the horizontal stabilizer and no way to put a full grip on them. It looked to me like their function could be handled with a paddle switch.
Wrong again On the A320-330-340 they are full wheels that are mechanically connected to the trim actuator and turn when the stab moves.
They are in fact a final backup for longitudinal control should all electrics fail. Still need hydraulics though, like the 747 and all later Boeings - the 737-o-saurus must be the only airliner of any size still flying with a direct mechanical connection to the THS. On the A350-380 they're gone completely and replaced by switches.
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Old 9th Mar 2020, 07:27
  #330 (permalink)  
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Airbus only goes into Direct Law when the gear goes down (apart from triple ADR Fault). In Alternate Law, longitudinal trim is still controlled by the FBW system - it remains very stable and easy to fly. More sensitive in role as it in now roll direct as opposed to roll rate.

The issue of pitch/thrust couple only occurs in direct law (gear down) as auto trim deals with this even in Alternate Law. There is Mechanical Back up “Law” which is a direct link between trim wheel to THS actuators (wheel NOT affected by aerodynamic load) but this is purely designed for used whilst you recover one of the 5 flight control computers (3 x SEC , 2 xELAC). I believe Airbus test pilots have landed the aircraft in mechanical back-up.

Anyway, my original post was purely to clarify that there is zero aerodynamic load effect in Airbus Side stick. What's the deal with 777/787 FBW control columns? Do they have artificial load feel?

A4

Typing at same time as Fizz57.....
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Old 9th Mar 2020, 07:43
  #331 (permalink)  
 
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MechEng, 586,
Thanks for the clarification. A key aspect is the independence of each of the combined stall alerting (shaker) and stall ident (push) systems.

Prior to the mod, any one side could fail / be inhibited without loss of stall alerting / warning; - dual certification safety case.

The question post MCAS mod is if there is a situation where crew action (cbs), or reconfigured use of AoA (routing to SMYD), will result in the loss of both stall systems.

Thus the different opinions range between:-
- Continued flight with distracting alerts; stick shake and other alerting annunciation, and incorrect speed information, EFIS speed error and low speed awareness with differences between crews displays.
- Loss of all stall alerting with single AoA failure.

Either option could invalidate the previous safety case for stall protection. If so then Boeing could request an alleviation from the requirement - a reduced level of safety (stall alerting) after MCAS modification (AoA failure case) - debatable amongst regulators and not confidence promoting for the 737 Max.

Alternatively, that either or both Boeing and the FAA did not identify this weakness in their latest safety assessments; significantly embarrassing for reputations, even more so if Canada identified the issue because of previous grounding history.

Last edited by safetypee; 9th Mar 2020 at 08:39.
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Old 9th Mar 2020, 11:43
  #332 (permalink)  
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“We’ve expressed our concerns to the FAA,” Mr. Robinson said in an interview at an aviation event in Washington, D.C., last week. “We’ll look at the FAA’s solution,” he added, “and then we’ll evaluate if that meets our needs.”
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.
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Old 9th Mar 2020, 13:04
  #333 (permalink)  
 
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Originally Posted by fizz57
Wrong again On the A320-330-340 they are full wheels that are mechanically connected to the trim actuator and turn when the stab moves.
They are in fact a final backup for longitudinal control should all electrics fail. Still need hydraulics though, like the 747 and all later Boeings - the 737-o-saurus must be the only airliner of any size still flying with a direct mechanical connection to the THS. On the A350-380 they're gone completely and replaced by switches.
Ok, but they are moving hydraulic valves via a cable and not moving the surface directly so there is no force feedback for the amount of trim discrepancy. That has to be a low-friction system, otherwise it will detect a problem and report as a jammed stabilizer.

Can the system decouple the THS actuator from the trim wheel input in the case the cable becomes jammed and not the stabilizer?
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Old 9th Mar 2020, 14:41
  #334 (permalink)  
 
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Boeing shares plunge as FAA rejects proposal on MAX wiring

(Reuters) - Shares of Boeing Co <BA.N> dropped 12% on Monday after the planemaker's proposal to leave wiring bundles in place on the grounded 737 MAX failed to get the backing of U.S. aviation regulators, potentially delaying the plane's return to service.

Source
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Old 9th Mar 2020, 15:39
  #335 (permalink)  
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Originally Posted by MechEngr
Good. I was correct that it wasn't the FGCs, which was the main point, that the software BA is generating is not controlling the stall warnings.
Thanks for the correction, but it's the same outcome as far as STS and MCAS software is concerned.
No problem.
The new software update may prove to be unstable because of old memory architecture and data bus transfer.
I know there are folks on this forum with much more expertise on this subject than I could ever imagine.
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Old 9th Mar 2020, 15:45
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Not sure what to think of this. If this is purely about safety and the wiring routing is deemed unsafe then its going to be just as unsafe in the 737NG as well as the 737Max, if that is the case then why are they not grounding the 737NG fleet.

Or is the FAA just overreacting after their recent failures in supervision on the 737Max program?
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Old 9th Mar 2020, 15:53
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cashash part of it may be overreaction (political) but there is also the issue that more than half of the grounded Maxs never entered airline service and may not have C of As. The continuing airworthiness requirements, in terms of safety assessments, are different for a newly built aircraft and an inservice aircraft - you can take time to fix an inservice issue (or never fix it at all, if deemed safe to take that route) but you have to fix many more such issues at CofA. (Both from a regulatory point of view and a commercial one - new customers don't like accepting aircraft with potential ADs etc hanging over them)
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Old 9th Mar 2020, 15:58
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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.
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Old 9th Mar 2020, 16:17
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The wiring was compliant when the NG was certified wasn't it? It wasn't when the Max was certified. Thats the difference.It may be safe as is, but it doesn't meet the requirements, Boeing should have known this and not cut corners, but well, Boeing.
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Old 9th Mar 2020, 16:43
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Originally Posted by Ben_S
The wiring was compliant when the NG was certified wasn't it? It wasn't when the Max was certified. Thats the difference.It may be safe as is, but it doesn't meet the requirements, Boeing should have known this and not cut corners, but well, Boeing.
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.
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