The Anatomy of a Pitchup!
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Notso Fantastic,
Your comment,
"Can you explain how an aeroplane would have a nose up attitude in an updraft and not rocket upwards?"
The resultant AOA from the forward momentum of the aircraft and the vertical component of the strong updraft, increased the lift and moved the center of lift forward on the swept wing, mechanically pulling the nose up. (Overpowering the tail plane force.) The resultant pitch-up attitude depends on the strength of the vertical updraft and the length of the moment arm, from the c.g. to the tail plane.
The aircraft continued on its projected flight path, in this attitude. Due to this smooth transition in attitude there was little loss of kinetic energy and therefore no imminent stall threat. There was no requirement for any fast reactive action to immediately shove the nose over to return to a normal flight attitude.
Your comment,
"Can you explain how an aeroplane would have a nose up attitude in an updraft and not rocket upwards?"
The resultant AOA from the forward momentum of the aircraft and the vertical component of the strong updraft, increased the lift and moved the center of lift forward on the swept wing, mechanically pulling the nose up. (Overpowering the tail plane force.) The resultant pitch-up attitude depends on the strength of the vertical updraft and the length of the moment arm, from the c.g. to the tail plane.
The aircraft continued on its projected flight path, in this attitude. Due to this smooth transition in attitude there was little loss of kinetic energy and therefore no imminent stall threat. There was no requirement for any fast reactive action to immediately shove the nose over to return to a normal flight attitude.
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The African Dude,
Your comment,
"Aircraft continues at same speed with a higher wing angle of attack - how could they not be generating more lift in this configuration?
Strong Vertical relative wind in updraft.
Your comment,
"Aircraft continues at same speed with a higher wing angle of attack - how could they not be generating more lift in this configuration?
Strong Vertical relative wind in updraft.
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The resultant AOA from the forward momentum of the aircraft and the vertical component of the strong updraft, increased the lift and moved the center of lift forward on the swept wing, mechanically pulling the nose up. (Overpowering the tail plane force.) The resultant pitch-up attitude depends on the strength of the vertical updraft and the length of the moment arm, from the c.g. to the tail plane.
A sudden updraft has a similar AoA effect of instantaneously pitching an aeroplane nose up. Stability is designed into aeroplanes whereby they will restore, and the tailplane will provide a nose down effect.
I repeat, the only way this makes sense (nose up and maintaining altitude) is if you are in a sustained downdraft.
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Did someone say "aerodynamicist"?
OK, let's start at the beginning. The story provided is that an aircraft, in essentially level flight encounters an "updraft", pitches UP some 20-25 degrees with no changes of significance to 'g' or to altitude.
The mechanism of encoutering a shear in the atmosphere are as follows:
As the aircraft enters the region of the gust, the angle of attack (and sideslip, but we're concerned here with a gust in the symmetric plane) are affected, because the aircraft's airspeed and angles are a result of the inertial velocity (which is very slow to change) and the velocity of the air mass, which undergoes an abrupt change.
If an aircraft were to encounter an upwards or downwards moving air mass, the effect would be negligible on airspeed (for most practical combinations of airspeed and gust speed, at least for an airliner type) and significant on angle of attack. The increased movement of the airmass would be manifested as an instantaneous change to the aircraft angle of attack (and would be evident on any AoA metering instrument, such as stall vanes). For an UPDRAFT, there would be an instantaneous increase in the angle of attack; for a DOWNDRAFT there would be an instantaneous decrease in the angle of attack. If one were to assume 50kt instantaneous gust and a 400kt (TAS) one would see an angle of attack change of approximately 7 degrees in the appropriate direction. One would also experience a corresponding 'g' bump as the gust was entered and the 'edge' of the gust passed over the wing. (Since it's a sharp-edged event, the AoA sensors on the nose will 'see' the gust before the wing)
Now, consider the natural aerodynamic response of an aircraft to an instantaneous change in angle of attack. All aircraft are STABLE in flight. Therefore the effect of that stability is for the aircraft to pitch down, or up, so as to reduce the alpha 'spike'. Therefore, an aircraft will aerodynamically pitch DOWN following a sharp-edged updraft, and pitch UP for a downdraft. Any other behaviour would result in an aircraft which had divergent pitch stability and was, essentially, unflyable.
Therefore I simply fail to understand the mechanism you are proposing which would pitch an aircraft nose-up following an updraft.
The centre of lift argument is fallacious - what matters is the neutral point, which will not be moved about by updrafts or downdrafts.
...but, anyway, let's imagine that an aircraft somehow ends up in a 25 degree nose high attitude in level flight relativbe to the earth.
In the absence of any wind component, this implies a 25 degree angle of attack. For any commercial clean wing, this is a stalling angle of attack; there should be stall warnings going off, possibly pushers firing and all kinds of similar activity. None of this is mentioned, therefore one must conclude that the aircraft is at a significantly lower angle of attack. The only way to achieve this is by changing the relative wind to add a significant DOWNDRAFT component, which allows the velocity vector relative to the airmass to more closely approximate the direction of the nose, while still allowing level flight relative to earth. Since this is also the same component consistent with the pitch up behaviour, I see no mystery.
Incidentally, it is theoretically possible for the stalled aircraft to be maintaining level flight in an updraft, if the rate at which the aircraft is falling out of the sky like a brick is matched by the updraft. This is not only inherently unlikely, and would require some rather impressive post-stall manoeuvrability more commonly associated with e.g. Sukhoi-27s at airshows, but still provides no explanation for how the aircraft got to a post-stall attitude in the first place.
Frankly, the reason why "the industry" believes this to be an impossible scenario as described is because it conflicts with the fundamental longitudinal design of every aircraft built.
OK, let's start at the beginning. The story provided is that an aircraft, in essentially level flight encounters an "updraft", pitches UP some 20-25 degrees with no changes of significance to 'g' or to altitude.
The mechanism of encoutering a shear in the atmosphere are as follows:
As the aircraft enters the region of the gust, the angle of attack (and sideslip, but we're concerned here with a gust in the symmetric plane) are affected, because the aircraft's airspeed and angles are a result of the inertial velocity (which is very slow to change) and the velocity of the air mass, which undergoes an abrupt change.
If an aircraft were to encounter an upwards or downwards moving air mass, the effect would be negligible on airspeed (for most practical combinations of airspeed and gust speed, at least for an airliner type) and significant on angle of attack. The increased movement of the airmass would be manifested as an instantaneous change to the aircraft angle of attack (and would be evident on any AoA metering instrument, such as stall vanes). For an UPDRAFT, there would be an instantaneous increase in the angle of attack; for a DOWNDRAFT there would be an instantaneous decrease in the angle of attack. If one were to assume 50kt instantaneous gust and a 400kt (TAS) one would see an angle of attack change of approximately 7 degrees in the appropriate direction. One would also experience a corresponding 'g' bump as the gust was entered and the 'edge' of the gust passed over the wing. (Since it's a sharp-edged event, the AoA sensors on the nose will 'see' the gust before the wing)
Now, consider the natural aerodynamic response of an aircraft to an instantaneous change in angle of attack. All aircraft are STABLE in flight. Therefore the effect of that stability is for the aircraft to pitch down, or up, so as to reduce the alpha 'spike'. Therefore, an aircraft will aerodynamically pitch DOWN following a sharp-edged updraft, and pitch UP for a downdraft. Any other behaviour would result in an aircraft which had divergent pitch stability and was, essentially, unflyable.
Therefore I simply fail to understand the mechanism you are proposing which would pitch an aircraft nose-up following an updraft.
The centre of lift argument is fallacious - what matters is the neutral point, which will not be moved about by updrafts or downdrafts.
...but, anyway, let's imagine that an aircraft somehow ends up in a 25 degree nose high attitude in level flight relativbe to the earth.
In the absence of any wind component, this implies a 25 degree angle of attack. For any commercial clean wing, this is a stalling angle of attack; there should be stall warnings going off, possibly pushers firing and all kinds of similar activity. None of this is mentioned, therefore one must conclude that the aircraft is at a significantly lower angle of attack. The only way to achieve this is by changing the relative wind to add a significant DOWNDRAFT component, which allows the velocity vector relative to the airmass to more closely approximate the direction of the nose, while still allowing level flight relative to earth. Since this is also the same component consistent with the pitch up behaviour, I see no mystery.
Incidentally, it is theoretically possible for the stalled aircraft to be maintaining level flight in an updraft, if the rate at which the aircraft is falling out of the sky like a brick is matched by the updraft. This is not only inherently unlikely, and would require some rather impressive post-stall manoeuvrability more commonly associated with e.g. Sukhoi-27s at airshows, but still provides no explanation for how the aircraft got to a post-stall attitude in the first place.
Frankly, the reason why "the industry" believes this to be an impossible scenario as described is because it conflicts with the fundamental longitudinal design of every aircraft built.
Excellent topic, y'all.
There is a small section in our manual (swept-wing, twin-turbofan) which claims that in some severe turbulence situations, it might be best to not just engage the autopilot, but switch one of the knobs to pitch hold, in order to avoid chasing airspeed by moving the yoke forwards and back.
I've never read anything else about this 'pitch hold', nor seen other (captains years ago) pilots use it, nor seen it discussed in any systems review or sim briefing etc. Of course (I) we've never been in any turbulence worse than 'strong' moderate
, fortunately. I would rather be in a bit of moderate for a short while than have these damned computerized systems tests in the future 
.
There is a small section in our manual (swept-wing, twin-turbofan) which claims that in some severe turbulence situations, it might be best to not just engage the autopilot, but switch one of the knobs to pitch hold, in order to avoid chasing airspeed by moving the yoke forwards and back.
I've never read anything else about this 'pitch hold', nor seen other (captains years ago) pilots use it, nor seen it discussed in any systems review or sim briefing etc. Of course (I) we've never been in any turbulence worse than 'strong' moderate
, fortunately. I would rather be in a bit of moderate for a short while than have these damned computerized systems tests in the future .
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Mad Scientist- that is my reading of the situation and seems to be broadly in line with what I was trying to say.
My worst experience with this sort of situation was flying into Genoa in a 737-200. Joining the hold in some violent CBs, as we were going around the holding pattern, we were going from very strong downdrafts to updrafts at each end. Speed was falling back to 200 kts clean with full power on at one end whilst we struggled through the downdraft ( I actually saw about 195 with full power), and as we moved to the other end, speed was increasing and the thrust levers were coming back to idle at 290 kts. It was an extraordinary situation. We managed 2 holds in serious turbulence before chickening out and diverting to Milan Linate.
My worst experience with this sort of situation was flying into Genoa in a 737-200. Joining the hold in some violent CBs, as we were going around the holding pattern, we were going from very strong downdrafts to updrafts at each end. Speed was falling back to 200 kts clean with full power on at one end whilst we struggled through the downdraft ( I actually saw about 195 with full power), and as we moved to the other end, speed was increasing and the thrust levers were coming back to idle at 290 kts. It was an extraordinary situation. We managed 2 holds in serious turbulence before chickening out and diverting to Milan Linate.
Last edited by Notso Fantastic; 15th Jan 2005 at 09:56.
M(flt)S Using your excellent post as a basis, could you or any one else provide an explanation or hypothesis for the incident that I described earlier. I could not establish whether the aircraft entered an up or down draft, but it pitched up and climbed rapidly. Whatever the phenomenon, there was a period where full forward stick only just balanced the pitching moment – this could be a manifestation of instability.
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alf5071h - this is all pure speculation without the data but....
If the aircraft were at, say, 15 deg nose up pitch attitude and approx zero AoA in the climb before the incident, and were to pitch up to 30 deg AoA instantaneously, that's 15 deg AoA. To achieve that with the controls would take a great deal of nose-up pitch command - in the absence of such a command the aircraft would naturally be very quick to return to the trim near-zero AoA value.
If you were applying nose down-pitch command, but the pitch attitude were not changing, then I would conclude that you were in a stabilised condition. This would actually imply that your AoA was more negative during the event than prior to it, even though your pitch attitude was more positive. The simplest explanation for that is a downdraft.
Now, to address the altitude change - the aircraft went from FL130 to FL180 in one minute. One of the first things I would check with the data would be your geometric altitude, not your pressure altitude; in a significant atmospheric disturbance, I'm not sure I trust pressure altitude to be consistent through the event. If the shear/gust/downdraft were also associated with a significant pressure gradient, some or all of the apparent altitude change might have been due to pressure, not altitude. You mention it was at night, so a geometric altitude variation would not be so apparent.
Those would be my initial comments; as I mentioned, there would be a lot going on you might not be aware of, and only looking at the FDR traces would really resolve some of it.
If the aircraft were at, say, 15 deg nose up pitch attitude and approx zero AoA in the climb before the incident, and were to pitch up to 30 deg AoA instantaneously, that's 15 deg AoA. To achieve that with the controls would take a great deal of nose-up pitch command - in the absence of such a command the aircraft would naturally be very quick to return to the trim near-zero AoA value.
If you were applying nose down-pitch command, but the pitch attitude were not changing, then I would conclude that you were in a stabilised condition. This would actually imply that your AoA was more negative during the event than prior to it, even though your pitch attitude was more positive. The simplest explanation for that is a downdraft.
Now, to address the altitude change - the aircraft went from FL130 to FL180 in one minute. One of the first things I would check with the data would be your geometric altitude, not your pressure altitude; in a significant atmospheric disturbance, I'm not sure I trust pressure altitude to be consistent through the event. If the shear/gust/downdraft were also associated with a significant pressure gradient, some or all of the apparent altitude change might have been due to pressure, not altitude. You mention it was at night, so a geometric altitude variation would not be so apparent.
Those would be my initial comments; as I mentioned, there would be a lot going on you might not be aware of, and only looking at the FDR traces would really resolve some of it.
Couldn't alf5701h's excursion have been a strong horizontal gust? A sudden increase in headwind would initiate a phugoid, though you may have brought it under control before it became apparent as such. If the gust decayed gradually, it might not have been noticeable.
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Phugoid is too long period a motion, typically it's measured in minutes, this was over in a minute or so it seems.
A strong headwind would indeed have caused increased lift at the fixed AoA. But there should have been no difficulty whatsoever in pitching the nose down to maintain altitude, since if anything the increased airspeed would have provided more absolute tailplane/elevator pitch authority. So the comment about running out of pitch control seems to work against that.
A strong headwind would indeed have caused increased lift at the fixed AoA. But there should have been no difficulty whatsoever in pitching the nose down to maintain altitude, since if anything the increased airspeed would have provided more absolute tailplane/elevator pitch authority. So the comment about running out of pitch control seems to work against that.
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Mad (Flt) Scientist
Great post- agree with it all. The CAB report on the crash of NW 705 (described in the opening post of this thread from wsherif1) seems to agree as well:
But what does this mean? Does it mean that the initial response is nose down followed by nose up?
-----------------------------------------------------
Could you walk us through the traces below from the same report?
The initial part of the top (altitude) trace is the normal climb, which then increases (according to the text of the report) to three and a half times the normal rate of climb.
I assume that this increased rate of climb is due to an up draught.
The next trace shows a falling air speed - not surprising.
The next traces are deduced from FDR data but are not direct traces.
The first shows a PITCH UP increasing from about 4 to 20 degrees during this climb.
This is not a "weather cocking down into the up draught", but might be what the CAB called “the ultimate effect of the updraft is an altitude and nose up attitude increase“.
The last trace shows an initially unchanging angle of attack.
---------------------------
So does an updraft initially induce nose down quickly followed by nose up, or what?
The pitch trace shows no sign of nose down, with a climb rate three and a half times normal.
Signed, Puzzled.
------------------------------
Ignition Override
The same report contained strong words of advice to use the attitude indicator as the primary instrument in turbulence, and even then to go easy on the controls. They didn‘t seem to like auto pilots much.:
"From all the evidence available to the Board, it is abundantly clear that flight on instruments in heavy turbulence can present a difficult problem to any pilot who departs too far from the recommended practice of using the attitude indicator as the main reference instrument for maintaining control. If the pilot places undue emphasis on any other flight instrument during his normal scan routine, a serious miscue with drastic consequences can occur. Similarly, attempts to maintain "perfect" attitude control can be equally hazardous, because of the high loadings induced, the danger of over controlling by the use of large control displacements, and the possibility of inducing an undesirable oscillatory motion of the aircraft. "Loose" attitude control, or moderate counteracting control inputs, appears to be the best method of counteracting the effects of heavy turbulence. ………… Little is gained by trying to maintain rigid. attitude control since this can produce excessive aircraft loadings without appreciably affecting the altitude and airspeed excursions that occur during severe encounters. Large pitch attitudes of 40 degrees nose up can occur in severe turbulence but moderate counteracting elevator inputs will prevent excessive speed reductions that could result in a stall. The use of the autopilot on Manual Mode offers some advantages but considerable stabilizer trim activity can occur in some types of' turbulence and could present a serious danger if the autopilot was disengaged either deliberately or inadvertently at a time when the trim varied appreciably from the in-trim setting .”
Cheers,
Great post- agree with it all. The CAB report on the crash of NW 705 (described in the opening post of this thread from wsherif1) seems to agree as well:
But what does this mean? Does it mean that the initial response is nose down followed by nose up?
-----------------------------------------------------
Could you walk us through the traces below from the same report?
The initial part of the top (altitude) trace is the normal climb, which then increases (according to the text of the report) to three and a half times the normal rate of climb.
I assume that this increased rate of climb is due to an up draught.
The next trace shows a falling air speed - not surprising.
The next traces are deduced from FDR data but are not direct traces.
The first shows a PITCH UP increasing from about 4 to 20 degrees during this climb.
This is not a "weather cocking down into the up draught", but might be what the CAB called “the ultimate effect of the updraft is an altitude and nose up attitude increase“.
The last trace shows an initially unchanging angle of attack.
---------------------------
So does an updraft initially induce nose down quickly followed by nose up, or what?
The pitch trace shows no sign of nose down, with a climb rate three and a half times normal.
Signed, Puzzled.
------------------------------
Ignition Override
The same report contained strong words of advice to use the attitude indicator as the primary instrument in turbulence, and even then to go easy on the controls. They didn‘t seem to like auto pilots much.:
"From all the evidence available to the Board, it is abundantly clear that flight on instruments in heavy turbulence can present a difficult problem to any pilot who departs too far from the recommended practice of using the attitude indicator as the main reference instrument for maintaining control. If the pilot places undue emphasis on any other flight instrument during his normal scan routine, a serious miscue with drastic consequences can occur. Similarly, attempts to maintain "perfect" attitude control can be equally hazardous, because of the high loadings induced, the danger of over controlling by the use of large control displacements, and the possibility of inducing an undesirable oscillatory motion of the aircraft. "Loose" attitude control, or moderate counteracting control inputs, appears to be the best method of counteracting the effects of heavy turbulence. ………… Little is gained by trying to maintain rigid. attitude control since this can produce excessive aircraft loadings without appreciably affecting the altitude and airspeed excursions that occur during severe encounters. Large pitch attitudes of 40 degrees nose up can occur in severe turbulence but moderate counteracting elevator inputs will prevent excessive speed reductions that could result in a stall. The use of the autopilot on Manual Mode offers some advantages but considerable stabilizer trim activity can occur in some types of' turbulence and could present a serious danger if the autopilot was disengaged either deliberately or inadvertently at a time when the trim varied appreciably from the in-trim setting .”
Cheers,
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Can I throw a question in here for the technically-minded?
Initially, Notso's thesis made perfect sense to me. However, it occurs to me that, in most modern aircraft, the centre of gravity is aft the centre of lift (thus necessitating a net downforce by the tailplane).
A strong updraft would act primarily on the CofG, n'est ce pas? thus making the initial response by the aircraft a nose-down pitch.
Or am I talking a load of whatsits?
Initially, Notso's thesis made perfect sense to me. However, it occurs to me that, in most modern aircraft, the centre of gravity is aft the centre of lift (thus necessitating a net downforce by the tailplane).
A strong updraft would act primarily on the CofG, n'est ce pas? thus making the initial response by the aircraft a nose-down pitch.
Or am I talking a load of whatsits?
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Lockheed at the head of the pack with design...
...again.
Yes, Ignition Override, 'pitch hold' works as advertised, altho on the TriStar, it was called 'turbulence mode'.
I have personally used same on a number of occasions, and the pitch excursions are indeed kept to a minimum.
Worked like a charm.
Yes, Ignition Override, 'pitch hold' works as advertised, altho on the TriStar, it was called 'turbulence mode'.
I have personally used same on a number of occasions, and the pitch excursions are indeed kept to a minimum.
Worked like a charm.
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The way I see it, a pitch changing effect on the CofG would require significant (and sustained) vertical acceleration to cause any effect of acting as a lever around the centre of lift. The CofG and centre of lift are very close and I can't see an updraft having the sustained effect to cause a pitch change on such a mass- there is just not enough lever arm moment. We're told there is not much change in altitude, so the acceleration force acting on the CofG is nothing more than momentary. I think the weathercocking of the tailplane is overriding.
I think the effect we see in the flight recorder traces is an encounter with a downdraft causing pitch up. This is countered with large control inputs nose down, just as the plane comes out of the downdraft into the surrounding updraft. Combine the effects of weathercocking again, but nose down this time, with a strong control input which is already held nose down, and that explains the violently large and rapid nose down pitch. Did it exceed structural limits and break up? It obviously goes into strong negative 'g' territory from 12.20 onwards. I can't see anything more complicated than that scenario.
I've found the accident report now. I thought I didn't remember this one! The inflight structural break up explains the damage to the artificial horizons- it's not possible it was structurally sound and pitching 90 degrees nose down! There is no way the integrity of the fuselage could be partially maintained if it pitched enough to damage the AH stops- sadly I think the spinning and pitching that occured to the cockpit as it disintegrated and after caused the violent movement that damaged the stops. We're looking for mysterious effects that just aren't there because of the faulty premise given to us earlier.
I think the effect we see in the flight recorder traces is an encounter with a downdraft causing pitch up. This is countered with large control inputs nose down, just as the plane comes out of the downdraft into the surrounding updraft. Combine the effects of weathercocking again, but nose down this time, with a strong control input which is already held nose down, and that explains the violently large and rapid nose down pitch. Did it exceed structural limits and break up? It obviously goes into strong negative 'g' territory from 12.20 onwards. I can't see anything more complicated than that scenario.
I've found the accident report now. I thought I didn't remember this one! The inflight structural break up explains the damage to the artificial horizons- it's not possible it was structurally sound and pitching 90 degrees nose down! There is no way the integrity of the fuselage could be partially maintained if it pitched enough to damage the AH stops- sadly I think the spinning and pitching that occured to the cockpit as it disintegrated and after caused the violent movement that damaged the stops. We're looking for mysterious effects that just aren't there because of the faulty premise given to us earlier.
Last edited by Notso Fantastic; 15th Jan 2005 at 22:52.
Phugoid is too long period a motion, typically it's measured in minutes, this was over in a minute or so it seems.
The traces in PickyPerkins's post look mostly like phugoid motion, don't they? If you picture the airspeed at 11:50 as an equilibrium value, a sudden increase with a maximum at about 12:00 leaves the aircraft with excess lift. What follows is broadly, constant AOA, with altitude increasing, airspeed decreasing 180 degrees out of phase, pitch attitude leading the altitude by 90 degrees. Thus it looks like the phugoid will have gone through a half cycle by about 12:25.
However, it looks like the crew intervenes at just after 12:20 with a great big downward punt on the controls, pushing the nose, and therefore AOA, down by 15 degrees. And they did that at just the wrong time, because the nose is about to go back down of its own accord, so instead of halting the oscillation, they exacerbate it.
Of course, since the modes are coupled, it's more complicated than that, but that looks like the broad idea.
How do the numbers work? An airspeed excursion from 325 KTAS to 365 KTAS (250 KIAS to 280 KIAS) is "worth" a bit less than 1200 ft of energy. It looks like the amplitude of the excursion was rather more than that, but that may be disguised by the aircraft being in a climb to start with. Or it may be that the airspeed started below 250 KIAS -- we don't know what went on before 11:50.
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We;re not talking phugoids here. The weather conditions here were typical Florida storm activity- no doubt severe turbulence with powerful up and down drafts. I believe any phugoid effect would have been obliterated by the immediate vertical wind components.
That's not what the data says, NF. An updraft or downdraft would have resulted in spike in AOA, and a sharp change in pitch attitude as it returned to its trimmed value, over the timescale of that mode which might be a few seconds at most.
No doubt that was happening on a small scale, contributing to the confusion that must have it very hard for the crew. But I don't see how you can dismiss significant horizontal gusts in those conditions.
No doubt that was happening on a small scale, contributing to the confusion that must have it very hard for the crew. But I don't see how you can dismiss significant horizontal gusts in those conditions.
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Where is the data support for gusts? Speed changes don't seem very great until the aircraft departs. This is an early 60s accident with very primitive flight recording. The conditions were serious Cbs. The main effect is violent vertical drafts. I think there is absolutely no evidence to support a hypothesis that horizontal gusts played any part whatsoever. This was an aeroplane torn apart by serious vertical acceleration probably coupled with large control inputs. Since those days, we've learnt to 'ride' it rather than try and maintain attitude/altitude.
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For those wanting to see the full report on the crash of NW 705, a pdf version can be seen at
http://www.avsaf.org/reports/US_repo...oeing-720B.pdf
If this link does not work for you, go to
http://www.avsaf.org/reports/US_reports
then click on
1963
then click on
Feb. 12 1963
and you will get to the same place.
Cheers,
http://www.avsaf.org/reports/US_repo...oeing-720B.pdf
If this link does not work for you, go to
http://www.avsaf.org/reports/US_reports
then click on
1963
then click on
Feb. 12 1963
and you will get to the same place.
Cheers,
