Boeing - Design Issues...

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Vigilant1

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The plane was not airworthy according to the report. It had a defective or improperly calibrated AOA sensor that caused a flight control malfunction.
The standard definition of airworthy is compliance with the Type Certificate and other standards and in a condition for safe operation.
A report issued yesterday indicated the shop in Miami that worked on that AoA sensor has now been sanctioned by the FAA ( for doing work/selling products that they weren't qualified/authorized by the FAA to sell). "Cockroach corner" indeed. I hope someone goes to jail, and I hope the hire a few investigators to find and close down similar shops wherever they are.
Still, a faulty AoA sender shouldn't (and needn't) produce this result.
 
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davidb

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The plane was not airworthy according to the report. It had a defective or improperly calibrated AOA sensor that caused a flight control malfunction.
The standard definition of airworthy is compliance with the Type Certificate and other standards and in a condition for safe operation.
I meant the the model in general is an airworthy design. The condition of the specific Lion Air plane isn’t relevant to the point I was trying to make. A bird strike to the AoA vane at rotation could effect the same indications.
 

BBerson

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The report said the Miami company (Xtra) was qualified/authorized by the Miami FAA FSDO. Might have been an error or untrained technician. But yes a single part failure should never cause the plane to go out of control.
That is a certification error. Plenty of blame to spread among the manufacturer, the certification authority, the new AOA part made by Collins that failed, the repaired part supplied by Xtra that was improperly calibrated, the maintenance engineers at Lion Air, the distracting controllers and lastly the pilots (including the surviving pilots that didn't report defects properly).
 

bmcj

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But yes a single part failure should never cause the plane to go out of control.
That is not quite correct.... a wing falling off would definitely cause the plane to go down (except, evidently, the F-15), but that is not justification to ground the design, or else all aircraft would be grounded. The goal of the design is to provide redundancy and error checking, or to mitigate the major effects of a failure by other means such as alternate backup equipment or standardized set procedures. On major non-redundant items like wings, they engineer a large factor of safety to help make sure they don’t fall off.

I know this point is obvious to everyone, but it does provide some perspective regarding the failed device and where it ranks in importance and criticality.
 
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BBerson

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A wing is "fail safe". That means the certification standards require multiple load paths so a single failure will not cause a wing to fall off between inspections.
If you read the report, it said MCAS would continue to override the first officers attempt to fly with control yoke. But not the captains controls. Very disturbing.
 
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bmcj

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A wing is "fail safe". That means the certification standards require multiple load paths so a single failure will not cause a wing to fall off between inspections.
Not making a point here, just throwing in a twist (one example of many): ;)

 

Toobuilder

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Not to be pedantic here, but loss of the single AoA vane does not result in the airplane "going out of control" if the pilots do the right thing following failure. There are plenty of light piston twins (for example) that are marginally controllable on a single engine even if the pilot is "perfect", - and deadly of he's off his game just a bit - yet these are all certified for public consumption.
 

bmcj

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Not to be pedantic here, but loss of the single AoA vane does not result in the airplane "going out of control"
Exactly!!! If anyone wants to argue that fact, ask them how many planes they’ve flown and landed successfully that don’t even have an AOA sensor.
 

Himat

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We need to see the next investigation and final report on the second crash. This one has so many factors, some of which seem ignored in the recommendations. The second one will probably help in establishing the best way to enhance safety.
Maybe, maybe not.

I do think the enhancements to safety suggested will be piecemeal. A little on the training, a little on the design and a little on the regulations and enforcement of those. I do not think there will be a ground up rethink of the way’s things are done.

Like the requirement for force feedback to the stick, stick shaker, MACS and other add on to make a modern airline feel like an old all mechanical airplane to the pilot. To me it looks like that is a strategy that now is exhausted.

The safe way may as well skip all that and require a fly by wire system. Then devote the resources to set the requirement to make a fly by wire system safe. By all parties; regulatory, design, production, operation and maintenance.
 

davidb

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If you read the report, it said MCAS would continue to override the first officers attempt to fly with control yoke. But not the captains controls. Very disturbing.
The controls are mechanically connected and the trim switches on either side perform the same function. The first officer’s inputs were the difference noted. Unlike the captain, the first officer only thumbed the switch for a second, enough to temporarily stop the nose down trimming, but he didn’t hold the switch for the several seconds needed to return it to a trimmed condition. That was the fatal difference.

A glaring omission in the analysis is the physical position of the control column. The report noted the 100+ pounds of control force applied but I wonder how much more aft column movement was available. I’m told there is enough elevator authority to overcome full nose down trim but that is probably only true in a normal speed regime.

The transcript has the first officer comment indicating the nose down force as heavy. One would expect a a robust effort to trim nose up but the data doesn’t show him holding the thumb switch for up trim nor does it indicate he was pulling the column back with all the force he could muster given the dire situation of impending impact.

The second crash report preliminary leaks seems to indicate the panic we would expect of a crew that had no more up pull available but they accelerated beyond red line before the fatal dive.
 

davidb

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Maybe, maybe not.

I do think the enhancements to safety suggested will be piecemeal. A little on the training, a little on the design and a little on the regulations and enforcement of those. I do not think there will be a ground up rethink of the way’s things are done.

Like the requirement for force feedback to the stick, stick shaker, MACS and other add on to make a modern airline feel like an old all mechanical airplane to the pilot. To me it looks like that is a strategy that now is exhausted.

The safe way may as well skip all that and require a fly by wire system. Then devote the resources to set the requirement to make a fly by wire system safe. By all parties; regulatory, design, production, operation and maintenance.
I have flown the A320 for twelve years and now have flown the B737 for a total of eleven years. I like both. I don’t think the AirBus is safer. I think they are both safe but very different in their methods.

Your critique of the B737 evolution is shared by many. I can only offer my opinion, also shared by many, that the Max is the best handling version of any model of 737.

If things were to go wrong beyond what my training could handle or what engineers could predict, I’d prefer to be in the 737. There’s something comforting about knowing there’s still some cables and pulleys should everything else fail.
 

BBerson

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Unlike the captain, the first officer only thumbed the switch for a second, enough to temporarily stop the nose down trimming, but he didn’t hold the switch for the several seconds needed to return it to a trimmed condition. That was the fatal difference.
If you read page 50 of the report it said the first officers thumb switch is inhibited when MCAS is activated. :eek:

Page 50:
MAX, two column cutout switching modules, one for each control column, are actuated when the control columns are pushed or pulled away from zero (hands off) column position. When actuated, the column cutout switching modules interrupt the electrical signals to the stabilizer trim motor that are in opposition to the elevator command.

The MCAS function requires the stabilizer to move nose down in opposition to the column commands when approaching high angles of attack. To accommodate MCAS, the column cutout function in the first officer’s switching module was modified to inhibit the aft column cutout switch while MCAS is active, allowing aircraft nose-down (AND) stabilizer motion with aircraft nose-up (ANU) column input. Once MCAS is no longer active, the normal column cutout function in the stabilizer nose down direction is re-instated.
 

davidb

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The report said the Miami company (Xtra) was qualified/authorized by the Miami FAA FSDO. Might have been an error or untrained technician. But yes a single part failure should never cause the plane to go out of control.
That is a certification error. Plenty of blame to spread among the manufacturer, the certification authority, the new AOA part made by Collins that failed, the repaired part supplied by Xtra that was improperly calibrated, the maintenance engineers at Lion Air, the distracting controllers and lastly the pilots (including the surviving pilots that didn't report defects properly).
Yes, plenty to blame or contributing factors leading up to this airplane getting airborne with a bad AoA/stick shaker. All of that gets mitigated or could have prevented this crash had there been a checklist for stick shaker. The idea actually dawned on me when I was envisioning all the ensuing banter and reading how the lack of AoA disagreement warning was a contributing factor. The last thing this crew needed was another warning. Some of the warnings were minor and caused by them touching down briefly after liftoff, unrelated to AoA.

What this crew needed (any crew) was the knowledge of what to do initially with stick shaker on takeoff and then a single checklist that could walk them through all the ensuing considerations. We can discuss all factors of this crash until we puke but the existence of that checklist would have prevented this crash and will prevent a future crash of similar circumstances. I would like to hear arguments against my position. Am I missing something?
 

davidb

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If you read page 50 of the report it said the first officers thumb switch is inhibited when MCAS is activated. :eek:

Page 50:
MAX, two column cutout switching modules, one for each control column, are actuated when the control columns are pushed or pulled away from zero (hands off) column position. When actuated, the column cutout switching modules interrupt the electrical signals to the stabilizer trim motor that are in opposition to the elevator command.

The MCAS function requires the stabilizer to move nose down in opposition to the column commands when approaching high angles of attack. To accommodate MCAS, the column cutout function in the first officer’s switching module was modified to inhibit the aft column cutout switch while MCAS is active, allowing aircraft nose-down (AND) stabilizer motion with aircraft nose-up (ANU) column input. Once MCAS is no longer active, the normal column cutout function in the stabilizer nose down direction is re-instated.
The switching module that was modified is not the “first officer’s” it’s the control column module. The control column is mechanically connected. It knows not which pilot is moving the control column.

Normally, any electric trim input opposite the movement of the column is inhibited. If you’re pulling up, you can’t trim down and vice versa. That feature was inhibited on the Max only when MCAS is active. The reason being if you got into an unusually high pitch attitude you might be still pulling back but you need nose down trim. Yeah, I’m probably missing something in the logic of that too. Anyway, that nose down trimming still can be stopped by actuating the thumb switch up, just not by moving the control column aft.

The control column is the vertical pole the yoke is attached to. Perhaps the terms are confusing the issue descriptions. Pulling on the “yoke” or “stick” stops down trim unless MCAS is active. Only thumbing up trim switches or turning off the cutout switches stops MCAS nose down trimming. Well, grabbing the trim wheel stops it too.
 

davidb

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Did you see my post 372?
If I was a Max pilot I think I would be shocked and angered to read that about MCAS.
I’m only mildly annoyed at the misleading “first officer’s” reference in the report. I am (was?) a Max pilot and fully understood all available information on MCAS within a week of the first crash. The report doesn’t contain any systems information I don’t already know. I know I have ultimate control over MCAS. I was never shocked or angered over MCAS. I have always agreed with Boeing’s original assessment of a pilot’s need for information and that I would know what to do without specific knowledge. However, I do respect the differing opinions of my peers and do agree something needs changing.
 

BBerson

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The way I understand that description of MCAS is that it "inhibits" one or both pilots ability to thumb in up trim to stop the dive.
That would be the cause of the crash in my opinion.

I assumed you had no knowledge of MCAS before the crash.
 

davidb

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The way I understand that description of MCAS is that it "inhibits" one or both pilots ability to thumb in up trim to stop the dive.
That would be the cause of the crash in my opinion.
It does not do as you understand. It does as it was doing for twentysome times while the captain was flying. The first officer could have done the same thing with his thumb switch. He didn’t. He only held the switch for one second each time. He never held it long enough to roll it back to a trimmed condition like the captain was doing.
 
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