TNFlygirl crash analysis
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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.
Looking at the videos it is imho obvious that this pilot lacked the necessary system knowledge and at the final stage general airmanship.
Looking at the videos it is imho obvious that this pilot lacked the necessary system knowledge and at the final stage general airmanship.
Your criticism of the autopilot system is probably and understandably from a modern Jet perspective. However ancient autopilots of the era are not that far removed from modern autopilot function in non-fadec piston engine aircraft, in that they do not control power. This particular autopilot did control altitude, attitude and glideslope, but not trim (which may well have been the cause of the accident), but many autopilots of the era did.. as they incorporated electric trim. This Century 2000 unit was designed for aircraft with no electric trim fitted.
Leaving aside for a moment that the autopilot was probably 35 years old and modern advances in digital electronics, reliability, weight savings have changed the game to some extent.. the function is not that much different if you understand how the thing works.
A reasonably similar fatal accident occurred with a PC12 in February last year with the latest of tech.
In ALT mode the AP attempts to maintain the difference between the altitude and the altitude target at zero. It is controlling the aircraft altitude. How it does that, and the concept of inner and outer control loops, is probably out of scope here.
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Forget about the autopilot for a moment. How do you transition from hand flown altitude hold to hand flown VS target climb or descent?
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There seem to be several people posting here who do not understand the proper response to illumination of the trim annunciators. Only after setting appropriate power for the desired climb or descent vertical speed should a trim annunciator be taken as an indication to change pitch trim.
Forget about the autopilot for a moment. How do you transition from hand flown altitude hold to hand flown VS target climb or descent?
Forget about the autopilot for a moment. How do you transition from hand flown altitude hold to hand flown VS target climb or descent?
I would add power.
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I think the correct answer is: do both. Follow the indication of the trim indicator to make life easier for the autopilot and add power if you observe the airspeed decreasing.
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It has been thirty years since I flew a Rockwell Commander 112a with a Century autopilot. It had electric elevator and rudder trim. In ATL only small MP adjustments were required.
I have no modern jet experience, as my nickname states I flew Phantom F4 aircraft, over 3.000 hours, 1/3 of them instructing and evaluating. The most civilian modern jet Cockpit I ever occupied as a pilot was a Caravelle simulator for ATPL training and following successful check ride.
The autopilot of the Phantom was similar in the limitations as the century series one and could kill you if operated without the necessary oversight and control. Especially the "Altitude hold" had its traps.
That brings me back to responses like
"it controls altitude", it could cause out of trim conditions....."
Afaik from the manual and the informations provided this aircraft had no electric trim and no auto throttle, all the inputs from the autopilot acted directly onto the yoke. If the pilot does not trim manually, then the trim stays at its position where the pilot had put it prior engaging the autopilot. Same with the power. An out of trim situation is caused when the aircraft parameters ( TAS, pressure altitude, CG to name a few) are changed and the trim is not adjusted manually and / or the deviating parameter is not corrected to the original value.
There might be a misconception about using the term "control" and it might be on my side, as I'm no native english speaking person. Only an autopilot controlling auto trim and auto throttle could control altitude alone over time. Such a system needs a lot if inputs and feed back loops the used autopilot in the discussed accident aircraft didn't have. Sure an average pilot can use this autopilot to control the altitude without auto trim and auto thrust, the autopilot alone can't and here the knowledge of the pilot looks amiss.
Going back to my original post, this autopilot only acts on the yoke, operating power and trim are out of its reach as it would be to a pilot whose hands were tied to the yoke. Would the pilot have known this, she would have controlled speed and altitude, the traces show no sign of such action, to the contrary. The oscillation deviation of speed and altitude increases in each cycle, until hitting the ground.
There is a time to be sorry, but we only learn from the truth. Not saying though that it will be my truth. Enough said, there will be those who understand, and those who will have to make their own way of learning.
Fly safe, merry Christmas and a peaceful year 2024.
Last edited by RetiredF4; 21st Dec 2023 at 06:00.
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.
He was not a rated pilot. My understanding is that he liked to accompany his daughter and she felt more comfortable with him aboard. From the few videos I watched after the crash, she seemed to rely upon him quite a bit to assist with looking outside while she was heads-down and for general support with the aircraft. There were a few radio calls she missed that dad had to prompt her to respond. Also, she had more than a few “why is it doing this” questions that dad helped figure out.
Such a sad tale, poor lady trying to make her flying dream come true (perhaps too prematurely it seems), and whilst doing so her Dad also loses his life as well.
All very tragic, and quite telling that One's Training and your very own aptitude to Fly is paramount.
Poor folks.
All very tragic, and quite telling that One's Training and your very own aptitude to Fly is paramount.
Poor folks.
Seems to me that this autopilot needs to activate the Master Caution if it calls for re-trimming but re-trimming has not been adjusted for, say, 5 seconds.
A little trim up or trim down light on the autopilot itself seems a bit too subtle to me. Is there a trim demand light in front of the pilot as well ?
Of course, any competent pilot would be used to automatically re-trimming after a power or speed change. How did this pilot's lack of trimming and mode confusion come to pass, and why did her instructor sign her off ?
FLY, Navigate, communicate, (capitalisation deliberate).
RIP
A little trim up or trim down light on the autopilot itself seems a bit too subtle to me. Is there a trim demand light in front of the pilot as well ?
Of course, any competent pilot would be used to automatically re-trimming after a power or speed change. How did this pilot's lack of trimming and mode confusion come to pass, and why did her instructor sign her off ?
FLY, Navigate, communicate, (capitalisation deliberate).
RIP
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I took the information about glide slope capability from the operarting manual that someone posted way up in this thread. Of course there are different installations of this autopilot, like with and without pitch trim capability, so not all will be fitted with this option.
Last edited by what next; 21st Dec 2023 at 09:31.
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This is the relevant quote from the manual:
"The Century 2000 may be ordered as a Trim
Prompting autopilot. This means automatic
control (autotrim) of the elevator trim is not
available on these system. When the autopilot
displays a flashing TRIM UP or TRIM DOWN on
the annunciator, the pilot should manually move
the trim control of his aircraft in the direction
indicated on the autopilot. When the autopilot
determines that the trim condition is satisfied,
the trim lamp on the annunciator will extinguish
and the pilot should stop his trim
action. There are 2 degrees of trim prompting. For a small trim error the
trim prompt will flash approximately once each second. A large trim error
will cause the prompt to flash approximately 3 times per second. A large
error not corrected for a period of approximately 2 minutes will sound an
alert for 5 seconds. The alert will repeat every 2 minutes until the large
error is corrected."
Ah, fair enough. I have no specific knowledge of these types or this autopilot, but somehow the out-of-trim condition was missed, hence my questions.
I wonder if the aural alert can always be heard in a noisy cockpit and through headphones, and whether there is a trim light near the pilot's eye line.
Or maybe the pilot got confused and was moving the trim the wrong way - there are some clipped-on notes obscuring the trim wheel,
I wonder if the aural alert can always be heard in a noisy cockpit and through headphones, and whether there is a trim light near the pilot's eye line.
Or maybe the pilot got confused and was moving the trim the wrong way - there are some clipped-on notes obscuring the trim wheel,
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It is in the avionics stack in the middle of the panel and clearly visible for the pilot. Watch this video here (for at long it is still available on YouTube) where she tries out the autopilot after it came back from being repaired:
Everything is possible.