The above graph is taken from the DSTG book “Bayesian Methods in the Search for MH370, ” page 90. It shows the probability distribution of MH370’s endpoint in the southern Indian Ocean based on analysis of the different autopilot modes available to whoever was in charge of the plane during its final six hours. It was published earlier this year and so represents contemporary understanding of these issues. As you can see, the DSTG estimated that the probability that the plane hit the 7th arc north of 34 degrees south longitude is effectively zero.
I interviewed Neil Gordon, lead author of the paper, on August 11. At that time, he told me that experts within the official search had already determined that the BFO values at 0:19 indicated that the plane was in a steep descent, on the order of 15,000 feet per minute.
Such a rate of descent would necessarily indicate that the plane could not have hit the ocean very far from the 7th arc. Nevertheless, Fugro Equator, which was still conducting its broad towfish scan of the search area at the time, spent most of its time searching the area on the inside edge of the search zone in the main area, between 37.5 and 35 degrees south latitude, about 25 nautical miles inside the 7th arc. At no point between the time of our interview and the end of the towfish scan in October did Equator scan anywhere north of 34 degrees south.
Shortly thereafter, the ATSB hosted a meeting of the experts it had consulted in the course of the investigation, and the result of their discussion was published on December 20 of this year as “MH370 – First Principles Review.” This document confirms what Gordon told me, that the group believed that the BFO data meant that the plane had to have been in a steep dive at the time of the final ping. What’s more, the report specified that this implied that the plane could not have flown more than 25 nautical miles from the 7th arc, and indeed most likely impacted the sea within 15 nautical miles.
By the analysis presented above, a conclusion is fairly obvious: the plane must have come to rest somewhere south of 34 degrees south, within 25 nautical miles of the seventh arc. Since this area has already been thoroughly scanned, then the implication is that the plane did not come to rest on the Indian Ocean seabed where the Inmarsat signals indicate it should have.
I would suggest that at this point the search should have been considered completed.
Nevertheless, the “First Principles Review” states on page 15 that the experts’ renewed analysis of the 777 autopilot dynamics indicates that the plane could have crossed the 7th arc “up to 33°S in latitude along the 7th arc.”
Then in the Conclusions section on page 23 the authors describe “a remaining area of high probability between latitudes 32.5°S and 36°S along the 7th arc,” while the accompanying illustration depicts a northern limit at 32.25 degrees south.
In other words, without any explanation, the northern limit of the aircraft’s possible impact point has moved from 34 degrees south in the Bayesian Methods paper in early 2016 to 33 degrees south on page 15 in the “First Principles Review” released at the end of the year. Then eight pages later within the same report the northern limit has moved, again without explanation, a half a degree further north. And half a page later it has moved a quarter of a degree further still.
Is the ATSB sincere in moving the northern limit in this way? If so, I wonder why they did not further search out this area when they had the chance, instead of continuing to scan an area that they apparently had already concluded the plane could not plausibly have reached.
I should point out at this point that the area between 34 south and 35.5 south has been scanned to a total widtch of 37 nautical miles, and the area between 32.5 and 34 has been searched to a total width 23 nautical miles. Thus even if the ATSB’s new northern limits are correct, they still should have found the plane.
As a result of the above I would suggest that:
a) Even though most recent report describes “the need to search an additional area representing approximately 25,000 km²,” the conduct of the ATSB’s search does not suggest that they earnestly believe that the plane could lie in this area. If they did, they could have searched out the highest-probability portions of this area with the time and resources at their disposal. Indeed, they could be searching it right now, as I write this. Obviously they are not.
b) The ATSB knew, in issuing the report, that Malaysia and China would not agree to search the newly suggested area, because it fails to meet the agreed-upon criteria for an extension (“credible new information… that can be used to identify the specific location of the aircraft”). Thus mooting this area would allow them to claim that there remained areas of significant probability that they had been forced to leave unsearched. This, in effect, would allow them to claim that their analysis had been correct but that they had fallen victim to bad luck.
c) The ATSB’s sophisticated mathematical analysis of the Inmarsat data, combined with debris drift analysis and other factors, allowed them to define an area of the southern Indian Ocean in which the plane could plausibly have come to rest. A long, exhaustive and expensive search has determined that it is not there.
d) The ATSB did not fall victim to bad luck. On the contrary, they have demonstrated with great robustness that the Inmarsat data is not compatible with the physical facts of the case.
e) Something is wrong with the Inmarsat data.
@Hank
Generally, effectively “cutting losses” means taking an ego out of play. Sticking with something not producing anticipated results will rarely work, but the alternative of failure can be paralyzing.
It would be tragic for the investigation if it was affected by ego but given the unprecedented circumstances of MH370 it is entirely possible.
Without the expertise of comparison, it is necessary to remain humbled by the challenges, and accept error as a tool rather than an embarrassment.
@Matt M
“In the meantime, do we all agree that constant true tracks (other than the cardinal points) over great distances all end up in one pole or another?”
Yes.
Moreover from Wiki below:
begin cut-paste//
All loxodromes spiral from one pole to the other. Near the poles, they are close to being logarithmic spirals (on a stereographic projection they are exactly, see below), so they wind round each pole an infinite number of times but reach the pole in a finite distance. The pole-to-pole length of a loxodrome is (assuming a perfect sphere) the length of the meridian divided by the cosine of the bearing away from true north.
end cut-paste//
I really did not need the part below today. I have reached my quota of suffering for the day, and I am very close to my 10,000th step of half the distance remaining to the wall.
so they wind round each pole an infinite number of times but reach the pole in a finite distance.
@Matt Moriarty,
“the aircraft maintains its existing track” and the no Track Hold comment.
That is exactly my point. There is no contradiction if you view the manual as information for operational pilots in an operational sense. The aircraft . . .maintains its exiting track [for a relatively short period of time, consistent with normal operational requirements]. The manual does not say it is TRK HLD, which by definition would compensate for changes in the wind field nor does it say that the track is held for hours afterwards.
@Matt M & @Brian A and @DennisW:
I just completed the experiment which did not take as long as I thought it might. I set up two waypoints on the same latitude 1 degree (longitude) apart. This set me on a 90 deg track. I applied a crosswind of 18 kt and flew at FL350 and M0.84. I then overflew the second waypoint while in LNAV mode.
Under this condition, the only way the true track would remain at 90 deg is if the navigation mode was true track. If flying a heading, wind would change the indicated track. If flying a magnetic heading or track, the magnetic variation would change the true track indication. If flying a great circle, then the path would not remain on a latitude.
After flying thousands of miles, the true track indication stayed at 90 deg. Therefore, I conclude that in the FSX/PMDG777 model, the plane flies a true track after reaching an End of Route.
Now whether or not this applies to a real B777 is the question.
@VictorI
Now I am a bit confused. Unless the latitude was at the equator the great circle track would not be at 90 degrees.
What latitude did you use? For example, at 50N (one degree of longitude separation) the initial bearing is 89 22′ and the final bearing is 90 38′.
@all
I would like to ask a question re the 1825 re log on.
We all know it was done by AES without the usual AES ID number as per Fact.Information.
My questions:
How did it work for the AES to know the right satellite and GES and frequency, if the own identity is not known;
for the satellite to do the right thing ( forwarding to the right groundstation)
and for the ground station ? Would the GES store this or would it fail, since without the ID it has no basket number?
If we look at the excellent paper from Paul Sladen (http://www.paul.sladen.org/download/aaib/sladen-20140703-briefing-note.pdf) … we see, 19 out of 28 columns were not published – “for better readability”.
Why would the redacted publication contain GES and satellite ID, but not the AES ID and DP AES owner?
Is it even possible, the Dickinson/Sladen piece refers to the payload data log, and Inmarsat has more data than the customers like MAS do pay for?
Thank You.
@VictorI @others
First I really enjoy this discussion I like to say. The level it’s on is both stimulating and educating (to me at least).
So as a non-pilot or expert I won’t intervene with posts on the matter unless I have something I really don’t understand and question. Don’t let it distract you but if it makes any sence to the topic of discussion I hope you want to explain:
You suggest that after an end-of-flight/route discontinuity the plane flies a true ‘track’. You than mean a magnetic track which is compensated for wind variations but not for magnetic variations?
And to fly a ‘track’ isn’t it necessary to have another ‘trackpoint/waypoint’ to fly to?
I understand (from the discussion) after an end-of-flight overflying the latest entered waypoint there is no other waypoint to fly to. The FMC just takes a snapshot of the latest heading and the plane flies on on that magnetic (true?) heading.
I assume when there is no other waypoint chosen by the FMC after end-of-flight there cann’t be a ‘track’ only a magnetic (true?) heading following the latest saved ‘snapshot’ heading.
Makes this any sence?
@GeRijn
A track after overflight is not only possible, it’s been proven to be the case at end-of-route. Everything in LNAV is wind corrected because everything in LNAV pertains to a course over ground.
The only question which remains – especially as it may pertain to MH370 – is whether that is a MAG TRK as shown in the ND or a great circle route (or, as Victor asserts, a true track).
@Matt Moriarty
Thank you.
Can I then conclude from above that after an end-of-flight/route discontinuity, which was flow untill that latest (overflow) waypoint in LNAV, the mode changes to MAG TRK or true track in which wind variations are corrected also but not magnetic variations?
I probably should add; when there is no further pilot input just before or after the end-of-flight/route discontinuity.
@victorl. May I suggest another quick experiment to settle the issue wrt your flight sim program on true vs magnetic? Choosing a part of the earth where magnetic variation changes quite rapidly, could you start at 30S, 30E, fly to 31S 31E, zero wind field, allow route discontinuity to occur, and then see what happens next?
@DennisW: Good point, Dennis. The indication was 90 deg track. Whether it was slightly off that, I don’t know. Wind, magnetic variation, or great circle paths would have caused a much greater variation in the true track than 1 deg. I could re-run the experiment and see if the latitude was slowly changing along the path. I suspect it was.
@Paul Smithson
I would suggest to introduce a rather strong wind field in your experiment request too?
Otherwise I assume the difference between true and magnetic could be very small or zero without wind, assuming the possibility magnetic track is not compensated for wind variations (which is still not quite clear to me..).
But if it’s your goal only to find out the difference between a true and magnetic track along the latitudes you suggest I can see the value of such an experiment only regarding to this circumstances.
I’m in writing-mode so I’ll explain my simple analogy.
When I plotted a course on a sailing trip I had mainly 4 values to deal with: Magnetic North, True North, my trip-end-destination point (end waypoint..) and the wind. I’ll leave water-current out for simplicity.
My course toward my end-point makes my track.
In Holland if I’m sailing ~North I’ll compensate for magnetic North to true North with ~3 degrees off from magnetic North Pole (heading towards the East).
Lets say a strong wind is coming from the West (which is almost always the case in Holland..) and my end of trip destination is 30degrees north/east from true North.
I have to compensate 3 degrees on track for magnetic North and maybe 10 degrees for wind to reach my destination.
This would mean I have to put my ‘heading’ at least 13 degrees under the magnetic pole direction to reach my destination at 30degrees.
So I have to sail a ‘heading’ of at least 17 degrees to reach my destination at 30 degrees.
This can only be done when compensating for wind and magnetic North Pole versus true North Pole.
If I ‘oversail’ my target-destination and with that haven’t got another target-destination anymore I’ll sail on, on my plotted course (effectively a great circle route I suppose).
But still the question ofcourse is; makes the FMC/autopilot same decisions.
Correction; ‘~3 degrees off from magnetic North Pole (heading towards the East).
Should be; ‘heading towards the West’
I seem to have a basic problem with East and West confusing eachother.. no intend whatsoever
There was enough crosswind to produce a 2 deg difference between track and heading. The track was maintained at (close to) 90 deg true. I purposely selected wind and a path such that the wind and magnetic variation would have produced a detectable change in the 90 deg track.
I am going to re-run the experiment to verify that the latitude is slowly changing due to the small deviation from 90 deg that @DennisW correctly discusses. I was at 37N latitude, where a great circle path between two points 1 deg apart would start with a track of 89.7 deg and end at 90.3 deg. The display with a 1 deg resolution would show a constant 90 deg after the last waypoint even if really at 90.3 deg. However, I can determine the exact track by creating flight files and examining the velocity components in the world coordinates, or by determining whether the latitude is slowly changing due to the 0.3 deg deviation.
I am also going to change the wind along the way to be sure that the track is maintained under changing conditions. This would ensure that a constant true heading with constant wind isn’t masquerading as constant true track. After a change in wind, I’ll see verify that the track remains the same.
@Ge Rijn asked, “You suggest that after an end-of-flight/route discontinuity the plane flies a true ‘track’. You than mean a magnetic track which is compensated for wind variations but not for magnetic variations?”
You have to remember that in a B777, like other modern aircraft, the direction is determined by gyros and GPS, not a magnetic compass, and therefore needs no compensation for magnetic variation. The magnetic variation is added for display purposes or for navigation if flying with constant magnetic heading or magnetic track.
@VictorI @others
But then in my view you (and others) give no conclusive answer to my questions.
But the experiments you are preparing to perform probably will..(?)
The gyros and GPS (if all functional) would then let have saved the FMC a final snapshot of their coördinates and direction at route discontinuity. To fly on on the same track and course (great circle route).
But if their was no continueing waypoint (to McMurdo f.i.) where would a next destination fly to?
If the FMC/AP had no next waypoint (McMurdo?) in his memory what would it do after a route discontinuity? Isn’t a great route impossible then?
For me that’s the basic question in this matter.
@Ge Rijn: As @DennisW as pointed out, an initial position and initial track define a great circle route. I presented this above as a differential equation that relates change in track to latitude and change in longitude. Theoretically, you don’t need to define the next waypoint to stay on a great circle path as long as you know your current track.
@VictorI
A quick “back of the cigarette packet” calculation suggests that a constant magnetic track (ie, compensating for sidewinds) constant airspeed M0.79, from ISBIX, initial bearing 186.23, could possibly arrive at the 7th arc at about S35.5, E92.25 at the required time, while maintaining M0.79, at FL350, with groundspeed affected by headwind/tailwind and speed of sound variations with temperature as flight progresses south.
I completed running a new experiment and got a surprising result. The track did indeed change with wind. The reason I did not see this before was because I kept the wind field constant, so whatever wind corrected heading that existed at the EOR was maintained. Since the wind field was constant, the track was also constant. By changing the wind after the EOR, I observed that the track changed but the heading remained almost constant.
So, I now conclude that after reaching a route discontinuity in LNAV mode, the path continues on a constant true heading on the FSX/PMDG 777-200 ER.
If this is behavior is representative of 9M-MRO, to reconstruct paths which include an EOR, you would need to know the heading at the EOR (which will in general be different than the track at that point) and the wind field along the route. That’s unfortunate because any heading variation at the EOR due to a local variation in wind will propagate for the rest of the path.
On the other hand, I believe that MH370 was flying to a distant waypoint at the time that the fuel exhausted. If correct, the wind doesn’t matter very much in defining the terminus.
@VictorI
My suggested test is a variation of your McMurdo route, APASI (near VOCX) to YPCC (Cocos) should proceed very close to NOBEY if on a great circle.
One thing I am worried about is that the 16x FS9 speed up rate does change some results, so I was planning to do some 1x versus 16x tests, for example using your 180S mag paper as a calibration. I have loaded 2017 mag headings table into FS9, not seeing 2014 readily available.
I am curious if we know what users mods that Z might have made to FS9, like stars and mag headings. I don’t think I know if the Z FS9 was an older version that Z had made a lot of user tweaks, or just an on-the-fly re-install due to reportedly his FSX not working.
(I have both FSX Steam version and FS9 installed, but so far I only do Cesnas around my house and Wash DC on FSX).
@TBill: I have no idea whether ZS updated the navigation database and the magnetic variation data.
@Rob: As I said, after an EOR, LNAV is displayed in the PFD, MAG TRK is annunciated in the MFD, but the plane holds a constant true heading. The value of magnetic track shown in the MFD changes with changes in wind and changes in magnetic variation. In the special case that the wind field is non-zero but constant, both the true heading and true track are constant.
@all
when numbers lead to nowhere
Our brilliant minds and formidable experts seem to have missed the point, when Jeff Wise proposed the summary of the last three years into the division of spoofs and nospoofs. He didnt say that, but i think he fels that the nospoofs started on a very extremely bizarre and therefore extremely weak assumption of a pilot suicide.
The underlying assumption of the search in the SIO was unquestionable the thesis of a pilot suicide. Here, mere technicians and IT nerds decided, that there was a HIGH PROBABILTY of a pilot suicide. They forgot to mention, that they are not even on an amateur level in psychological analysis. This in oposition to the judgement of the indeed exsperts in pfofiling and psychology who laid down in the FI, that there was not the slightest hint to any such scenario.
Now esteemed professional Scientists like Victor or others risk all there scientific reputation by continuing their foolish looking psychological misjudgement. They are pretending to be experts on the psychological what they obviously are not.
So, when a number crunching leads to a extreme bizarre murder and suicide assumption in opposition to all Expertise on the field of the science of Psych9ologiy or profiling, we wshould ask, is there a bug in the numbers or is the science of psychology entirely wrong and has to be rebuilt?
@VictorI
It seems we’ve come to a consensus on this for now?
After flying in LNAV to a waypoint without any input of a pilot before or after, the flight mode changes to magnetic true heading (not track).
The flight path after end-of-flight/route discontinuity is both subjected to changes in wind and magnetic variations as you explain to @ROB as I understand you well.
IMO this is very important information.
And a bit of sad for it leaves a lot more possible flight paths if wind variations were not compensated by FMC/AP after a route discontinuity.
IMO true magnetic heading would mean compensated for wind variations. But this is not the case I understand from you.
Leaving multiple other magnetic routes open.
@Cosmic
Psychology is not a science. It is a subject area.
@Ge Rijn: A direction is either referred to as magnetic or true, not both.
I’m saying that in the FSX/PMDG777 model, after an End of Route (EOR) condition in LNAV, the plane continues to fly on a path of constant true heading. The path as defined by geodetic coordinates is therefore affected by wind. It is not affected by magnetic variation. However, the value of MAG TRK shown in the MFD will change with wind and magnetic variation, while the true heading remains constant.
@CosmicAcademy: I am not worried at all about my scientific reputation. In fact, I even post using my real name. Many here don’t.
The wind needs to change to distinguish heading hold and track hold. If constant wind vector you can’t distinguish the two. So my suggestion is to do as above (for definitive answer to the M / T issue. Then repeat same waypoints route with a variety of wind conditions.
@Paul Smithson: If you read my earlier post, I said that in my more recent experiment I changed the wind along the path. The true track changed, the true heading did not. I am quite confident in the result that the aircraft follows a path of constant true heading after an EOR. The only question in my mind is how well the FSX/PMDG777 replicates the behavior of a real B777. That will be hard to answer.
@Dennis
Sure i am in your camp, since i i see that the spoof ideas are in a quite a premature state, but also the Inmarsat and SIM data lead to extremely bizarre and complicate scenarios, that are nowhere supported by anything than the pure fantasy of the search leaders.
The first science of humanity was the science to survive and in times of cannibalism there was no choice as to be perfect in instant psychological analysis, because you never knew whether the person you meet, was the person to eat for latenight dinner. What i want to say is, that psychology is a very ancient subject ebven it is a subject area.
@Victor
You said here yesterday, that you see a high probability for a pilot suicide and you just dont have the credentials to do that. You may have a private opinion, but you are publishing here as a scientist of some standing. The public and the world wide readership think that you are saying that private opinion as a kind of research you did. May your figures lead you to the conclusion, but as long as the experts on that field dont corroborate your conclusion your figures and numbers end nowhere, or at the southpole right now.
The Inmarsat data is a very small database, and since the locating of a plane is done for the very first time, there is no experience at all, how to way the different problems with the data as laid out by Dennisw (eror margin of BFO) or the vast diferences to the test flights. If you enter a comletely uncharted area, you canot even tell whether you came anywhere near to a solving.
BTW if you click on my nick you find my website with extensive biographical data, fon-numbers and else. nothing to hide like you. My nick on reddit was WHATMAKESREALLYSENSE, because i never gave much on the idea, that a Beijing bound plane will be found 10.000 kilometres away in the opposite direction. If a pole i would rather opt for the north pole than for McMurdo
@VictorI
So, as I understand it, when the plane reaches an EOR, the autopilot reverts to constant true heading, which is not affected by changing magnetic variation as the flight proceeds, but is affected by changes in the wind field.
@Ge Rijn
Here is my sum up, somebody correct me if wrong.
Victor is saying what most expert folks seems to say: (1) first of all, somewhat hard to believe, nobody aside from Boeing and maybe Honeywell really knows the answer to how a real 777 behaves at end of waypoint (discontinuity), but (2) most experts believe it is true track heading, and that is what the most sophisicated PMDG flight sim model seems to show.
MattM is saying from his sim work, he thinks a real 777 might continue on a great circle route after the last waypoint.
Here is my artist rendering, someone else may do better at this. Black line is approx. true track whereas purple is great circle. Magnetic heading would be in between these extremes (closer to True Track) but with very severe wind or closer to poles could curve towards the Great Circle path.
https://docs.google.com/document/d/1jIaz5ByqQXiGR3nIxPbqd0Fm14wbUmMTdzb1_uyHnIk/edit?usp=sharing
Thanks for sharing @Victori. Two supplementation, if I may. 1) are we sure that the heading info displayed (represented as M but which you believe to be true, i.e. unaffected by changes in local mag declination) is the actual ground track and not the aircraft’s head? Or indeed, vice versa. 2) if experiment does not include a path where declination changes by >0.5 degree, how can we be sure it’s T not M?
*supplementaries, autocorrect…
@TBill said, “most experts believe it is true track heading, and that is what the most sophisicated PMDG flight sim model seems to show.”
“True heading”, not “true track heading”. It can’t be on the same track and heading unless there is no crosswind.
As for what experts believe, I don’t know. Continuing on LNAV after a discontinuity for thousands of miles would not be something a pilot would ever do, so there is a lot of disagreement as to what would occur. So unless Honeywell chimes in with a more definitive answer (unlikely) or supplies the source code (even better but much less likely), it will be difficult to resolve this.
@VictorI
OK yes correction True Heading which could be impacted by wind. My artist rendering is the no wind case.
This is all so confusing…
@Paul Smithson said:
“1) are we sure that the heading info displayed (represented as M but which you believe to be true, i.e. unaffected by changes in local mag declination) is the actual ground track and not the aircraft’s head?”
First, I didn’t say the display was incorrect. It correctly displays the magnetic track (or the true track if the HDG REF switch selects TRUE instead of NORM). But the value displayed is not constant. It varies with wind and magnetic variation.
At various times along the path, I checked four values: true track, true heading, magnetic track, and magnetic heading. Only the true heading was constant.
“2) if experiment does not include a path where declination changes by >0.5 degree, how can we be sure it’s T not M?”
I checked this over long distances where magnetic variation changed by several degrees. The true heading remained constant.
@Cosmic Academy: Yes, my opinion is this was a case of pilot suicide. I stated this on a blog, not in a refereed journal on psychology. I could state why I believe that things going on his personal life were consistent with somebody that was depressed, but that would lead to pointless arguments here.
For those of you that wish that believe it is impossible that the pilot was the culprit, you need to explain the extraordinary existence of a simulated flight from the Andamans to a point of fuel exhaustion in the SIO. A simulation that was created in the weeks before the disappearance of the plane.
Arguments such as there is no proof the points are from the same flight, the plane in the simulator could not have been flown in a way to produce those points, and the simulator was broken, have all been proven false. So either the pilot was the culprit, or he is being framed, or this is all some extraordinary coincidence. There are no other options. My opinion is the pilot was the culprit. I would rank him being framed as the second possibility.
Relative to your comments about the Inmarsat data, I have no idea what your point is.
@Victor et al,
I think that Victor deserves a medal. After years of speculation and debate he has shown precisely what I believe the manuals to say, and the response from my Honeywell contact to say.
We have to be very careful with the interpretation of the words and the definitions to make the answer perfectly clear.
We also need to understand that the aircraft determines it’s position using INS and GPS systems, and does all the navigation calculations with reference to True north. It is only when the calculations are complete that the software does a look-up to convert True heading to Mag heading in order to display the appropriate [pilot selection] number on the MFD.
While it is possible, mathematically, to calculate a continuation of a current track, based on knowledge of the current heading, wind and magnetic deviation that does not mean that the aircraft FMC is able to do so. There is no requirement in an operational sense to do so, so why would the additional software and computational complications be implemented. The Honeywell response to my question says that there is no TRK HLD method implemented with this type of scenario.
There is an interesting corollary to all this. Why did the ATSB come to the conclusion that Constant True Track was a potential end of flight mode?
@Brian Anderson: Can we line up all the statements from Honeywell and manuals? It would take some work for me to find them all. I suspect you have them at your fingertips.
As for why the ATSB considered CTT, it might be that the ATSB considered the pilot selecting this mode, which would require changing the HDG REF from NORM to TRUE and the mode switch for heading from HDG to TRK. But as you say, if there was no pilot input, a route discontinuity would not cause the plane to fly on a CTT path (assuming we can trust the PMDG model).
@Brian
Good question posed by you:
“Why did the ATSB come to the conclusion that Constant True Track was a potential end of flight mode?” and I would want to know that you are suggesting the correct answer is “True Heading (with wind impacts)” vs. a “True Track”.
I am thinking Victor’s paper June_2016 paper below shows both the wind and no-wind paths on the 180 South magnetic heading on 8-March-2014, and wind impact is significant but not huge.
http://www.duncansteel.com/archives/date/2016/06
I greatly appreciate you and Victor and the others giving us your knowledge and perspectives. Qualitatively I am in general agreement with Victor on MH370.
That’s perfectly clear now. Many thanks, Victor
@Victor,
I have only the one statement from Honeywell.
Phew ! all the other references ? No, I don’t have them at my fingertips and they are not necessarily precise little descriptions. Rather they are snippets of information that, in total, create a picture that still might require some interpretation, and certainly require to be read with the mind of an operational pilot. I did include some in the discussion paper I wrote on the draft DSTG book that was published on Duncan’s website. Unfortunately I can’t find that link now.
@Brian Anderson: Here is one from the FCOM, under the section “FMC Alerting Messages” in Chap 11:
***END OF ROUTE: LNAV active and end of active route overflown. AFDS maintains last heading.***
So, the implication is the AFDS maintains the last heading and there is no correction in heading for changes in magnetic variation, i.e., a true heading path is flown.
To complicate matters, it may be that route discontinuities are handled differently than end of route conditions.
@Victor:
You said: “So, I now conclude that after reaching a route discontinuity in LNAV mode, the path continues on a constant true heading on the FSX/PMDG 777-200 ER.”
Nice work. It’s good to get a definitive result, although it does not prove, as you also said, that a real B777 behaves the same way. I suspect it does. That result is not an obvious choice, and I suspect it is copied from the real software function. I have (again) asked that question of ATSB, this time via a new conduit. I’ll let you know if I ever get an answer from ATSB.
As I have been saying for some time, there does not appear to be any constant magnetic heading route that matches the satellite data.
There also does not appear to be any magnetic track route that fits having only a single southward turn. I have constructed one that does fit, but it needs a turn SSW before 18:40 and a second turn S some time later after 18:40. I don’t think it is a good candidate.
It is also possible to construct a great circle route that fits, as you have done, but it involves a lengthy loiter and terminates far to the NE.
There is one constant true heading route (to ~35S) that fits, and it has a southward turn before 18:40 and an EOR at ANOKO. An interesting new result is that its speed matches the optimum Holding speed at ANOKO at the same altitude as the military radar track to 18:22. Maybe there was no altitude change at all after ~17:30? It appears that it may be possible to fit a CTH route from ANOKO at a constant KIAS. I say “may” because the wind errors in my current, somewhat simplified, wind model are a bit large. This discrepancy may go away when I implement a full 4-D wind model and integrate it along the route. In this case the constant KIAS set at FMT would be used instead of the variable Holding speed profile I first suggested. So far I am agreeing with you that this mode does not seem to be available in the FMC. I have also asked ATSB about this issue.
VictorI
“All very confusing”
I would echo that, little wonder the AUSSiES are confused, as well 🙁
@Brian Anderson: I just completed a new experiment to determine what happens at a route discontinuity. (There is a distinction in terminology when you pass the last waypoint versus when you pass a waypoint that is not connected by a leg in the route to the next waypoint.)
The answer is, according to the PMDG model, the two conditions behave the same way, i.e., the true heading is maintained.
@DrBobbyUlich: Yes, that’s all interesting.
As for holding speed, you are safe to assume that there is no way to automatically maintain holding speed using the autothrottle. For instance, this reference describes how to find the Best Holding Speed, which can then be manually input for the SPD mode (not described). It describes a very similar procedure to what I described.
http://www.flight.org/how-slow-can-you-go
Quote from VictorI: “So, I now conclude that after reaching a route discontinuity in LNAV mode, the path continues on a constant true heading on the FSX/PMDG 777-200 ER.”
Hello VictorI. Here’s an experiment for you. Program in a diversion to Banda Aceh via Vampi, Mekar, Nilam, Sanob, BAC at FL350 (35000 feet) and Mach 0.84 (the standard cruise speed for the B777), but with the Left IDG and Backup Converter both inoperative (very important). Transfer 850 kg of fuel to the Left tank from the right. Now just let it fly.
Notice at Top of Descent (15 NM prior to Mekar) the aircraft slows to VNAV descent speed of 272 Knots IAS (~473 knots True Airspeed). Notice around 1825 UTC at 3 NM prior to Nilam, the Right HGA is finally exposed to the satellite during the left turn. Coincidence that the Satcom logs On? Then around 40 NM prior to Banda Aceh the aircraft slows to 240 KIAS. Over Banda Aceh it maintains LNAV but actually reverts to flying a constant Heading in degrees True. Then at 40 NM south of Banda Aceh it accelerates back to 272 KIAS. Then notice how it passes over very close to each arc (you will need to enter actual winds) and ends up at the ATSB hotspot but with 850 kg of fuel still onboard at 0017:30. You will probably have GE90-110B1 engines so you will have to manually shut down the right engine to simulate fuel starvation. Notice the left engine is still operating but all electrical power is lost (left IDG and backup converter failed at start of experiment, and right IDG now fails due to right engine fuel starvation). The APU should start using fuel from left tank. Electrical power is restored, load shedding occurs (no IFE) and the speed window defaults to 200 knots. The autothrottle then adjusts power to maintain 200 KIAS and dampens out the phugoid motion. Due to flight envelope protection and TAC the aircraft ends in a fairly stable condition. The left engine fails around 0027 UTC and the aircraft ends in a glide. Now it hits the water, possibly with right wing low (hence only right wing debris found) at about 90 NM from the seventh arc. RIP MH370.
Of course this scenario requires the satellite log on data to be abnormal. Which is possible, if the EE Bay was damaged from an oxygen bottle rupture next to the Left AIMS Cabinet. The bottle that was serviced by Malaysia immediately prior to take off.
Oxy