Jimm

Overshooting Flight Plan Path

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Sort of an odd question, but one I have been fighting here recently.

 

So I still follow the tutorial distributed by PMDG.  Yes, I still have yet to master the FMC, but I'm learning more and more as I fly.  With respect to the B737-NGX, I noticed last night while flying the Tutorial #1 flight, that my aircraft fails to stay on it's flightpath.  I have both LNAV and VNAV active (with autopilot set), but as it approaches turns ion the path, it appears to overcompensate and as a result, when it approaches a straight vector, the plan has to do three or so slight turns to correct the flight vector in relation to the plan vector.

 

With that said, I have come across a few variances between what is in the tutorial and what I get as results in the FMC.  The biggest difference are waypoints, but Kyle mentioned to me before that is due to AIRAC cycles, so I try to take that with a grain of salt, but somehow I feel that with those variances, it is messing with the way the aircraft follows the path.  My V speeds tend to be more than what is in the tutorial, about +5knts.  Trim settings are more as well (those together cause me to have to take more time down the runway).

 

What I really want to know is whether or not it is normal for the NGX to overshoot or overcompensate the flight plan path and what I am witnessing is normal?  I tend to believe I may be doing something wrong, I just don't know what it is.  As for the other issues, maybe it's the same thing.  I will admit fault if it is my fault, I just want to learn this aircraft and learn i correctly.  No offense to PMDG, but if they had made any improvements, or if cycles had changed, that they could at least update the tutorial to help out those who are just getting into the NGX now and with the variances coming up, it can be confusing.

 

-Jim

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Normal, if you are referring to the lateral path, it does not blindly follow the magenta line.  Those lines and arcs are predictions only, the AFCS will command turns based on the navigation modes.  This opens the door to the pilot becoming more pilot than observer.  It is not unusual for me to manipulate the next waypoint to take the kinks out, for example just selecting the next waypoint on top of itself will "reset" the predicted path and often make for less overcompensation..

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Ok, then let me ask this, would speed affect the aircraft shooting for the path?  I do know that prior to takeoff, my vspeeds were a lot more than what the tutorial stated.  Assuming that would be the case, then why wouldn't the FMC know, based on the data provided, that a waypoint was approaching and could compensate in time?

 

-Jim

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Speed affects the path and so does the waypoint type.  The FMC can compensate, up to a point, for 'fly by' waypoints but must overfly 'fly over' types.  If the 'fly over' waypoint has a sharp turn, the aircraft will overshoot according to speed and weight.

 

David Jones

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Speed affects the path and so does the waypoint type.  The FMC can compensate, up to a point, for 'fly by' waypoints but must overfly 'fly over' types.  If the 'fly over' waypoint has a sharp turn, the aircraft will overshoot according to speed and weight.

 

David Jones

Oook, now I understand.  Thank you for the clarification.  Maybe I just didn't notice the behavior before until now, that's why I thought it strange and assumed something was wrong.

 

Thanks again.

 

-Jim

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 Hi Jim,do you fly IFR?   I'm sure you'll  enjoy it even more especially when atc gives you the approach and you catch the localizer.   That's just about the nicest thing in FS for me.

 

Cheers

 

john

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 Hi Jim,do you fly IFR?   I'm sure you'll  enjoy it even more especially when atc gives you the approach and you catch the localizer.   That's just about the nicest thing in FS for me.

 

Cheers

 

john

Right now, I am avoiding anyone or anything telling me what to do when I fly.

 

Ok, that didn't come out right.

 

I don't use any type of ATC when I fly as I am still learning the intricacies of using the FMC.  My OP was dealing with the PMDG tutorial, so that should give you an idea of my experience. lol :lol: 

 

Maybe one day, when I get really good at it, I'll try my hand at ATC.  Thanks anyways.

 

-Jim 

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Maybe one day, when I get really good at it, I'll try my hand at ATC.

 

Honestly, I find it a lot easier when I have (human) ATC. Then again, that's also because I know how most of the flying should be, so when I procedures that are usually dictated by ATC, I'm anticipating giving myself vectors during that portion, which can increase my workload. The same goes for runways. Sometimes, ATC will not assign a runway at a particular facility (ROA's 34 is aimed at a mountain, as an example, so they will not assign departures to it). If it were coming from some other person, then I'd only be responding to the instruction instead of continuously evaluating a "vector plan" of sorts in an area I'm unfamiliar with, or look at FlightAware, or VATSIM's various group SOPs for controlling to get a better feel for how it would truly go. East coast? I'm okay. Anywhere else? Not so much.

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Honestly, I find it a lot easier when I have (human) ATC. Then again, that's also because I know how most of the flying should be, so when I procedures that are usually dictated by ATC, I'm anticipating giving myself vectors during that portion, which can increase my workload. The same goes for runways. Sometimes, ATC will not assign a runway at a particular facility (ROA's 34 is aimed at a mountain, as an example, so they will not assign departures to it). If it were coming from some other person, then I'd only be responding to the instruction instead of continuously evaluating a "vector plan" of sorts in an area I'm unfamiliar with, or look at FlightAware, or VATSIM's various group SOPs for controlling to get a better feel for how it would truly go. East coast? I'm okay. Anywhere else? Not so much.

One regret I always had was taking the opportunity and time to be closer to aircraft.  I missed the boat a long time ago, but I'm trying to make up for it by taking it up as a hobby.  I've made the comment several times before that I am wanting to really learn how to fly jets like the airline pilots do, and I know ATC is another step, just not there yet.  I have to first get comfortable with flow - meaning that from startup to shutdown and everything in between.  I'm not ready to embarrass myself to another human yet. lol

 

I have a certain amount of envy for those who feel that flight sim is second nature to them, most likely because they fly in real life with a close second to those who use flight sim everyday.  I try to make time for it, but with a sick wife, long hours at work, and trying to maintain an exercise regimen, I don't have the time available to do some deep training, so I whittle away as best I can.

 

Thanks for the tips guys, it is appreciated.

 

-Jim

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Honestly, I find it a lot easier when I have (human) ATC.

 

Fully agreed! One of my favourite approach (on a big airport) is the parkway visual 13L at KJFK. However, there is quite of a portion of radar vectoring to link between the end of the STARs and the final approach especially when turning around KJFK by the North then overseas. When vectoring myself, I find it difficult to get close to a CDA. I usually end up reaching 3000ft too early (or sometimes have to raise the speed brakes fully up...).

 

With a Human ATC to manage the vectors and the descent, it gets way easier.

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I'm not ready to embarrass myself to another human yet.

 

You'd be surprised. When I'm online as a controller, I usually take the stance that nobody is going to be able to do what I want them to do until proven otherwise. In the past few years, it's gotten so bad that I rarely even give directs anymore because people don't understand what I'm asking (seriously - and I've been controlling less often because of that downtrend). If someone shows an inkling that they even care, that's a huge step in the right direction, and I'll usually start giving them "normal" (realistic/advanced) instructions. It's less that people screw up. It's more that people don't realize how badly they screw up and don't care. I'd prefer to have someone who's worried about messing up, because that usually means if I tell them how not to screw up in the future, it isn't a wasted effort. I have a feeling that you'd enjoy the whole thing a lot more by taking the leap of faith.

 

Honestly, everything starts falling into place when you start flying with online ATC, knowledge-wise, as long as you're paying attention. So many of the concepts of IFR flight are directly related to ATC, traffic flows, sequencing and loss of comms. A lot of those functions are there in the FMC and on the MCP to help the crew manage things, but without exposure to the source of why they're there in the first place, you have to grasp at abstracted concepts instead of understanding how they fit into the larger picture. You can see it here all the time:

  • ...when people ask when to use the other autopilot modes other than LNAV/VNAV. If you'd never gotten a vector, then you probably wouldn't fully understand the reason for HDG SEL. If you never had to dump off of LNAV into HDG SEL and noticed a slow descent because you're still in VNAV, then you'd never fully understand the reason for FL CH or V/S (though V/S is usually first somewhat experienced through the default MS planes).
  • ...when people seem utterly lost when they see a discontinuity in their route, and will stop at nothing to "resolve" it, even though it's supposed to be there because that's where ATC will vector them, and in many cases is best left in there.
  • ...when people want to set the approach and runway into the FMC for an airport over 6 hours away, because they don't see how ATC constantly evaluates the weather picture to properly select a runway and may change the runway multiple times in those 6 hours.
  • ...when people think that entering the wind in the FMC perfectly is there simply to give them a better prediction of when they'll arrive, and with how much fuel, instead of thinking about non-radar procedures, where you're asked to give a standard position report with predictions (which is also why the PROG > POS REPORT page looks the way it does on equipped FMCs).

The interesting thing about knowledge is that it is better obtained and solidified through real world application (Thorndike Law of Exercise). Learning how to set up the FMC is one thing, but when one sees why doing so is helping them in various ways during the flight, then that learning and understanding will settle in more concretely. In a metaphorical sense, my first CFI didn't tell me why we were practicing power off stalls at first. He just went into the instructions on how to do them. It wasn't until he later said "we practice these so you can get a better feel for reserve lift in the flare, but also proper full stall recovery" that it actually took hold, and my technique got better.

 

Think of it this way:

  • Grab some scrap paper
  • Draw a vertical line
  • Draw a horizontal line intersecting it
  • Draw a concave line with the apex pointing toward the straight vertical line on the left side
  • Draw a concave line with the apex pointing toward the straight vertical line on the right side
  • Draw a circle around all of that

I described drawing that without any larger framework, so the drawing is similarly abstract. In order to draw a more effective sketch, I should provide you with the framework first: draw the object being used, here. See? It's a lot easier now that you know the context of what I'm asking you to do.

 

It's ALL about framework. ATC truly is the framework that will help all of the tools in the MCP and FMC make a lot more sense, and therefore the knowledge will sink in more effectively and efficiently.

 

 

 


I have a certain amount of envy for those who feel that flight sim is second nature to them, most likely because they fly in real life with a close second to those who use flight sim everyday.  I try to make time for it, but with a sick wife, long hours at work, and trying to maintain an exercise regimen, I don't have the time available to do some deep training, so I whittle away as best I can.

 

I can only speak for myself, but for me, it's equal parts experience, and just a passion for it. On my PPL checkride, my DE told me that she had never seen someone so coordinated in an airplane (and she was a known battleaxe - e.g. discontinued my checkride the first time because my medical only had my middle initial and not the full middle name spelled out), so I'd say there's a certain "second nature" to how I fly, but the knowledge and procedure has all been a matter of practice, practice, more practice, and experience. It might seem odd to hear, but I have a very tough time memorizing things (I'm terrible with names). Over time, I started getting into the habit of conceptualizing checklists to be able to memorize them better, which helped me "memorize" them, even if not exactly. The basic goals of an after landing checklist, as an example, are to clean up the plane, minimize distractions to other pilots (visibly and electronically), and prepare it for an alternate source of power (in a 737/747/777: spoilers stowed, flaps up, TCAS OFF > Mode C only, strobes and landing lights off, and APU on; in a Cessna: flaps up, leave in Mode C, strobes and landing lights off, and alternate power N/A). Now I can run the conceptual checklist, and then verify with the actual checklist, even though the checklist may have more or fewer items than the next checklist I use. That's just my way of making it flexible enough for everything that I end up flying (in and out of the sim), but also to be able to store memory items without forcing myself into rote memorization (which I'm terribly with...I was terrible with dates in history class, but I could write all day about how camels contributed to world trade and the later industrial age :P ).

 

Some of that knowledge and conceptualization took years, though. In the beginning, I was just like everyone else in trying to work with the FMC as if it needed a specific, set, and unchanging flow to use. Later on, as I saw how each piece fell into place with ATC, route planning, and so on, the FMC became a toolbox to address various concerns as those rose up (or ignore entirely in favor of another tool, if necessary), but those concerns rarely pop up without being "in the system." The whole concept of IFR, in general, is pretty confusing, until you start to understand the whole system is built on the idea that if comms or radar are lost, predictability remains. Again, that's tough to conceptualize until you start flying with ATC and start thinking "okay, what is this person going to ask me to do, and what happens if my radio were to suddenly fail?" It won't be easy the first time, but I guarantee you that after your first few flights, you'll be hooked. These lessons are a good primer to get you up to speed, even if you don't do them all on the network in the beginning: http://pilotcerts.laartcc.org/page/ratings.html.

 

I know that's probably more than you wanted to read from me in an entire year, but I'm really hoping that helps nudge you some. I know ATC seems intimidating, and like it would be too much to heap on top of all the other stuff to learn, but I really do think that it actually makes learning the rest of the heap more meaningful, and in some ways, easier.

 

Example:

Why do your STARs have altitude restrictions on them?

What can you use your FIX page for?

Aside from the obvious reason terrain, why might someone set the MCP altitude at anything other than cruise altitude and 0?

 

Fully agreed! One of my favourite approach (on a big airport) is the parkway visual 13L at KJFK. However, there is quite of a portion of radar vectoring to link between the end of the STARs and the final approach especially when turning around KJFK by the North then overseas. When vectoring myself, I find it difficult to get close to a CDA. I usually end up reaching 3000ft too early (or sometimes have to raise the speed brakes fully up...).

 

With a Human ATC to manage the vectors and the descent, it gets way easier.

 

This might be of help when getting into the N90 (NY TRACON) area:

http://tfmlearning.fly.faa.gov/NY_Airspace/NY_Airspace_Pkg/NY_Airspace.swf

 

Click on the "ARR VOR 13L/13R [...]" line to show a representative flight path for the 13 visuals, and the associated vectors to get you there. Note that while the LINDY dumps off at the LGA VOR, there is still a significant amount of vectoring to help kill altitude and keep those arrivals out of the way of LGA and EWR deps. To visualize this, turn on EWR's "ARR 4R, DEP 4L, LGA on 13," and LGA's "ARR River Visual 13, DEP 4" with the JFK ARR VOR 13L/13R still running - and now we all see how complex that area is, and why vectors are so heavily used.

 

Their area is heavily vectored to help cope with all of the airspace concerns, and fleet mix. As such, unless you've worked ATC, or have flown up front up there in the real world, it's tough to see why you're always "too high." That flash animation should help not only give you an example path to self-vector, but also give you an appreciation for the job that they do up there.

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Great! thanks for the link Kyle. It's very instructive.

I have no difficulty to fly and land the parkway visual itself but now I will be able to nail the intermediate vectoring.

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I think I aged 5 years reading Kyle's response. lol :)

 

I appreciate the candid insight Kyle.  It think it is already well known here of your experience and I can see why PMDG picked you up.  They're lucky to have you...actually, it isn't luck.  PMDG only retains the best to put out the best so they can stay the best.

 

Final words...talk among yourselves. :)

 

-Jim

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Great! thanks for the link Kyle. It's very instructive.

I have no difficulty to fly and land the parkway visual itself but now I will be able to nail the intermediate vectoring.

 

You're welcome! Too bad we don't have one for PCT (Potomac TRACON - IAD/DCA/BWI/RIC/CHO/ORF), though our STARs here are less vector intensive. It definitely helped me understand N90 a lot better though!

 

 

 

I think I aged 5 years reading Kyle's response. lol :)

 

I appreciate the candid insight Kyle.  It think it is already well known here of your experience and I can see why PMDG picked you up.  They're lucky to have you...actually, it isn't luck.  PMDG only retains the best to put out the best so they can stay the best.

 

haha - yeah, that was a lot to take in.

 

I call it things aligning properly - whether or not I believe that was a destiny thing, or a luck thing, I haven't yet decided. When I graduated Tech, I spent a summer working at IAD just to get a little bit of money and then set off to PHX to go to a flight academy out there. That all imploded in such a spectacular and disastrous fashion (figuratively, obviously) that I moved back to VA to reset. Had I gone into the industry as a pilot at that time, I probably wouldn't have spent so much time in the sim after 2008, which meant I wouldn't have been in the forum as much, which is how I got into beta testing. The other avenue was being online at the right time to run into one of our beta testers (who is good friends with RSR) while controlling on VATSIM when he was testing the NGX. He was the one who initially got me involved with the DC3 crew, and introduced me to RSR in person. I blame him to a good degree, too.  :P

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Too bad we don't have one for PCT (Potomac TRACON - IAD/DCA/BWI/RIC/CHO/ORF)

 

That would be really nice.  I've done the data collection the hard way when trying to figure out the flow for an area such as SFO.  Flightaware provides (rough) track data for each flight that provides lat/lon/alt/gs data points that I transferred to an Excel worksheet and plotted on xy graph. Do a dozen flights and you can see the pattern for that set of conditions, do a half dozen different conditions and the general picture emerges.  Funny, I had been doing that for at least a week when a VATSIM controller with a friend in the TRACON contacted me and gave me some pictures they use. LOL. The good news is I was getting the picture but bad news was it was time intensive.  This was a few years ago when I was keeping five dozen custom sidstar files up to date, and I was able to include the 'slam-dunk' downwind arriving from North landing either 28.. that downwind is fun to fly.  Anyway, the KIAD flows would be nice and I've never seen how they do it up river at KBWI.

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Anyway, the KIAD flows would be nice and I've never seen how they do it up river at KBWI.

 

PCT's arrival flows are downwind-and-direc-based. As an example, from the north, landing north, the aircraft will be placed on a downwind to receive a final couple vectors to turn them around. From the south, landing north, certain STARs are set up for direct transitions onto the IAPs.

 

The basics are the STARs for IAD. The only true vectoring they do is a mock traffic pattern off of the STARs and onto the extended centerlines.

The CAPITAL8 is the tougher one as it's all vectored.

 

BWI is mostly the same with the SIDs and STARs being the general flows, especially now that they even give some of the info that used to only be in the TRACON SOP: the RAVNN STAR shows the example vectors off of RAVNN for 33 arrivals); while the ANTHM essentially shows how they used to vector off of EMI for the runway 10 (ROKTT leg) and 33 (JABRR leg) flows.

 

DCA is the tougher one since it's wedged in between the other two. The CAPSS is a good example of the south arrival flow, though it's not to scale. KATRN looks like it's east of the airport, but it's actually on the LOC to the field. The leg up to PACKK has them essentially go up to the American Legion Bridge to fly the Riv Vis inbound. The CLIPR does the same but from the NE, placing the aircraft on the "downwind" for either 1 or 19 flows. The rest cover different angles, all on the same principle of placing aircraft on the downwind.

 

 

 

Departures were a little more tricky, but with the new SIDs, it's easier to see. BWI has had hybrid SIDs for its procedures for the longest time, so those I'm sure everyone knows pretty well. With the exception of a couple limited turns right at the beginning, it was along the SID routes. IAD's are now more visible with the SIDs added in the past year. The toughest one to explain to people in the past is now visible in the RIGNZ (what I was describing in Tutorial #1.5 is shown there), though the STOIC and PRYME that popped up in the past briefly showed it. DCA used to be all vectored, and then they put out the NATIONAL departure to help eliminate verbiage from the clearances. I never thought they'd add the RNAVs, but this latest rounded added them, and each one covers what used to just be vaguely outlined as vector guidance in the past SOPs.

 

Still...it would be nice to have the flows visualized all in the same picture like that N90 tool.

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