Holding Overshoot

[downscc 1,327]

>>I could fly a hold just using a VOR needleMy instrument currency checks every year (for insurance) always include a holding pattern, which of course gets handflown with VOR only. At least I get to fly with an HSI.I just don't get the jest of this thread. Unless the big iron uses FMS/APFDS capable of flying a track (vs. an inbound course) then any wind will distort the ground track. First, the downwind turn (tail on your tail) blows you the opposite way of the upwind tail and second, the 1-min hold time applies to the inbound leg. The outbound leg will be longer or shorter to compensate and will track left or right on the reciprocal of the inbound course, depending on wind.Do the real 737/747 have boxes that actually fly a defined track regardless of wind??

[Guest Daniel Slade]

>Funny how these birds can follow a LOC or GS signal with>hardly any perceptible deviation, but can't keep on a>racetrack.>>>>PaulCould this not be due to flying in a straight line with the wind only from one direction. When flying a hold you have the wind from everyone of the 360Deg around you.I would question 2 things here, firstly the hold seem rather small, only 1.5 Min, do you really expect an aircraft of this size to turn 2 180deg turns and fly 2 8-10 Nm straight's in this time acuratly. Secondly I would say the speed is too fast for the 20Knot wind, note the aircraft turns perfectly into wind, but fails the turn with a tail wind. My guess would be the only reason it made the first turn was due to the headwind and would have failed the turn without it.Daniel

[downscc 1,327]

>firstly the hold seem rather small, only 1.5 MinThe time refers to the time spent flying the inbound leg only, not including turns and outbound leg. The time spent in the outbound leg is adjusted such that the inbound leg is on target, which is required for any wind situation.The standard hold taught to instrument students is a 1 min leg inbound. Above FL180, I believe the standard to be a 2 min leg inbound but I don't hold much up there in the real world. The only holds that have defined leg lengths are those established on DME fixes; otherwise, it's either 1 min or 2 min.

[Check_Airman 3]

I'm just thinking, it knows how to deal with the meanest crosswinds and gusts during autoland, but not in the pattern. Maybe the AP should be allowed 45 degree banks!!

[jon b 2,047]

Yes, its the inbound leg which is the basis for the timing.I believe its the rate of turn that is increased or decreased depending on any cross winds pressent.When in the BNN hold for example you can see the aircraft above and below you all following the same hold,even though these maybe airbus or boeing all with different FMCs they all seem to do the same thing.I guess with all this automation its why we now have only type specific instrument ratings,IE I can fly a 747-400 in IMC but not allowed to fly a cessna 172 around a hold!regardsJon

[rsrandazzo 6,353]

Gentlemen-It seems that some of the behavior that the main forums are so well known for is bleeding over- so let me put a stop to a few things for those of you who are new here:1) Read the forum guidelines at the top of the forum. 2) Sign your posts with your real name. (see #1 above!)Now- on to reiterate the answer which you already have.I'm type rated in four aircraft- (soon to be 5 if I can find some time free) and not one of the airplanes flies the magenta course in a hold.As Captain Jon pointed out, the magenta track displayed in the hold is symbolic and is based upon a specific hold speed that some engineers at Boeing and Honeywell decided would make a good approximate index for the standard holding pattern in a 747-400.The 747-400 is almost a 20 year old airplane (can you believe that?!) and the microprocessors used in the FMC/FMS are not fast. (That lag-delay in the FMC when you execute the route...processing....slowly.....) Since they are not fast, the engineers elected not to have the system dyanimcally update the magenta track for actual speed. The track is based upon some predicted and pre-determined hard coded variations. The state of these variations will determine what size hold it paints on your ND- but this will only be a close approximation.Now- lets talk a bit about the magenta line: What IS it?If you read the thread above (and ignore the couple of guys who ar just here to tell you how important they are...) you'll notice that there appears to be a common misconception that the airplane is following the magenta line.This is an inverted assumption.The airplane has no knowledge of that pretty magenta line. It can't see it, and it does not follow it.The airplane is following steering guidance that is provided by the FMS in order to follow a pre-programmed route that is defined in the FMS. While flying the route, in order to provide the crew with greater situational awareness, the FMS paints "conformal information" on the navigation display. CONFORMAL meaning that it is correct to bearing and scale relative to the airplane.So- in the case of a track- the megenta line should so closely line up to the airplane's position that it gives the appearance of following the line- when in fact that line is just there to show you what the airplane should be doing. It's iconic.We've discussed with a number of very qualified pilots/instructors and Boeing engineers many aspects of this airplane and "why it does X as opposed to Y." Nobody seemed to have a clear answer on this one- but based on our experience with such things we are assuming it is related to processing power. Since the airplane doesn't have the processing power to dynamically update the holding pattern size- it is not uncommon that the airplane will fly off the race track. If the airplane had the ability to update the track for course/winds/speeds- it would look a bit oblongish and dynamic. In the case of this airplane- it remains as an approximate size/shape icon to depict the location and direction of holding.So- another example of modern technology that works.

[Brian Doney 127]

So to be clear, that would mean, that everyone else who has modelled thier aircraft to hold on the line, even those that have modelled aircraft older than the 744, have all got it wrong ?

[lefteris 70]

Brian-(I am going to still take your question seriously, even though one might mistake it for a whole load of irony)-You have gotten answers from various people with enough credentials inside the 744 to indicate that, yes, they have got it "wrong" in the sense that the real aircraft doesn't hold the magenta line unless the right conditions prevail. What the aircraft flies and what the magenta line shows are two different things: The magenta line is a CALCULATION. Now, if the aircraft veers too MUCH away from calculated airspace, then it might have a certification problem, but please try to understand what others have tried so hard to tell you: The magenta line is a CALCULATION.Best,

[Brian Doney 127]

Lefteris,Thank you for the post.You have gotten answers from various people with enough credentials inside the 744 to indicate that, yes, they have got it "wrong" in the sense that the real aircraft doesn't hold the magenta line unless the right conditions prevail.IMHO Jon's posts are not clear. In one post he says it misses, and in another says it won't. I don't see why it's so bad to ask "Hey PMDG, you guys wanna weigh in here ?" in this case. After all, YOU designed our version of the plane, Jon flies the real one. There is a disconnect there.Again, I do appreciate the reply.

[rsrandazzo 6,353]

Brian-That would depend upon the airplane, I suppose. We didn't model them- so I won't comment on their behavior vs. actual.It is not uncommon for simmers to conclude things about aircraft that are not actual behaviors- it happens all the time. Even with the experience we have in house- we make assumptions based upon our sim experience and sometimes we are wrong and get corrected by the Boeing guys, and/or our Technical Advisors....But as for other people's products? We don't comment- as they aren't our products...

[Brian Doney 127]

Robert,"That would depend upon the airplane, I suppose. We didn't model them- so I won't comment on their behavior vs. actual."Fair enough."It is not uncommon for simmers to conclude things about aircraft that are not actual behaviors- it happens all the time."I completely agree. Also, realize that I made no claims to know one way or the other, I just don't see what is so unreasonable in the OP's request for clarification specifically from you. That is all.Come on now, the OP says:"Maybe somebody from the development team could answer this."in what appears to me to be a very benign tone, no disrespect in the question asked, that I can see.In response, he gets:"No one will answer this because you have not payed any attention to what's already been said, the real world pilot who flys the 747-400 answered your question, if that is not clear enough for you then perhaps carefully re-reading the above posts by jon B will help enlighten all involved, if not then I suggest jumping in a real 747 and check it your self...."Why ? What is up with that ? It's a good question. Why did he deserve that response ?Our personal beef aside, I do not come to here to war with you. Believe that or not, that's up to you. I do think the above exchange is way out of line, on the part of Mr. Smith, and I don't understand why this sort of thing is accepted.

[Guest fcrash]

Robert , my only question is , wicth has not been answer yet , is this.This Holding Overshoot is a problem that only occurs to me , or is this a software problem that everyone has it?PS: I don't really care right now what the real plane does. I wanna know if I have a problem with my software. []s Fernando

[macpac22 0]

Fernandoi tried this myself today and at a speed under 200knots i had a more ACCURATE hold but anything over 200 knots you tend to get more overshoots of the turn , my own feeling is that its down to:1) Weight2) Speed3) Wind (direction and speed)regarding the FMC calculation, you may notice as you set a hold it apprears really small on the ND but as you enter it, the hold spreads out, as in it recalculates your hold as you enter it.just to point out: IT IS NOT A PROBLEM WITH YOUR SOFTWARE!..FACT!!if any of the pilots on here duplicated your hold using the same criteria they would have the same results as your images show, so dont worry :) its normal as stated by Jon. A hold is different to a LOC and G/S intercept basically because you are at different altitudes and also involves turns of considerable bank and it takes time for a 747 to turn and stabilise on a set heading, whereas a LOC intercept and G/S is following a heading with a descent and small corrections...well thats my 2 cents anyways as a SIM pilot loli couldnt believe this topic has grown to 4 pages i guess there is still some bitterness between members on this board, trading insults on a public forum doesnt help anyone! PMDG or customers. I also feel noone has the right to demand an answer from the development team (i personally hate to see that on these forums, not so much of it these days! :) )PaulDublin, Ireland

[rsrandazzo 6,353]

Brian-I'm trying to help you out here- but you are making my point for me. As fast as I can clean this thread, you are adding angry comments that contain personal attacks, venom and all manner of unpleasantness.This is precisely the "ratcheting up" behavior that created all of the confusion when we tried ot help you last time. I would have enjoyed nothing more than to have resolved your previous problem quickly- but this exact behavior made it impossible.Now please- stop.Enjoy the forum, or simply avoid it.

[Guest fcrash]

Hi , I'm having a problem with my holdings , so I will post here some pictures to describe better. As you can see the holding overshoots in a very strange way , and I have done more than 10 holds , all exacly the same overshoot. But on the other side of the hold the aircraft does not overshoot and turns quite perfecly.Any ideas?[]s Fernando