Ethiopian airliner down in Africa
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Speculatively with both pilots hauling back on the control column and no electric trim, the moment any of them lets go to give the wheel a try the nose would dip down again. Additionally, at nose low and high speed with stab overloaded the wheel might have been much too stiff to both move and do so enough times to make an impact.
I hate to speculate on this but it points to proper action by crew finding themselves unable to bring nose up with manual means and reactivating the cutouts to regain electric trim capability. (Which should come back and if used should stop MCAS either way, unless...)
I hate to speculate on this but it points to proper action by crew finding themselves unable to bring nose up with manual means and reactivating the cutouts to regain electric trim capability. (Which should come back and if used should stop MCAS either way, unless...)
No, well spotted, I’m not a pilot, but I assume that not every control in a simulator for an aircraft where the force felt through the controls relates to the forces the control surfaces they connect to are experiencing [i.e. a non-fully-FBW plane] will be 100% accurate?
The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.
The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
With runaway stab you can’t catch it by trimming - it is running away...
With MCAS unwanted (for want of a better description) operation you can theoretically catch (reverse) it by trimming.
Another difference is that in an AoA fault caused unwanted MCAS operation other factors also come into play - even before MCAS operation on flap retraction:
Autothrottle, Instrument anomaly, Stall warning etc. which can cause:
Unwanted rise in speed, initial pilot input nose down response, cockpit confusion.
Therefore the standard drill for stab runaway does not necessarily apply. Trimming to neutral and ATS disconnect might well have priority over stab trim cutoff operation.
Of course we didn’t know this, the poor crews didn’t know it and it is a scenario which Boeing will be looking at hard before submitting a suitable procedure for recertification, I am sure.
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[QUOTE=bill fly;10438384]
The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.
The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.[/QOTE]
And that highlights a big difference between runaway stab. and MCAS unwanted operation:
With runaway stab you can’t catch it by trimming - it is running away...
With MCAS unwanted (for want of a better description) operation you can theoretically catch (reverse) it by trimming.
Another difference is that in an AoA fault caused unwanted MCAS operation other factors also come into play - even before MCAS operation on flap retraction:
Autothrottle, Instrument anomaly, Stall warning etc. which can cause:
Unwanted rise in speed, initial pilot input nose down response, cockpit confusion.
Therefore the standard drill for stab runaway does not necessarily apply. Trimming to neutral and ATS disconnect might well have priority over stab trim cutoff operation.
Of course we didn’t know this, the poor crews didn’t know it and it is a scenario which Boeing will be looking at hard before submitting a suitable procedure for recertification, I am sure.
You are both right. But Boing introduced a very "clever" sentence in the AD:
"Electric estabilizer trim can be used to neutralize control column pitch forces before moving the stab trim cutout switches to cutout"
Can: means that if you do it and you crash, they would say they didn't tell you to do it, but if you don't do it and you crash they will say that they mentioned it for something.
Not that any amount of words is going to change the fact that they are responsible. If only they were as clever in the design as they are with legal-related documents.
The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.
The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
And that highlights a big difference between runaway stab. and MCAS unwanted operation:
With runaway stab you can’t catch it by trimming - it is running away...
With MCAS unwanted (for want of a better description) operation you can theoretically catch (reverse) it by trimming.
Another difference is that in an AoA fault caused unwanted MCAS operation other factors also come into play - even before MCAS operation on flap retraction:
Autothrottle, Instrument anomaly, Stall warning etc. which can cause:
Unwanted rise in speed, initial pilot input nose down response, cockpit confusion.
Therefore the standard drill for stab runaway does not necessarily apply. Trimming to neutral and ATS disconnect might well have priority over stab trim cutoff operation.
Of course we didn’t know this, the poor crews didn’t know it and it is a scenario which Boeing will be looking at hard before submitting a suitable procedure for recertification, I am sure.
"Electric estabilizer trim can be used to neutralize control column pitch forces before moving the stab trim cutout switches to cutout"
Can: means that if you do it and you crash, they would say they didn't tell you to do it, but if you don't do it and you crash they will say that they mentioned it for something.
Not that any amount of words is going to change the fact that they are responsible. If only they were as clever in the design as they are with legal-related documents.
They should've kept airframe and hydraulics (99% of them, just a touch here and there)
Nearly 25 years ago Airbus complained to JAA about Boeing's grandfather rights that were letting the 737 get away with nearly half a dozen more seats than a comparable newly certified airliner could, all being equal.
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The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.
The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
Under operating instructions
'Electric stabilizer trim can be used to neutralise control column pitch forces before moving the stab trim switches to cutout'
Why wouldn't you?
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Maybe because the control loadings at the speed they were doing made it difficult/impossible to manually trim, so they tried the electric trim again? If you’ve got both (or even four) hands on the control column trying to stop the aircraft pitching down, there’s not many hands left for the manual trim...
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
Ok, I have to confess I’m confused.
All this talk of manual trim forces, etc.
MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.
If MCAS runs again, again any pilot trim action defeats MCAS.
There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.
Am I wrong?
- GY
All this talk of manual trim forces, etc.
MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.
If MCAS runs again, again any pilot trim action defeats MCAS.
There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.
Am I wrong?
- GY
Agreed.. I think the FAA's AD acknowledges the challenge that pilot's might face. At the bottom of (h) it reads:
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
actually it does.......
“Control airplane pitch attitude manually with control column and main electric trim as needed”
its the point in the memory items right after disengagjng the autopilot......
Agreed.. I think the FAA's AD acknowledges the challenge that pilot's might face. At the bottom of (h) it reads:
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
This should specify the possible symptoms.
It should then cover the AD items and go further to disconnecting ATS and flying pitch and thrust. It could well suggest reselecting flap and landing as soon as possible.
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Fairly poor handling of a serious investigation if you ask me.
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Agreed.. I think the FAA's AD acknowledges the challenge that pilot's might face. At the bottom of (h) it reads:
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
The pilots runaway stabilizer checklist.... is clear... operate the CUTOUT. It doesn't say... try and trim first. For me the AD has never been clear. Are the pilots supposed to follow their trained checklists... and the very same AD, a few paragraphs above, that simply says operate the CUTOUT... Or are they required to make the judgment that they'll never have the strength to turn the trim manually, so they need to rely on the failing electrical trim first.... and then CUTOUT?
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As these are terse instructions, if one might soon be grabbing a rotating wheel, and not long after that, hand cranking it, [would he] not want to do the best possible work with the electric trim before cutout?
Last edited by fotoguzzi; 4th Apr 2019 at 10:30. Reason: Complete sentence; cut down extra words
What is the direction of the pitching moment when extending the air brake in the 737 NG / Max, and separately (or as operationally used), when selecting flap from a clean configuration ?
How would slat extension affect these changes ?
Would the logical reverse be a reasonable assumption ?
GordonR, re PM,
and Ethiopian airliner down in Africa
How would slat extension affect these changes ?
Would the logical reverse be a reasonable assumption ?
GordonR, re PM,
and Ethiopian airliner down in Africa
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Clearly these incidents have raised many questions, especially for the trained professionals that operate the 737. The consequences of these accidents could maybe also demonstrate issues relating to trim on other 737 variants including the 737 NG. We must remain open to learning the lessons and exploring the wider implications.
If the Ethiopian crew did follow the Stabiliser Runaway memory actions as per QRH NNC, then clearly the very next action that would have followed would have been an attempt to use the manual trim handles. Should the excessive control loading have either blocked or restricted movement of that control due to control loading, the crew would find themselves in a perilous situation and dive. At that point out of desperation perhaps they tried to use the electric trim again and reactivated the electric trim cutout switches. I don't think that is too extraordinary to have attempted out of desperation if the trained procedures were failing were failing.
Manual control of trim on the 737 NG is usually straightforward, but it not impossible to find yourself possibly in a nasty situation. I have once experienced in a level D 738 sim following double engine flameout, high power nose high prior to failure, to a quick ensuing nose low dive. It shocked me the difficulty to raise the nose again and high loading on the manual trim handles. We recovered, but recall unloading the control column back pressure for a short time to help having read about such possible scenarios.
It is too early to say, but there could be lessons here not only just applicable to the Max but perhaps even the NG with regards to control loading whilst using manual trim. If we consider accidents including the 738 Fly Dubai nose dive, control loading implications to manual trim operation are important. After any stab trim runaway, it is essential that we have confidence in the effectiveness of the manual trim throughout the full range of movement and control loadings.
More attention is needed imo to why repeated AOA failures are happening on both 737 NG & Max variants.
For the crew operating these aircraft, there is little doubt that they were suddenly faced with multiple simultaneous failures and warnings. They had seconds to react to complex failures that could easily overload competent crews. If faced with Airspeed Unreliable, possibly altitude disagree, stick shaker, possible other master caution warnings, Stabiliser Runaway, increasing pitch down descent rate, followed by possible manual trim control being restricted by control loading (not proven yet) then they really did have a lot to deal with and the odds were stacked against them.
I think we should all be respectful to the families of the professionals that died trying in vain to regain control. It is too easy for armchair pilots to be judgmental without understanding the human factors and technical issues involved on the flight deck in these incidents. There is no evidence that crew training or that the airlines themselves had much if any involvement in outcome pf these accidents.
If the Ethiopian crew did follow the Stabiliser Runaway memory actions as per QRH NNC, then clearly the very next action that would have followed would have been an attempt to use the manual trim handles. Should the excessive control loading have either blocked or restricted movement of that control due to control loading, the crew would find themselves in a perilous situation and dive. At that point out of desperation perhaps they tried to use the electric trim again and reactivated the electric trim cutout switches. I don't think that is too extraordinary to have attempted out of desperation if the trained procedures were failing were failing.
Manual control of trim on the 737 NG is usually straightforward, but it not impossible to find yourself possibly in a nasty situation. I have once experienced in a level D 738 sim following double engine flameout, high power nose high prior to failure, to a quick ensuing nose low dive. It shocked me the difficulty to raise the nose again and high loading on the manual trim handles. We recovered, but recall unloading the control column back pressure for a short time to help having read about such possible scenarios.
It is too early to say, but there could be lessons here not only just applicable to the Max but perhaps even the NG with regards to control loading whilst using manual trim. If we consider accidents including the 738 Fly Dubai nose dive, control loading implications to manual trim operation are important. After any stab trim runaway, it is essential that we have confidence in the effectiveness of the manual trim throughout the full range of movement and control loadings.
More attention is needed imo to why repeated AOA failures are happening on both 737 NG & Max variants.
For the crew operating these aircraft, there is little doubt that they were suddenly faced with multiple simultaneous failures and warnings. They had seconds to react to complex failures that could easily overload competent crews. If faced with Airspeed Unreliable, possibly altitude disagree, stick shaker, possible other master caution warnings, Stabiliser Runaway, increasing pitch down descent rate, followed by possible manual trim control being restricted by control loading (not proven yet) then they really did have a lot to deal with and the odds were stacked against them.
I think we should all be respectful to the families of the professionals that died trying in vain to regain control. It is too easy for armchair pilots to be judgmental without understanding the human factors and technical issues involved on the flight deck in these incidents. There is no evidence that crew training or that the airlines themselves had much if any involvement in outcome pf these accidents.
So in sum, we have a non-DAL A system integrated with a secondary control system with no redundancy, monitoring, crew warnings or a dedicated means to disengage. Strap it to an aircraft where the trim system is more powerful than the primary controls and give it authority to move the stab at a far faster rate than normal trim and give it no limits of travel other than mechanical end-stops. If it goes wrong, force the crews to disable all powered stab control and equip them with manual trim wheels that are difficult and slow to operate at the best of times. Modify said wheels to make them slightly smaller and insert a more powerful damper to counteract the spring and backlash effect of the stab being moved at a faster rate than ever before - requiring an undocumented increase in physical effort. Finally inform the crews of this system's existence and get the company test pilots to retest all of this after a quick fatal crash, but do so only at a relatively slow speed. Second accident crew become the unexpected test pilots collecting a datapoint that suggests the trim wheel is impossible to move when at a higher airspeed. Cumulogranite awaits.
Apart from the flight envelop defining the configuration, CofG, AuW and airspeed/mach beyond which the manual wheels cannot be moved at an effective rate, what are we missing?
Apart from the flight envelop defining the configuration, CofG, AuW and airspeed/mach beyond which the manual wheels cannot be moved at an effective rate, what are we missing?
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[would he] not want to do the best possible work with the electric trim before cutout?
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https://www.documentcloud.org/docume...on-ET-302.html
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A few minutes ago the Ethiopian CAA website was still silent on this. There now only is minute information on the fact that there is an investigation and a ban.
In the case of recent Asian crashes the official websites were also hardly used or completely bypassed for either facebook and twitter reporting.
Lots of rules already, but another thing ICAO might take a look at. What is the minimum standard on reporting.
In many cases in any news situation the press gets an early view of things with an embargo till a certain time on publication. Might be the case here.
Another thing is the exceptional role the Ethiopian Airlines CEO has carved out for himself. He was one of the first on scene, shown handling evidence, reporting on the investigation, and continuing to do that. With all due respect, that is amazing, but in this case the only information available,...
In the case of recent Asian crashes the official websites were also hardly used or completely bypassed for either facebook and twitter reporting.
Lots of rules already, but another thing ICAO might take a look at. What is the minimum standard on reporting.
In many cases in any news situation the press gets an early view of things with an embargo till a certain time on publication. Might be the case here.
Another thing is the exceptional role the Ethiopian Airlines CEO has carved out for himself. He was one of the first on scene, shown handling evidence, reporting on the investigation, and continuing to do that. With all due respect, that is amazing, but in this case the only information available,...
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how would the ET302 pilots know
