AF 447 Thread No. 6
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Hi,
3holelover
I dunno about structural damage for THS .. but this ended with a big structural damage (the entire plane and it's load)
Maybe it's to understand Lyman prose as:
Why the THS still full up .. when the plane know (seem's the pilots no) he is in a full stall
Plane know this is a full stall .. plane know this is a full up THS deflection
The two are contradictory
Why not automatically reset the THS in a better position (with a warning to pilots) like it's a limitation for rudder deflection in particular situations ?
3holelover
Lyman.... Thanks for clarifying... One further comment, re: "If this airframe thinks enough of itself to protect the Rudder from inadvertent and harsh deflection, why would it not also want to protect itself from a TRIM trapped STALL?"
Because it is NOT "trapped" at all and there is no risk of structural damage as there is with the rudder.
Because it is NOT "trapped" at all and there is no risk of structural damage as there is with the rudder.
Maybe it's to understand Lyman prose as:
Why the THS still full up .. when the plane know (seem's the pilots no) he is in a full stall
Plane know this is a full stall .. plane know this is a full up THS deflection
The two are contradictory
Why not automatically reset the THS in a better position (with a warning to pilots) like it's a limitation for rudder deflection in particular situations ?
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So, once STALLED, there would not only seem to be no need for all NU from the THS, ....
With a continuous STALL warning, one would hope a 'smart' a/c would return the THS to neutral, and allow the Pilot to recover with elevators.
With a continuous STALL warning, one would hope a 'smart' a/c would return the THS to neutral, and allow the Pilot to recover with elevators.
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All of the AOA information to avoid this crash are present in every modern Airbus aircraft, as standard equipment. In addition to the stall warning and the VLS/Alpha Prot, Alpha max scale on the left side of the PFD, there is an even better, direct measure of AOA, even though it does not come from the AOA installed on the aircraft (3 on the 320 series).
The problem is, no one is trained to use it.
What is AOA? It is the angular difference between the relative wind and the longitudinal axis of the aircraft (chord of the wing, more specifically). In lay-mans terms (I am one), it is the difference between where the airplane is pointed, and where it is going, about the lateral axis.
Call up the "bird". With the wings level, the AOA is the vertical distance from the pitch bars (where the aircraft is pointed), and the "bird" (where the aircraft is actually going). Non-wings level, you visually drop a perpendicular from the plane of the pitch bars to the bird. That distance, measured on the PFD, is your AOA, and would have prevented this crash.
I know some engineer (I am one also) will say that this AOA measurement is not "perfect", but neither is an AOA gauge. Not even close. Just as IVSI is more useful than a pure VSI, this IRU based measurement is actually more user friendly to the pilot, more reliable, and "cleaner". And it is EXACTLY where the pilot is staring to control the aircraft, there is no other "scan" to learn.
On a 320 series, cruise is usually 2-3 degrees up, green dot, S, and F speed are 7-8, Stall warning (in alternate law in the sim) comes on at 10-12 degrees with the stall happening a bit above that. In level flight this is the "pitch attitude". In non-level flight, this is the perpendicular distance from the pitch bars to the bird. Icing doesn't affect the IRU's and there are 3 of them on the 320.
We were just not trained to use this.
The problem is, no one is trained to use it.
What is AOA? It is the angular difference between the relative wind and the longitudinal axis of the aircraft (chord of the wing, more specifically). In lay-mans terms (I am one), it is the difference between where the airplane is pointed, and where it is going, about the lateral axis.
Call up the "bird". With the wings level, the AOA is the vertical distance from the pitch bars (where the aircraft is pointed), and the "bird" (where the aircraft is actually going). Non-wings level, you visually drop a perpendicular from the plane of the pitch bars to the bird. That distance, measured on the PFD, is your AOA, and would have prevented this crash.
I know some engineer (I am one also) will say that this AOA measurement is not "perfect", but neither is an AOA gauge. Not even close. Just as IVSI is more useful than a pure VSI, this IRU based measurement is actually more user friendly to the pilot, more reliable, and "cleaner". And it is EXACTLY where the pilot is staring to control the aircraft, there is no other "scan" to learn.
On a 320 series, cruise is usually 2-3 degrees up, green dot, S, and F speed are 7-8, Stall warning (in alternate law in the sim) comes on at 10-12 degrees with the stall happening a bit above that. In level flight this is the "pitch attitude". In non-level flight, this is the perpendicular distance from the pitch bars to the bird. Icing doesn't affect the IRU's and there are 3 of them on the 320.
We were just not trained to use this.
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It seems to me....
...that many of you are looking for all sorts of things that either automation or aircraft systems of one sort or another could have done/be done in future to help in this situation, while forgetting that flying is an inherently dangerous undertaking that has, for eons now, been made rather routine by simply training pilots how to handle their machines.
Yes, you could automate the hell out of the thing, but at some point, somehow, all that automation could easily be counter productive.... Can't you imagine a situation, for instance, where a stab that returns to neutral automatically, might be a bad thing? Maybe it's best to leave the aircraft handling to pilots?
Maybe it's better to train pilots to fly, rather than manage computers?
This aircraft didn't fail. One system alone had what should have been a non earth shattering, temporary fault, due to ice crystals, but then it's pilot(s) failed.
Yes, as I said earlier, I agree there are probably some tweaks that might make sense, but I don't think anyone should get carried away in burying human failure with more complexity and more tacked-on, automated garbage that will wind up fouling somebody else down the road.
As yet, nobody wants to fly in a fully automated, pilotless aircraft. All we need, to get folks to their destination safely, in any serviceable aircraft, is a pilot who knows his machine, and knows how to fly it. That simple formula has been proven to be quite safe. What was missing here wasn't more junk, it was human knowledge and skill. Airmanship.
Does anyone here really believe an aircraft can be made that won't stall? My limited knowledge of aerodynamics and physics tells me, with current aircraft design, that's not possible. So pilots had better know how to recognize and correct for a stall. The surprise to me here, has been learning that hasn't been universally the case. That, imho, needs immediate correction!
...that many of you are looking for all sorts of things that either automation or aircraft systems of one sort or another could have done/be done in future to help in this situation, while forgetting that flying is an inherently dangerous undertaking that has, for eons now, been made rather routine by simply training pilots how to handle their machines.
Yes, you could automate the hell out of the thing, but at some point, somehow, all that automation could easily be counter productive.... Can't you imagine a situation, for instance, where a stab that returns to neutral automatically, might be a bad thing? Maybe it's best to leave the aircraft handling to pilots?
Maybe it's better to train pilots to fly, rather than manage computers?
This aircraft didn't fail. One system alone had what should have been a non earth shattering, temporary fault, due to ice crystals, but then it's pilot(s) failed.
Yes, as I said earlier, I agree there are probably some tweaks that might make sense, but I don't think anyone should get carried away in burying human failure with more complexity and more tacked-on, automated garbage that will wind up fouling somebody else down the road.
As yet, nobody wants to fly in a fully automated, pilotless aircraft. All we need, to get folks to their destination safely, in any serviceable aircraft, is a pilot who knows his machine, and knows how to fly it. That simple formula has been proven to be quite safe. What was missing here wasn't more junk, it was human knowledge and skill. Airmanship.
Does anyone here really believe an aircraft can be made that won't stall? My limited knowledge of aerodynamics and physics tells me, with current aircraft design, that's not possible. So pilots had better know how to recognize and correct for a stall. The surprise to me here, has been learning that hasn't been universally the case. That, imho, needs immediate correction!
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It seems to me....
...that many of you are looking for all sorts of things that either automation or aircraft systems of one sort or another could have done/be done in future to help in this situation, while forgetting that flying is an inherently dangerous undertaking that has, for eons now, been made rather routine by simply training pilots how to handle their machines.
...that many of you are looking for all sorts of things that either automation or aircraft systems of one sort or another could have done/be done in future to help in this situation, while forgetting that flying is an inherently dangerous undertaking that has, for eons now, been made rather routine by simply training pilots how to handle their machines.
Yes, you could automate the hell out of the thing, but at some point, somehow, all that automation could easily be counter productive.... Can't you imagine a situation, for instance, where a stab that returns to neutral automatically, might be a bad thing? Maybe it's best to leave the aircraft handling to pilots?
Maybe it's better to train pilots to fly, rather than manage computers?
Maybe it's better to train pilots to fly, rather than manage computers?
What is needed, is to eliminate or minimize the shortcomings in the design, which will reduce the risks of manual flying..
This aircraft didn't fail. One system alone had what should have been a non earth shattering, temporary fault, due to ice crystals, but then it's pilot(s) failed.
Yes, as I said earlier, I agree there are probably some tweaks that might make sense, but I don't think anyone should get carried away in burying human failure with more complexity and more tacked-on, automated garbage that will wind up fouling somebody else down the road.
As yet, nobody wants to fly in a fully automated, pilotless aircraft. All we need, to get folks to their destination safely, in any serviceable aircraft, is a pilot who knows his machine, and knows how to fly it. That simple formula has been proven to be quite safe. What was missing here wasn't more junk, it was human knowledge and skill. Airmanship.
Does anyone here really believe an aircraft can be made that won't stall? My limited knowledge of aerodynamics and physics tells me, with current aircraft design, that's not possible.
It would be nice to be able to make it so it would not stall. But I don't see that as an attainable goal.
However, it is achievable to improve the logic, the algorithms, the software subsystem, so that remarkable stability, and extraordinary structural integrity is not wasted if in a stall, by making the stall avoidance better, and stall recovery easier.
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3Hole
Don't you see a problem with an aircraft with an automatic trim system that trims silently? For years we have had alerting devices on THS trim movement (clackers & whoolers) to let you know the thing is moving. Then comes the new guy on the block with a "better" idea. (Airbus)
Couldn't they have seen the trim moving in their peripheral vision? Maybe, maybe not. There were serious problems in the cockpit that night that demanded attention.
If someone in the cockpit had noted that trim running up, they could have stopped it just like you would in a 707. Grab the trim wheel. Without all that nose up trim, the PF would have had serious trouble holding the nose up against the natural aerodynamic tendencies of the basic aircraft to drop its nose as it slowed. The PNF could have largely overridden the inept handling of the PF if it had occurred to him.
But no one saw the trim move. No one heard it move. If they had thought about it, they should have anticipated it moving, but they had other problems and it bit them.
We have now lost two Airbus aircraft due to lack of crew awareness of trim position and (other problems). Fixing the trim system to provide better motion alerting should be easy. It has plenty of precedents and it is not rocket sciences.
Don't you see a problem with an aircraft with an automatic trim system that trims silently? For years we have had alerting devices on THS trim movement (clackers & whoolers) to let you know the thing is moving. Then comes the new guy on the block with a "better" idea. (Airbus)
Couldn't they have seen the trim moving in their peripheral vision? Maybe, maybe not. There were serious problems in the cockpit that night that demanded attention.
If someone in the cockpit had noted that trim running up, they could have stopped it just like you would in a 707. Grab the trim wheel. Without all that nose up trim, the PF would have had serious trouble holding the nose up against the natural aerodynamic tendencies of the basic aircraft to drop its nose as it slowed. The PNF could have largely overridden the inept handling of the PF if it had occurred to him.
But no one saw the trim move. No one heard it move. If they had thought about it, they should have anticipated it moving, but they had other problems and it bit them.
We have now lost two Airbus aircraft due to lack of crew awareness of trim position and (other problems). Fixing the trim system to provide better motion alerting should be easy. It has plenty of precedents and it is not rocket sciences.
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Machinbird,
It is clear that the silent trim was not helpful in that stressful situation, and you've eloquently explained that.
But I am going further.
The trim should have stopped, or should have never happen during the Stall.
The a/c computers determined that the a/c was in a Stall, and sounded the alarm for 53 seconds.
During those very 53 seconds, the autotrim moved silently the THS to its extreme position of -13 degrees of max NU.
It is clear that there was a logical disconnect between the Stall and Autotrim. Had there been a logical connection, with a locking of the THS in Neutral, it would have certainly helped the pilots, the recovery from Stall.
During the rest of the descent, the Stall Warning sounded another 8 times, and the THS has remained in its max NU during all those 8 Stall Warnings.
Should the THS have returned to Neutral at the first Stall Warning out of those 8, the recovery would have been helped.
It is clear that the silent trim was not helpful in that stressful situation, and you've eloquently explained that.
But I am going further.
The trim should have stopped, or should have never happen during the Stall.
The a/c computers determined that the a/c was in a Stall, and sounded the alarm for 53 seconds.
During those very 53 seconds, the autotrim moved silently the THS to its extreme position of -13 degrees of max NU.
It is clear that there was a logical disconnect between the Stall and Autotrim. Had there been a logical connection, with a locking of the THS in Neutral, it would have certainly helped the pilots, the recovery from Stall.
During the rest of the descent, the Stall Warning sounded another 8 times, and the THS has remained in its max NU during all those 8 Stall Warnings.
Should the THS have returned to Neutral at the first Stall Warning out of those 8, the recovery would have been helped.
3Hole
Don't you see a problem with an aircraft with an automatic trim system that trims silently? For years we have had alerting devices on THS trim movement (clackers & whoolers) to let you know the thing is moving. Then comes the new guy on the block with a "better" idea. (Airbus)
Couldn't they have seen the trim moving in their peripheral vision? Maybe, maybe not. There were serious problems in the cockpit that night that demanded attention.
If someone in the cockpit had noted that trim running up, they could have stopped it just like you would in a 707. Grab the trim wheel. Without all that nose up trim, the PF would have had serious trouble holding the nose up against the natural aerodynamic tendencies of the basic aircraft to drop its nose as it slowed. The PNF could have largely overridden the inept handling of the PF if it had occurred to him.
But no one saw the trim move. No one heard it move. If they had thought about it, they should have anticipated it moving, but they had other problems and it bit them.
We have now lost two Airbus aircraft due to lack of crew awareness of trim position and (other problems). Fixing the trim system to provide better motion alerting should be easy. It has plenty of precedents and it is not rocket sciences.
Don't you see a problem with an aircraft with an automatic trim system that trims silently? For years we have had alerting devices on THS trim movement (clackers & whoolers) to let you know the thing is moving. Then comes the new guy on the block with a "better" idea. (Airbus)
Couldn't they have seen the trim moving in their peripheral vision? Maybe, maybe not. There were serious problems in the cockpit that night that demanded attention.
If someone in the cockpit had noted that trim running up, they could have stopped it just like you would in a 707. Grab the trim wheel. Without all that nose up trim, the PF would have had serious trouble holding the nose up against the natural aerodynamic tendencies of the basic aircraft to drop its nose as it slowed. The PNF could have largely overridden the inept handling of the PF if it had occurred to him.
But no one saw the trim move. No one heard it move. If they had thought about it, they should have anticipated it moving, but they had other problems and it bit them.
We have now lost two Airbus aircraft due to lack of crew awareness of trim position and (other problems). Fixing the trim system to provide better motion alerting should be easy. It has plenty of precedents and it is not rocket sciences.
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Hi,
I will repeat this X1000 if needed:
The Pitot tube was not faulty
As many here like write about the plane ...
The pitot tube operated normally .. as required by its specifications and certifications
The problem is that the measuring instrument has been used outside his operating range
Ice crystals is not a area for use Pitot tube .. it's not in the certifications
As the plane went well until he was out of its flight envelop
As the pilots went well .. until they were (or put their self) in a situation out of their skill
This aircraft didn't fail. One system alone had what should have been a non earth shattering, temporary fault, due to ice crystals, but then it's pilot(s) failed.
The Pitot tube was not faulty
As many here like write about the plane ...
The pitot tube operated normally .. as required by its specifications and certifications
The problem is that the measuring instrument has been used outside his operating range
Ice crystals is not a area for use Pitot tube .. it's not in the certifications
As the plane went well until he was out of its flight envelop
As the pilots went well .. until they were (or put their self) in a situation out of their skill
Last edited by jcjeant; 18th Aug 2011 at 05:51.
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Hi,
Pending a resolution of Airbus engineers and certification in 10 years .. pilots can easily solve the problem of silent motion trim
No rocket sciences indeed ...
Fixing the trim system to provide better motion alerting should be easy. It has plenty of precedents and it is not rocket sciences.
Pending a resolution of Airbus engineers and certification in 10 years .. pilots can easily solve the problem of silent motion trim
No rocket sciences indeed ...
It is clear that there was a logical disconnect between the Stall and Autotrim. Had there been a logical connection, with a locking of the THS in Neutral, it would have certainly helped the pilots, the recovery from Stall.
- Making the trim operation audible (this seems like a no brainer). Relying on the visual cues seems over optimistic, particularly when things have already gone pear-shaped.
- Auto-neutralizing trim state in stall warning. Unless I am misunderstanding things here, the trim was not what stood this aircraft on it's tail, it was the PF elevator input. My understanding is that the elevators alone can override the THS. Would neutralizing the THS have been the key here to save the aircraft? I don't think so at all. The PF (and PNF+Captain) at no point acknowledged the STALL. In fact the PF was demanding NU pitch for most of the time - he got what he asked for. Would the PF have NOT demanded NU if the THS has not followed his demands... or had untrimmed? Doubtful.
I do believe a better more explicit YOU ARE STALLED alerting system can be implemented. The aircraft knows enough from AoA, Vertical Speed and perhaps Ground Speed to be able to state quite happily "You are stalled and plummeting to certain doom - how about reducing AoA with a bit of nose down old chap...". OK may be that's a bit glib, but something beyond the existing Stall Warning audible ---> "AIRCRAFT STALLED! AIRCRAFT STALLED! REDUCE AoA!"
jcjeant
I believe that you are too quick to defend the pitot tube as not being at fault. The earlier poster had specifically stated "pitot system"
It was the speed measuring system at fault (the pitot was only a part of it). Of course you are correct that such a system fault was presumed at aircraft certification..
At this point the assumption is that a combination of systems or unlikely events probably caused the accident. The issue now is what needs to be fixed to prevent another accident.
It is not enough to change the pitot tube alone when clearly a system fault was not accomodated to continued safe flight and landing.
I will repeat this X1000 if needed:
The Pitot tube was not faulty
As many here like write about the plane ...
The pitot tube operated normally .. as required by its specifications and certifications
The problem is that the measuring instrument has been used outside his operating range
Ice crystals is not a area for use Pitot tube .. it's not in the certifications
As the plane went well until he was out of its flight envelop
As the pilots went well .. until they were (or put their self) in a situation out of their skill
The Pitot tube was not faulty
As many here like write about the plane ...
The pitot tube operated normally .. as required by its specifications and certifications
The problem is that the measuring instrument has been used outside his operating range
Ice crystals is not a area for use Pitot tube .. it's not in the certifications
As the plane went well until he was out of its flight envelop
As the pilots went well .. until they were (or put their self) in a situation out of their skill
I believe that you are too quick to defend the pitot tube as not being at fault. The earlier poster had specifically stated "pitot system"
It was the speed measuring system at fault (the pitot was only a part of it). Of course you are correct that such a system fault was presumed at aircraft certification..
At this point the assumption is that a combination of systems or unlikely events probably caused the accident. The issue now is what needs to be fixed to prevent another accident.
It is not enough to change the pitot tube alone when clearly a system fault was not accomodated to continued safe flight and landing.
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Hi Garage Years,
I agree. It is pointless adding more audible warnings to already saturated pilots.
Altitude Alert, Multiple Ecam Dings, Autopilot Disconnect, Thrust Lock Dings etc. + "Stall Stall".
A different warning / alert is required to elevate it to the highest attention getter - like the discrete stall warning vibrations through the control column on other aircraft. It simulates the natural buffet onset. There is no other warning like it.
The audible "Stall Stall" seems to have been filtered out of all 3 crew members sensory perception - no one commented on it.
I agree. It is pointless adding more audible warnings to already saturated pilots.
Altitude Alert, Multiple Ecam Dings, Autopilot Disconnect, Thrust Lock Dings etc. + "Stall Stall".
A different warning / alert is required to elevate it to the highest attention getter - like the discrete stall warning vibrations through the control column on other aircraft. It simulates the natural buffet onset. There is no other warning like it.
The audible "Stall Stall" seems to have been filtered out of all 3 crew members sensory perception - no one commented on it.
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....
- Auto-neutralizing trim state in stall warning. Unless I am misunderstanding things here, the trim was not what stood this aircraft on it's tail, it was the PF elevator input. My understanding is that the elevators alone can override the THS. Would neutralizing the THS have been the key here to save the aircraft? I don't think so at all.
- Auto-neutralizing trim state in stall warning. Unless I am misunderstanding things here, the trim was not what stood this aircraft on it's tail, it was the PF elevator input. My understanding is that the elevators alone can override the THS. Would neutralizing the THS have been the key here to save the aircraft? I don't think so at all.
The "THS Neutral + Elevators ND" would have allowed an immediate more effective Elevators ND, compared with the "THS max NU + Elevators ND".
I do believe a better more explicit YOU ARE STALLED alerting system can be implemented. ...
Last edited by airtren; 18th Aug 2011 at 13:36.
Retired F4
As caveated by our contributor, the scenario might not have been similar enough to have triggered a "this is one of those situations" responses from the crew.
What I was trying to get at (damping and pitch rate limiting functions considered) is that I think the pitch rates would be a little faster (you'd have to wait less time) if you moved the THS with the wheels (even when auto trim is functioning, which it should in Alt 2) rather than wait for the elevator THS linkage to induce THS nose down (THS actually up a bit) commands.
But if one doesn't train it, one probably doesn't resort to such actionns when things get hairy in the cockpit.
As caveated by our contributor, the scenario might not have been similar enough to have triggered a "this is one of those situations" responses from the crew.
What I was trying to get at (damping and pitch rate limiting functions considered) is that I think the pitch rates would be a little faster (you'd have to wait less time) if you moved the THS with the wheels (even when auto trim is functioning, which it should in Alt 2) rather than wait for the elevator THS linkage to induce THS nose down (THS actually up a bit) commands.
But if one doesn't train it, one probably doesn't resort to such actionns when things get hairy in the cockpit.
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How hard would it be to just post a little animated graphic of the fin/stab configuration? Something that can be instantly visually absorbed? "Wow that can't be right.."
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Hi,
lomapaseao
The Pitot tube is not only a part of it .. it's the most important part of it
Remove from the plane the Pitot tube and you have no more speed measuring system at all
The AF447 case proven this.
The best solution at today date is to use the Pitot tube in his domain of certification
So .. dont fly in ice crystal area ..
If not able to detect ice crystal .. don't fly in the areas when this is the possibility to meet them .. forget fuel sparing .. fly safe !
lomapaseao
I believe that you are too quick to defend the pitot tube as not being at fault. The earlier poster had specifically stated "pitot system"
It was the speed measuring system at fault (the pitot was only a part of it). Of course you are correct that such a system fault was presumed at aircraft certification..
It was the speed measuring system at fault (the pitot was only a part of it). Of course you are correct that such a system fault was presumed at aircraft certification..
Remove from the plane the Pitot tube and you have no more speed measuring system at all
The AF447 case proven this.
The best solution at today date is to use the Pitot tube in his domain of certification
So .. dont fly in ice crystal area ..
If not able to detect ice crystal .. don't fly in the areas when this is the possibility to meet them .. forget fuel sparing .. fly safe !
Lonewolf_50
Lonewolf_50
Retired F4
As caveated by our contributor, the scenario might not have been similar enough to have triggered a "this is one of those situations" responses from the crew.
What I was trying to get at (damping and pitch rate limiting functions considered) is that I think the pitch rates would be a little faster (you'd have to wait less time) if you moved the THS with the wheels (even when auto trim is functioning, which it should in Alt 2) rather than wait for the elevator THS linkage to induce THS nose down (THS actually up a bit) commands.
But if one doesn't train it, one probably doesn't resort to such actionns when things get hairy in the cockpit.
Retired F4
As caveated by our contributor, the scenario might not have been similar enough to have triggered a "this is one of those situations" responses from the crew.
What I was trying to get at (damping and pitch rate limiting functions considered) is that I think the pitch rates would be a little faster (you'd have to wait less time) if you moved the THS with the wheels (even when auto trim is functioning, which it should in Alt 2) rather than wait for the elevator THS linkage to induce THS nose down (THS actually up a bit) commands.
But if one doesn't train it, one probably doesn't resort to such actionns when things get hairy in the cockpit.
Iīm fully with you at that, but:
I wanted to make it clear, that i couldnīt find a reference in the valid publications for aircrew (FCOM, FTCOM) and maintenance (LTTM), which even would give a hint to use manual trim in such cases.
So how should the crew know about it?
Why should it have been trained?
Did anybody knew it before AF447?
On what basis would it be trained now?
We had the manual trim discussion before on the older thread, but there everybody asssumed direct law, where only manual trim is available.
We even dont know, how the system will behave after manual trim has been applied despite autotrim still active.
(Ref. LTTM)
Operation/Control and Indicating
When you turn the handwheel installed in the cockpit center pedestal the chain and cable loop move the input shaft. The input shaft moves the mechanical servoloop mechanism through an override mechanism. The override mechanism, which is installed adjacent to the Pitch Trim Actuator (PTA), makes sure that the mechanical control cancels the electrical control.
When you turn the handwheel installed in the cockpit center pedestal the chain and cable loop move the input shaft. The input shaft moves the mechanical servoloop mechanism through an override mechanism. The override mechanism, which is installed adjacent to the Pitch Trim Actuator (PTA), makes sure that the mechanical control cancels the electrical control.
Operation of the Override Mechanism
Operation of the Mechanical Control
The input shaft turns.
A cam in the shape of a V turns.
The cam moves a roller which disconnects the internal microteeth from the
output shaft of the PTA.
At the same time a piston is pushed to operate the three override mechanism microswitches.
The mechanical control now comes on before the electrical control.
Release of the Mechanical Control
The input shaft stops.
The cam in the PTA is released.
The internal springs connect the internal microteeth to the output shaft of
the PTA.
At the same time the piston moves back from the microswitches.
The mechanism is now set in the electrical control position.
Operation of the Mechanical Control
The input shaft turns.
A cam in the shape of a V turns.
The cam moves a roller which disconnects the internal microteeth from the
output shaft of the PTA.
At the same time a piston is pushed to operate the three override mechanism microswitches.
The mechanical control now comes on before the electrical control.
Release of the Mechanical Control
The input shaft stops.
The cam in the PTA is released.
The internal springs connect the internal microteeth to the output shaft of
the PTA.
At the same time the piston moves back from the microswitches.
The mechanism is now set in the electrical control position.
MECHANICAL INPUT SHAFT
The Mechanical input shaft connects the mechanical control loop and theTHS
actuator. The shaft has a flange which is connected to the mechanical input of the THS actuator. The other end of the shaft has a sprocket. The mechanical control-loop chain is installed on the sprocket
The Mechanical input shaft connects the mechanical control loop and theTHS
actuator. The shaft has a flange which is connected to the mechanical input of the THS actuator. The other end of the shaft has a sprocket. The mechanical control-loop chain is installed on the sprocket
Point is: We know now, that trimming the THS manually would have helped to bring the nose down. But we dont know consequences in other circumstances, as there seems to be no documentation concerning such a usage. So how can one train for it without documentation?