TNFlygirl crash analysis
Quote:
"Was Juan Browne right that holding UP/DN does nothing because the buttons are "momentary action" or do they continuusly change the ATT mode pitch reference?"
Near the start of the video Juan B explains that in this particular aircraft the autopilot is NOT connected to the Trim Wheell at all. There is no electric trim, only manual.
On the control yoke there are no trim buttons, only an Autopilot disconnect switch.
So the Autopilot only lights a light when it wants a Trim change, but the Pilot must implement the change manually with the Trim Wheel. Sadly, the pilot does not seem to have grasped this.
IB
"Was Juan Browne right that holding UP/DN does nothing because the buttons are "momentary action" or do they continuusly change the ATT mode pitch reference?"
Near the start of the video Juan B explains that in this particular aircraft the autopilot is NOT connected to the Trim Wheell at all. There is no electric trim, only manual.
On the control yoke there are no trim buttons, only an Autopilot disconnect switch.
So the Autopilot only lights a light when it wants a Trim change, but the Pilot must implement the change manually with the Trim Wheel. Sadly, the pilot does not seem to have grasped this.
IB
Quote:
"Was Juan Browne right that holding UP/DN does nothing because the buttons are "momentary action" or do they continuusly change the ATT mode pitch reference?"
Near the start of the video Juan B explains that in this particular aircraft the autopilot is NOT connected to the Trim Wheell at all. There is no electric trim, only manual.
On the control yoke there are no trim buttons, only an Autopilot disconnect switch.
So the Autopilot only lights a light when it wants a Trim change, but the Pilot must implement the change manually with the Trim Wheel. Sadly, the pilot does not seem to have grasped this.
IB
"Was Juan Browne right that holding UP/DN does nothing because the buttons are "momentary action" or do they continuusly change the ATT mode pitch reference?"
Near the start of the video Juan B explains that in this particular aircraft the autopilot is NOT connected to the Trim Wheell at all. There is no electric trim, only manual.
On the control yoke there are no trim buttons, only an Autopilot disconnect switch.
So the Autopilot only lights a light when it wants a Trim change, but the Pilot must implement the change manually with the Trim Wheel. Sadly, the pilot does not seem to have grasped this.
IB
Do you have anything to add to the explanation provided in Pilot's Operating Manual - https://wfc-hpn.org/wp-content/uploa...toPilotPOH.pdf
I fly a baron currently, which is equipped with a century 41 (nearly the same, but with electric pitch)
the video was incorrect with regard to how one moves between “ALT” and “ATT”.
One must actually push the appropriate button to change modes. If the “UP” or “Down” button is pushed while in the “ALT” mode, the plane will make a furtive effort to go in the desired direction, but will remain in the “ALT” mode.
Furthermore, while the up and down buttons are technically momentary, the rate of climb or descent is not discretely selectable. One simply pushes the switch, and counts. Supposedly, after 2 or 3 seconds (during which not much happens) the rate of climb or descent is roughly around 100ft/min for each additional minute. (But it’s not really, it actually just sort of does whatever it wants to do, and requires constant adjustment as altitude/airspeed changes. One cannot use the autopilot without employing either the “ATT” or “ALT” mode.
In my particular iteration, I can put the Autopilot in “HDG” Mode, and engage the GNSS add-on function which will provide GPS tracking and roll steer, but no VNAV. Trying to fly a glide slope on an RPV with the “UP/Down” buttons is essentially impossible due to the inaccuracy and lag inherent in the system.
Cessna, Bendix, Stec and Garmin had a much better idea….
the video was incorrect with regard to how one moves between “ALT” and “ATT”.
One must actually push the appropriate button to change modes. If the “UP” or “Down” button is pushed while in the “ALT” mode, the plane will make a furtive effort to go in the desired direction, but will remain in the “ALT” mode.
Furthermore, while the up and down buttons are technically momentary, the rate of climb or descent is not discretely selectable. One simply pushes the switch, and counts. Supposedly, after 2 or 3 seconds (during which not much happens) the rate of climb or descent is roughly around 100ft/min for each additional minute. (But it’s not really, it actually just sort of does whatever it wants to do, and requires constant adjustment as altitude/airspeed changes. One cannot use the autopilot without employing either the “ATT” or “ALT” mode.
In my particular iteration, I can put the Autopilot in “HDG” Mode, and engage the GNSS add-on function which will provide GPS tracking and roll steer, but no VNAV. Trying to fly a glide slope on an RPV with the “UP/Down” buttons is essentially impossible due to the inaccuracy and lag inherent in the system.
Cessna, Bendix, Stec and Garmin had a much better idea….
Either the Century 41 behaves differently from the Century 2000 or one of the descriptions is wrong. At least you have confirmed that continuous press of UP/DN changes the pitch reference for the Century 41 so thanks for that.
I would expected that disconnecting for the transition to climb or descent and then re-engaging in ATT mode when in trim would give far better results that trying to establish a climb or descent by changing ATT reference.
As for rate of response - The Century 2000 manual says:
"*PITCH AXIS:
Command Attitude - 0.7° per second attitude change.
Gust Recovery - Maximum rate consistent with passenger comfort.
Maximum System Capability - 2.4° per second ."
I assume that this means holding UP or DN will change the ATT reference at 0.7 degrees/second. What this does to vertical speed will depend on power and pitch trim. Unlike the Garmin system I fly the Century 2000 has no closed loop VS mode.
I'm curious.
Has anyone suggested that unless the AP disconnect switch was inoperative and there was a question as to how ANYTHING worked on the AP, that there was always the option to go manual, deal with the problem and/or remain manually flying the airplane?
Also, has anyone wondered why the instructor didn't change the lesson plan (on the fly) to deal with the remedial education required concerning the student and the AP?
I admit I haven't been deeply engrossed in this incident and this specific thread but these factors seem extremely pertinent to me.
Have I missed something?
Dudley Henriques
Has anyone suggested that unless the AP disconnect switch was inoperative and there was a question as to how ANYTHING worked on the AP, that there was always the option to go manual, deal with the problem and/or remain manually flying the airplane?
Also, has anyone wondered why the instructor didn't change the lesson plan (on the fly) to deal with the remedial education required concerning the student and the AP?
I admit I haven't been deeply engrossed in this incident and this specific thread but these factors seem extremely pertinent to me.
Have I missed something?
Dudley Henriques
The pitch modifier function of the Century 41 appears to be significantly different from the Century 2000.
Last edited by EXDAC; 19th Dec 2023 at 14:29.
Speaking as a retired avionics systems engineer with some experience of automatic flight controls development and certification - I simply wanted to know how this autopilot system was intended to work and whether the comments made by Juan Browne were valid.
Speaking as a pilot and CFII - Yes, that was the obvious action that should have been taken. It's hard for me to imagine how a pilot would allow a flight control system to kill them in day VMC.
Speaking as a retired avionics systems engineer with some experience of automatic flight controls development and certification - I simply wanted to know how this autopilot system was intended to work and whether the comments made by Juan Browne were valid.
Speaking as a retired avionics systems engineer with some experience of automatic flight controls development and certification - I simply wanted to know how this autopilot system was intended to work and whether the comments made by Juan Browne were valid.
My questions were more general in nature. Simply curious.
Dudley Henriques
From Exdac:
"Your answer does not comment on the function of the UP/DN switches. Why did you quote my question?"
Ok, sorry, I misunderstood/misread your comment.
I simply wanted to clarify that the plane in question did not have electric autotrim, and therefore the Up/DN buttons only try to change the plane's attitude, they do not necessarily cause climb/descent. Perhaps the buttons should be labelled "Nose Up" and "Nose Down" for greater clarity? Although I would think that any competent PPL pilot would understand this anyway.
Additionally, there are 2 annunciator lights on the Autopilot panel that read "Trim Up" and "Trim down", but these are not indicators of what the control surfaces are doing, instead they are instructions to the pilot to implement the trimming manually. They light up when the autopilot calculates that a trim adjustment is necessary, and go off when the pilot has responded, and successfuly altered the pitch attitude.
As Juan says, tragically the pilot does not seem to have grasped any of this.
Anyway, sorry again for my misunderstanding, I hope we are "cool" !
IB
"Your answer does not comment on the function of the UP/DN switches. Why did you quote my question?"
Ok, sorry, I misunderstood/misread your comment.
I simply wanted to clarify that the plane in question did not have electric autotrim, and therefore the Up/DN buttons only try to change the plane's attitude, they do not necessarily cause climb/descent. Perhaps the buttons should be labelled "Nose Up" and "Nose Down" for greater clarity? Although I would think that any competent PPL pilot would understand this anyway.
Additionally, there are 2 annunciator lights on the Autopilot panel that read "Trim Up" and "Trim down", but these are not indicators of what the control surfaces are doing, instead they are instructions to the pilot to implement the trimming manually. They light up when the autopilot calculates that a trim adjustment is necessary, and go off when the pilot has responded, and successfuly altered the pitch attitude.
As Juan says, tragically the pilot does not seem to have grasped any of this.
Anyway, sorry again for my misunderstanding, I hope we are "cool" !
IB
During these altitude fluctuations, the controller twice provided instructions to the pilot to contact the Memphis Air Route Traffic Control Center; however, neither of the instructions were acknowledged by the pilot. During the final moments of the flight, a faint communication from the pilot stating the airplane’s registration and “Debonaire” followed by an emergency declaration and an unintelligible word. About 60 seconds later, a faint and largely unintelligible transmission from the passenger was transmitted.
Aviation Investigation Preliminary Report - N5891J
Aviation Investigation Preliminary Report - N5891J
Forget all about modern autopilots to understand what happened.
This ancient autopilot system and its limitations is easy to understand, if you know what it physically does: It manipulates the yoke with motorized inputs to it like the pilots arm would do, which in turn affects the primary flight control surfaces. It basically is a substitute for the pilots hand on the yoke. It has no control over power and trim, does not control speed, altitude, or vertical speed. It only controls the attitude of the aircraft as long as it is able to do so.
Imagine you are flying without trimming, you turn, climb, accelerate and decelerate, climb and descent without trimming, without adjusting power. Imagine the forces on the yoke and the influence to the aircraft performance in relation to speed and power. That describes the limited capability of that ancient autopilot only in part, because while a pilot should take note of all the outcome, this autopilot will only recognize the force it needs to control the pitch and request a change by the trim lights "up" and "down".
Looking at the videos it is imho obvious that this pilot lacked the necessary system knowledge and at the final stage general airmanship.
Imagine you are flying without trimming, you turn, climb, accelerate and decelerate, climb and descent without trimming, without adjusting power. Imagine the forces on the yoke and the influence to the aircraft performance in relation to speed and power. That describes the limited capability of that ancient autopilot only in part, because while a pilot should take note of all the outcome, this autopilot will only recognize the force it needs to control the pitch and request a change by the trim lights "up" and "down".
Looking at the videos it is imho obvious that this pilot lacked the necessary system knowledge and at the final stage general airmanship.
RetiredF4:
Perfect Post.
That is what I have been trying to say in 2 posts, but not nearly as clearly as your one!
It is incredible to me that anyone would fly a plane for many, many flights, but not have any basic understanding of pitch/power, apparently. Surely it easy to grasp that climbing in a plane is like going up a hill in a car, and therefore more power is required, so you press the accelerator?
And I got the impression from her videos that she thought that when the "Trim Up/DN" lights were illuminated, the autopilot was trimming the plane for her, which of course it could not, because the plane lacked electric trim.
IB
Perfect Post.
That is what I have been trying to say in 2 posts, but not nearly as clearly as your one!
It is incredible to me that anyone would fly a plane for many, many flights, but not have any basic understanding of pitch/power, apparently. Surely it easy to grasp that climbing in a plane is like going up a hill in a car, and therefore more power is required, so you press the accelerator?
And I got the impression from her videos that she thought that when the "Trim Up/DN" lights were illuminated, the autopilot was trimming the plane for her, which of course it could not, because the plane lacked electric trim.
IB
This ancient autopilot system and its limitations is easy to understand, if you know what it physically does: It manipulates the yoke with motorized inputs to it like the pilots arm would do, which in turn affects the primary flight control surfaces. It basically is a substitute for the pilots hand on the yoke. It has no control over power and trim, does not control speed, altitude, or vertical speed. It only controls the attitude of the aircraft as long as it is able to do so.
Join Date: Aug 2000
Location: Near Stuttgart, Germany
Posts: 1,096
Likes: 0
Received 1 Like
on
1 Post
And a proper approach mode including glideslope. It is not the dumb kind of "wing leveler" device found in some light aircraft. And the UP and DOWN buttons acting on the attitude and not on the vertical speed is not unique to this autopilot either. The only unusual feature are the trim lights that prompt the pilot to trim manually. In similar autopilots the trim lights illuminate when the autopilot acts on the trim. As was written above, the accident pilot seems not to have been aware of that. Flying on autopilot for some time, possibly with power and altitude changes, may leave the aircraft in an out-of-trim condition outside the force that the autopilot servos can handle. When the autopilot subsequently disengages, a rapid change in pitch will follow as a consequence. Everyone who has flown old(ish) light aircraft for some time will sooner or later encounter this situation. Lightplane autopilot control forces are in the order of 15 to 25 force pounds, like lifting a bucket of water. Apart from the startle effect and possible disorientation in instrument meteorological conditions they are easily controllable manually. Especially in this flight with two pilots on board.
Let's hope the data cards of the video cameras are not damaged by the fire as they will certainly reveal what exactly led to this accident.
Let's hope the data cards of the video cameras are not damaged by the fire as they will certainly reveal what exactly led to this accident.