Pitch trim - poorly understood?
Join Date: Aug 2005
Location: London
Posts: 78
Likes: 0
Received 0 Likes
on
0 Posts
FGD
The incident I quoted was (probably) a little different to the FlyDubai in that what I saw was a simulated Cat 3a GA from the flare following an Autopilot failure. In that case the speed was very low, so trim is more nose-up + there was the nose up bias that's fed in at low level (nominally at 400ft Radio), and the control deflection to counteract the nose up pitch from the engines is large. As I understand it, the the flyDubai went around from a higher altitude , possibly above the height at which the auto pitch trim is applied, and logically at a much higher speed than in the flare, both of which should have minimised the difficulty of trimming for the go-around. There are also reports that the airline did all approaches manually using a HUD, in which case I would assume no auto pitch trim would have been applied. Finally, the incident I quoted happened very quickly, very close to the ground, whileFlyDubai seems to have climbed a few thousand feet before losing it. All in all quite a different scenario. I wouldn't exclude the possibility of confusion over the functioning of the pitch control system as I described in the Roger-Wilco article, because as I've said, so few people seem to understand it, and that understanding matters most when large pitch changes occur (as in any GA). But if it did play a part, I suspect there were other errors too. We'll just have to wait for the report.
Thanks for the interest from you and framer
The incident I quoted was (probably) a little different to the FlyDubai in that what I saw was a simulated Cat 3a GA from the flare following an Autopilot failure. In that case the speed was very low, so trim is more nose-up + there was the nose up bias that's fed in at low level (nominally at 400ft Radio), and the control deflection to counteract the nose up pitch from the engines is large. As I understand it, the the flyDubai went around from a higher altitude , possibly above the height at which the auto pitch trim is applied, and logically at a much higher speed than in the flare, both of which should have minimised the difficulty of trimming for the go-around. There are also reports that the airline did all approaches manually using a HUD, in which case I would assume no auto pitch trim would have been applied. Finally, the incident I quoted happened very quickly, very close to the ground, whileFlyDubai seems to have climbed a few thousand feet before losing it. All in all quite a different scenario. I wouldn't exclude the possibility of confusion over the functioning of the pitch control system as I described in the Roger-Wilco article, because as I've said, so few people seem to understand it, and that understanding matters most when large pitch changes occur (as in any GA). But if it did play a part, I suspect there were other errors too. We'll just have to wait for the report.
Thanks for the interest from you and framer
Join Date: Apr 2008
Location: nowhere
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
It seems to me that a big part of the problem is the large amount of thrust which is why the aircraft is pitching up so much to begin with. Some of the bigger Boeings which are typically on automatics are designed to only add enough thrust for a 2000 fpm climb if the TOGA switch is pushed once. I am not sure about the 737-800.
I remember in the old 727 being empty on a cold day with a 6000 fpm climb with a level off coming up. All was solved by bringing the power back about halfway at least 1500 feet before level off resulting in a nice reduction toward a 1000 fpm climb and level off for the last 1000 feet of climb.
That being said, the flaps had been retracted at this point. But on a manually flown go-around with a high climb rate and a fairly low altitude level off, there can be some conflicting limits. The missed approach altitude is nearing quickly with a high climb rate resulting in a desire to push forward on the controls to avoid passing through it, but there is also a speed limit on the flap setting. Things start happening very fast which can perhaps easily be slowed down significantly by disconnecting the autothrottle and reducing thrust. Perhaps some button pushing can be done with the autothrottle connected but there seems to be a time lag doing this.
I remember in the old 727 being empty on a cold day with a 6000 fpm climb with a level off coming up. All was solved by bringing the power back about halfway at least 1500 feet before level off resulting in a nice reduction toward a 1000 fpm climb and level off for the last 1000 feet of climb.
That being said, the flaps had been retracted at this point. But on a manually flown go-around with a high climb rate and a fairly low altitude level off, there can be some conflicting limits. The missed approach altitude is nearing quickly with a high climb rate resulting in a desire to push forward on the controls to avoid passing through it, but there is also a speed limit on the flap setting. Things start happening very fast which can perhaps easily be slowed down significantly by disconnecting the autothrottle and reducing thrust. Perhaps some button pushing can be done with the autothrottle connected but there seems to be a time lag doing this.
But if you are not up to scratch with a manual GA on instruments in IMC, especially if you are slow to operate the stab trim in conjunction with forward elevator to ease the stick forces as the pitch up occurs, then the pitch angle can quickly increase to a dangerous angle.
"If normal pitch control inputs do not stop an increasing pitch rate, rolling the airplane to a bank angle that starts the nose down should work. Bank angles of about 45 degrees, up to a maximum of 60 degrees could be needed. Unloading the wing by maintaining continuous nose-down elevator pressure keeps the wing angle of attack as low as possible making the normal controls as effective as possible.
With airspeed as low as stick shaker onset, normal roll controls - up to full deflection of ailerons and spoilers - may be used. The rolling maneuver changes the pitch rate into a turning maneuver, allowing the pitch to decrease. Finally, if normal pitch control then roll control is ineffective, careful rudder input in the direction of the desired roll may be required to induce a rolling maneuver. for recovery.
Only a small amount of rudder is needed. Too much rudder applied too quickly or held too long may result in loss of lateral and directional control. Because of the low energy condition, pilots should exercise caution when applying rudder. The reduced pitch attitude allows airspeed to increase, thereby improving elevator and aileron effectiveness. After the pitch attitude and airspeed return to the desired range the pilot can reduce angle of bank with normal lateral flight controls and return the airplane to normal flight". Unquote
............................................................ ...............................................
That advice is gold standard and should be learned by heart for all pilots as it applies in general to most types of aircraft from Cessna 150 to Boeing 737.
Because of the relative complexity of this recovery action from high pitch angles, it is should be practiced regularly in the simulator under simulated IMC. That is because when unusual attitude situations occur such as those described above, it is most likely at night or in IMC.
From the above, and that includes the Boeing FCTM advice, it is easy to understand the vital importance for pilots to maintain their basic instrument flying skills on raw data.
I have flown several types that have pitch trimming effected by a variable incidence tailplane/horizontal stabiliser but have never come across one that has the problems alluded to for the B737. This has set me thinking ....
I think that the first issue is predictably following an AP disconnect. If an aircraft is in trim, the pilot will control the aircraft in pitch intuitively. However, if it is sometimes in trim, sometimes not and by differing amounts then it will be very unpredictable and there will be a finite reaction time before the pilot starts to make any required inputs. I have flown one aircraft that was longitudinally statically stable and did not have any follow-up trim post engagement. Therefore, if a disconnect occurred and there had been a speed change since engagement then the aircraft would be out of trim. However, it was still predictable because knowledge of the speed variation from selection fitted a mental model of the aircraft's flying qualities and it was consistent.
The second consideration relating to out of trim conditions is whether the pilot is attempting to maintain a constant pitch attitude or to generate a pitch rate. If he/she is attempting to maintain an attitude and has the elevator authority to do so (i.e, requires less than full elevator), the force can be held initially and then stabiliser trim inputs made. The force will reduce and the control column will need to be moved back towards the trim position. However, whilst retrimming the pilot will subconsciously be correcting any errors in the desired pitch attitude via yoke displacements rather than forces and so the aircraft's response will still be predictable.
I believe that the problem aspect is when the pilot is trying to generate a pitch rate but full elevator deflection does not give him the required rate. In the case of a low manual go-around with an AP disconnect following an AP nose up trim input and a nose up pitching moment due to power, a nose up pitch rate may exist even if the pilot applies full forward yoke. If nose down stab trim is applied simultaneously, a nose down pitch rate should eventually be generated, and due to the resulting steep nose up attitude a nose down pitch rate is now required to regain the desired pitch attitude. This pitch rate will be generated by both the elevator and the stabiliser but the pilot has no sense of the relative contributions of the two controls. When the desired pitch attitude is achieved, aft movement of the yoke may not stop the nose down pitch rate if too much stabiliser trim has been applied and even with full aft yoke the nose may continue to pitch nose down. I suspect that this is why the Boeing FCTM advice posted by Centaurus advocates the use of bank and not simultaneous elevator inputs and stabiliser trim; the key is in the first line when it refers to "pitch rate".
I think that the first issue is predictably following an AP disconnect. If an aircraft is in trim, the pilot will control the aircraft in pitch intuitively. However, if it is sometimes in trim, sometimes not and by differing amounts then it will be very unpredictable and there will be a finite reaction time before the pilot starts to make any required inputs. I have flown one aircraft that was longitudinally statically stable and did not have any follow-up trim post engagement. Therefore, if a disconnect occurred and there had been a speed change since engagement then the aircraft would be out of trim. However, it was still predictable because knowledge of the speed variation from selection fitted a mental model of the aircraft's flying qualities and it was consistent.
The second consideration relating to out of trim conditions is whether the pilot is attempting to maintain a constant pitch attitude or to generate a pitch rate. If he/she is attempting to maintain an attitude and has the elevator authority to do so (i.e, requires less than full elevator), the force can be held initially and then stabiliser trim inputs made. The force will reduce and the control column will need to be moved back towards the trim position. However, whilst retrimming the pilot will subconsciously be correcting any errors in the desired pitch attitude via yoke displacements rather than forces and so the aircraft's response will still be predictable.
I believe that the problem aspect is when the pilot is trying to generate a pitch rate but full elevator deflection does not give him the required rate. In the case of a low manual go-around with an AP disconnect following an AP nose up trim input and a nose up pitching moment due to power, a nose up pitch rate may exist even if the pilot applies full forward yoke. If nose down stab trim is applied simultaneously, a nose down pitch rate should eventually be generated, and due to the resulting steep nose up attitude a nose down pitch rate is now required to regain the desired pitch attitude. This pitch rate will be generated by both the elevator and the stabiliser but the pilot has no sense of the relative contributions of the two controls. When the desired pitch attitude is achieved, aft movement of the yoke may not stop the nose down pitch rate if too much stabiliser trim has been applied and even with full aft yoke the nose may continue to pitch nose down. I suspect that this is why the Boeing FCTM advice posted by Centaurus advocates the use of bank and not simultaneous elevator inputs and stabiliser trim; the key is in the first line when it refers to "pitch rate".
Moderator
One of the sideline issues is training and exposure to such problems .. unfortunately not always addressed adequately in these modern fiscally driven days.
I recall (quite fondly) my first tailwheel endorsement on the SuperCub. A very thorough endorsement, it included a full flap, min approach speed, in trim final approach and then the miss.
The stick load was like nothing I had experienced to that time in my flying career (probably around 100 hours or so total).
One of those experiences which progressively convinced me of the need for pilot exposure to out of the routine flight events in the simulator in later years. The time not to get a surprise first time around is in the heat of the real moment ..
I recall (quite fondly) my first tailwheel endorsement on the SuperCub. A very thorough endorsement, it included a full flap, min approach speed, in trim final approach and then the miss.
The stick load was like nothing I had experienced to that time in my flying career (probably around 100 hours or so total).
One of those experiences which progressively convinced me of the need for pilot exposure to out of the routine flight events in the simulator in later years. The time not to get a surprise first time around is in the heat of the real moment ..
Join Date: Jan 2008
Location: farmm intersection, our ranch
Age: 57
Posts: 206
Likes: 0
Received 0 Likes
on
0 Posts
This pitch rate will be generated by both the elevator and the stabiliser but the pilot has no sense of the relative contributions of the two controls. When the desired pitch attitude is achieved, aft movement of the yoke may not stop the nose down pitch rate if too much stabiliser trim has been applied and even with full aft yoke the nose may continue to pitch nose down.
15 seconds of trim, flaps up, will change the in trim speed by 100 knots (737-800). It would be more speed / less time with flaps out.
I wonder what the perception would be if the other pilot were applying some opposite force to the yoke.
flyingchanges,
In this situation force only becomes an issue if it is so high that full elevator deflection cannot be achieved, which could occur with manual, unpowered controls. The problem here is one of elevator authority, which is a function of displacement rather than force.
In this situation force only becomes an issue if it is so high that full elevator deflection cannot be achieved, which could occur with manual, unpowered controls. The problem here is one of elevator authority, which is a function of displacement rather than force.
Join Date: Jun 2006
Location: Left Coast USA
Posts: 75
Likes: 0
Received 0 Likes
on
0 Posts
Centaurus, Boeing definitely recommends unloading the wings in nose high attitude upset, great technique, however, probably not in a low altitude GA in the soup.
Capn Bloggs offers the most relevant lesson, IMHO,
1. Pitch to attitude.
2. Trim out stick forces.
Safer Journies,
Sushi
Capn Bloggs offers the most relevant lesson, IMHO,
1. Pitch to attitude.
2. Trim out stick forces.
Safer Journies,
Sushi
Join Date: Oct 2008
Location: UK
Posts: 361
Likes: 0
Received 0 Likes
on
0 Posts
Gentlemen, thank you for not only an informed discussion, but one refreshingly free of hysteria and childish one upmanship.
I don't want to drive the discussion too far away from its intended purpose, but turning briefly for a moment to the specifics of the FZ accident, I would like to clarify some points.
FZ do not authorise their crew to fly dual AP approaches, so in this instance, talk of nose up trim at the point of GA would not apply. The latter stages of the approach (typically from around 1000' AGL), are hand flown, and it's reasonable to expect that this means an in trim aircraft at the point of GA. Autopilot and autothrottle are typically disengaged together.
The FZ airframe involved was fitted with 27K rated engines. My understanding is that standard GA thrust, from a single push on the TOGA button, gives 26K thrust. This is more than adequate to achieve a relatively unexciting rate of climb (between 1000-2000fpm) as previously mentioned. As the aircraft was relatively light, I would expect closer to the higher rate.
In relation to the approach prior to the accident, it is not clear exactly what the configuration of the aircraft was (flap 15 or 30), or whether the AP was still engaged or not. These could have a significant bearing on the response to the GA. We also don't know the reason for the GA, except that it took place somewhere around 1400-1500' AGL. The weather conditions were a strong, quartering headwind, with a significant increase in the lower levels above the point of GA - from some 25kts on the field to 60kts at the final altitude reached.
Purely for the purposes of discussion, I would be very interested to know the likely effect on the aircraft trim system in the following circumstances:
Autopilot engaged, final landing configuration of gear down, flap 30. At approx 1500', a hard windshear warning ("windshear, windshear, windshear" from the EGPWS). As the autopilot and autothrottle are both still engaged, the PF pushes TOGA and activates an automatic, AP coupled windshear escape manoeuvre. This will be with the full 27K thrust available.
Assuming no change of configuration, and a rapidly increasing headwind, what is the trim system going to do? How long would the STS run before potentially reaching the limit of its full authority?
If (and I mean IF), the crew misidentify an excessively long STS trim, coupled with unusually high pitch, as a trim runaway, what is the immediate aircraft response going to be on AP disconnect? How much more difficult does the situation become if the Stab Trim cutout switches are activated?
I'm embarrassed to admit, it's way beyond my current understanding. I have an idea, but that is the whole point if this thread. People have ideas, but usually grounded in an incomplete or inadequate knowledge of the system.
I don't want to drive the discussion too far away from its intended purpose, but turning briefly for a moment to the specifics of the FZ accident, I would like to clarify some points.
FZ do not authorise their crew to fly dual AP approaches, so in this instance, talk of nose up trim at the point of GA would not apply. The latter stages of the approach (typically from around 1000' AGL), are hand flown, and it's reasonable to expect that this means an in trim aircraft at the point of GA. Autopilot and autothrottle are typically disengaged together.
The FZ airframe involved was fitted with 27K rated engines. My understanding is that standard GA thrust, from a single push on the TOGA button, gives 26K thrust. This is more than adequate to achieve a relatively unexciting rate of climb (between 1000-2000fpm) as previously mentioned. As the aircraft was relatively light, I would expect closer to the higher rate.
In relation to the approach prior to the accident, it is not clear exactly what the configuration of the aircraft was (flap 15 or 30), or whether the AP was still engaged or not. These could have a significant bearing on the response to the GA. We also don't know the reason for the GA, except that it took place somewhere around 1400-1500' AGL. The weather conditions were a strong, quartering headwind, with a significant increase in the lower levels above the point of GA - from some 25kts on the field to 60kts at the final altitude reached.
Purely for the purposes of discussion, I would be very interested to know the likely effect on the aircraft trim system in the following circumstances:
Autopilot engaged, final landing configuration of gear down, flap 30. At approx 1500', a hard windshear warning ("windshear, windshear, windshear" from the EGPWS). As the autopilot and autothrottle are both still engaged, the PF pushes TOGA and activates an automatic, AP coupled windshear escape manoeuvre. This will be with the full 27K thrust available.
Assuming no change of configuration, and a rapidly increasing headwind, what is the trim system going to do? How long would the STS run before potentially reaching the limit of its full authority?
If (and I mean IF), the crew misidentify an excessively long STS trim, coupled with unusually high pitch, as a trim runaway, what is the immediate aircraft response going to be on AP disconnect? How much more difficult does the situation become if the Stab Trim cutout switches are activated?
I'm embarrassed to admit, it's way beyond my current understanding. I have an idea, but that is the whole point if this thread. People have ideas, but usually grounded in an incomplete or inadequate knowledge of the system.
Boeing definitely recommends unloading the wings in nose high attitude upset, great technique, however, probably not in a low altitude GA in the soup.
1. Watch the aircraft stall since his current control movements have failed to stop the speed bleed and in a few seconds he and his passengers are dead.
2. Take only some of the Boeing FCTM advice and roll the aircraft to drop the nose to permit speed gain; disregard the advice to unload to better aid recovery and instead pull back on the stick to prevent height loss near the ground.
3 Take the full Boeing FCTM advice which includes unloading the wings during the roll manoeuvre regardless of proximity of nearby terrain and hope you have acted soon enough.
Your choice. I sure know which option I would choose.
The mechanics of trimming a stabiliser/elevator combo are very interesting and one hopes that all who fly such things have a working understanding, especially on aircraft that have a pronounced pitch-power couple.
One thing that strikes me is that if you are aware of your attitude, there is enough feedback that control movements should be instinctive. Pitch too high? Push forward until desired attitude reached then trim out force while holding attitude. Unable to reduce pitch with full forward movement? Trim forward until you can. The inverse applies with low pitch.
All of the above requires an instrument scan in IMC, at least of the blue and brown bits of the PFD on a 737 or looking out of the window if you have visual references. It’s the same in a Supercub. If you’ve lost SA in attitude then bad things might happen, regardless of the trimming situation...
One thing that strikes me is that if you are aware of your attitude, there is enough feedback that control movements should be instinctive. Pitch too high? Push forward until desired attitude reached then trim out force while holding attitude. Unable to reduce pitch with full forward movement? Trim forward until you can. The inverse applies with low pitch.
All of the above requires an instrument scan in IMC, at least of the blue and brown bits of the PFD on a 737 or looking out of the window if you have visual references. It’s the same in a Supercub. If you’ve lost SA in attitude then bad things might happen, regardless of the trimming situation...
Otto, you have one key misconception regarding the 737 systems. In any single channel approach a press of TOGA for any reason immediately disconnects the autopilot.
For a hard windshear warning (two tone and WINDSHEAR), the drill is to push TOGA then disconnect everything and apply maximum (full forward stop) thrust.
For an activation of the Predictive Windshear system on the radar a normal go around or the Windshear escape manoeuvre is at the captain's discretion.
We do not know what was attempted but in either cause, the autopilot would be disconnected the moment TOGA was pushed.
A single push of TOGA with the AT engaged annunciates GA in the FMA and the AT commands thrust to provide a rate of climb of 1-2000fpm (typically around 85-90% N1)
A second push of TOGA annunciates N1 in the FMA and you will get all 26k available at which point you will be climbing like a homesick angel at light weights.
For a hard windshear warning (two tone and WINDSHEAR), the drill is to push TOGA then disconnect everything and apply maximum (full forward stop) thrust.
For an activation of the Predictive Windshear system on the radar a normal go around or the Windshear escape manoeuvre is at the captain's discretion.
We do not know what was attempted but in either cause, the autopilot would be disconnected the moment TOGA was pushed.
A single push of TOGA with the AT engaged annunciates GA in the FMA and the AT commands thrust to provide a rate of climb of 1-2000fpm (typically around 85-90% N1)
A second push of TOGA annunciates N1 in the FMA and you will get all 26k available at which point you will be climbing like a homesick angel at light weights.
Join Date: Oct 2008
Location: australia
Posts: 106
Likes: 0
Received 0 Likes
on
0 Posts
Two of the most alarming accidents that involved pre-programmed back trim (system input) during a coupled approach and a subsequent missed approach, both involved in a very short space of time, either the A300 or the A310.
I am going back to the 90's and when I get some time I will find the references (apologies that I am not able to do that at the moment) but it should be relatively easy to find the accident reports.
First one: Nagoya.
Second one: Taipei (Chang Kei Shek as it was at the time).
PIC unable to overcome the pitch trim input following a Manual AP disconnect during the Missed Approach before the aircraft(s) stalled.
I remember seeing both unfortunate wreckages. Plan form on the ground.
I will give you more when I have the time; apologies.
I am going back to the 90's and when I get some time I will find the references (apologies that I am not able to do that at the moment) but it should be relatively easy to find the accident reports.
First one: Nagoya.
Second one: Taipei (Chang Kei Shek as it was at the time).
PIC unable to overcome the pitch trim input following a Manual AP disconnect during the Missed Approach before the aircraft(s) stalled.
I remember seeing both unfortunate wreckages. Plan form on the ground.
I will give you more when I have the time; apologies.
Join Date: Oct 2008
Location: UK
Posts: 361
Likes: 0
Received 0 Likes
on
0 Posts
Jwscud
Boeing would disagree regarding the automatic coupled windshear escape manoeuvre, but as I have no real world, first hand experience, I can only accept their word for it. Please check the QRH Manoeuvres and please don't shoot the messenger.
For the other aspects, we are in full agreement regarding the use of TOGA buttons.
Boeing would disagree regarding the automatic coupled windshear escape manoeuvre, but as I have no real world, first hand experience, I can only accept their word for it. Please check the QRH Manoeuvres and please don't shoot the messenger.
For the other aspects, we are in full agreement regarding the use of TOGA buttons.
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,507
Likes: 0
Received 0 Likes
on
0 Posts
Capn Bloggs offers the most relevant lesson, IMHO,
1. Pitch to attitude.
2. Trim out stick forces.
Being a KISS person, and in stressful situations, I do not have any more mental capacity than to follow this advice. I wonder if some are over complicating it.
What I do notice in the sim is pilots (cadets) who get themselves in odd spots and keep their thumb on the trim wheel firing a full magazine. I encourage 3 shot bursts and then reassess the target (control forces). Another 3 shot burst if necessary. It is not hard to imagine a very high nose attitude, perhaps due to max thrust and an overzealous pull up; full forward elevator control (PFD can be nearly invisible in this scenario) then a full burst of nose down trim, an over speed (flap) and a thrust reduction. The nose will pitch down with much gusto and the required elevator pull force to arrest this plummet is considerable.
Over trimming and agricultural use of thrust is not a healthy combination in B737's.
1. Pitch to attitude.
2. Trim out stick forces.
Being a KISS person, and in stressful situations, I do not have any more mental capacity than to follow this advice. I wonder if some are over complicating it.
What I do notice in the sim is pilots (cadets) who get themselves in odd spots and keep their thumb on the trim wheel firing a full magazine. I encourage 3 shot bursts and then reassess the target (control forces). Another 3 shot burst if necessary. It is not hard to imagine a very high nose attitude, perhaps due to max thrust and an overzealous pull up; full forward elevator control (PFD can be nearly invisible in this scenario) then a full burst of nose down trim, an over speed (flap) and a thrust reduction. The nose will pitch down with much gusto and the required elevator pull force to arrest this plummet is considerable.
Over trimming and agricultural use of thrust is not a healthy combination in B737's.
Qualified Pilot Needed
Full Wings:
That is if you have a qualified pilot in the cockpit. (Remember AF447?)
One thing that strikes me is that if you are aware of your attitude, there is enough feedback that control movements should be instinctive.
After reading all the input here I have come to the conclusion that in all operations where full forward control column is not needed, the system is intuitive. I monitored my own actions more closely than usual a few days ago in a climb that required several seconds of AND trim, and it was intuitive, the force required initially on the control column was quite high but nowhere near full forward, as the stabiliser started to have an effect it was natural to allow the control column to move aft towards the neutral position.
I have never needed full forward control column in the seven or so years that I have been flying the NG, so if tomorrow I did.....would it be intuitive how much AND trim to put in?
I think that if a pilot ends up with nose high, full forward control column, and trimming forward, that the trick would be to stop trimming forward as soon as the nose does start to move in the right direction rather than keep trimming with a determination to get the nose down. It would be quite natural to keep trimming when the attitude slowly drops from 35 nose up to 34...33...32... because the pilot really wants it to hurry up and get to 10 degrees where they feel comfortable, but by the time the nose is coming through 15 degrees the stabiliser is trimmed to require significant back pressure to maintain level flight.
I'd welcome any thoughts on the above, that is my take.
Framer
I have never needed full forward control column in the seven or so years that I have been flying the NG, so if tomorrow I did.....would it be intuitive how much AND trim to put in?
I think that if a pilot ends up with nose high, full forward control column, and trimming forward, that the trick would be to stop trimming forward as soon as the nose does start to move in the right direction rather than keep trimming with a determination to get the nose down. It would be quite natural to keep trimming when the attitude slowly drops from 35 nose up to 34...33...32... because the pilot really wants it to hurry up and get to 10 degrees where they feel comfortable, but by the time the nose is coming through 15 degrees the stabiliser is trimmed to require significant back pressure to maintain level flight.
I'd welcome any thoughts on the above, that is my take.
Framer
Join Date: Oct 2008
Location: australia
Posts: 106
Likes: 0
Received 0 Likes
on
0 Posts
Reference the two accidents I mentioned, here is the wiki link.
I am not saying Wiki is the best source of anything let alone aviation accidents but the links to the reports are there.
https://en.wikipedia.org/wiki/China_Airlines_Flight_140
See also China Airlines flight 676 mentioned and linked at the bottom of the article.
I will say again, these entries are by no means enough for professionals to form a view.
I am not saying Wiki is the best source of anything let alone aviation accidents but the links to the reports are there.
https://en.wikipedia.org/wiki/China_Airlines_Flight_140
See also China Airlines flight 676 mentioned and linked at the bottom of the article.
I will say again, these entries are by no means enough for professionals to form a view.
Join Date: Jun 2006
Location: Brisbane
Posts: 265
Likes: 0
Received 0 Likes
on
0 Posts
framer,
Thank you for that summary of the thread... this is how I read it too, and you have weeded out the distractions.
I've been flying this thing for decades, and this scenario has certainly made me think, and wonder how I would behave in this situation.
What I'm having trouble with, however, is how does a normal go-around (or windshear escape) end up running out of elevator? I've done plenty of go-arounds in the Sim and aircraft, and plenty of windshear escapes (in the Sim only, lucky for me), and I've never come close to full forward elevator.
The only time I can recall getting to full forward elevator was practicing stall recovery after having allowed the autopilot to trim back to stick-shaker, so commencing the recovery with the stab considerably aft.
If full forward elevator happened in a go-around, I would simply reduce thrust (after all, the aircraft was in-trim at lower thrust just prior to the go-around). I certainly wouldn't be flinging it into a 60 degree bank at low level.
If it happened during a windshear escape, which is more likely due to application of maximum thrust, then that would be more interesting, because one wouldn't want to be reducing thrust in windshear. But if a few seconds of forward trim doesn't solve the problem, then I would think another emergency exists (some form of flight control non-normal).
P.S. Otto, Jwscud is correct. Auto-coupled windshear escape is only available for dual channel approach.
Thank you for that summary of the thread... this is how I read it too, and you have weeded out the distractions.
I've been flying this thing for decades, and this scenario has certainly made me think, and wonder how I would behave in this situation.
What I'm having trouble with, however, is how does a normal go-around (or windshear escape) end up running out of elevator? I've done plenty of go-arounds in the Sim and aircraft, and plenty of windshear escapes (in the Sim only, lucky for me), and I've never come close to full forward elevator.
The only time I can recall getting to full forward elevator was practicing stall recovery after having allowed the autopilot to trim back to stick-shaker, so commencing the recovery with the stab considerably aft.
If full forward elevator happened in a go-around, I would simply reduce thrust (after all, the aircraft was in-trim at lower thrust just prior to the go-around). I certainly wouldn't be flinging it into a 60 degree bank at low level.
If it happened during a windshear escape, which is more likely due to application of maximum thrust, then that would be more interesting, because one wouldn't want to be reducing thrust in windshear. But if a few seconds of forward trim doesn't solve the problem, then I would think another emergency exists (some form of flight control non-normal).
P.S. Otto, Jwscud is correct. Auto-coupled windshear escape is only available for dual channel approach.