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felix2

OBS mode for hold pattern - unexpected behaviour

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Hi everyone,

I encountered some unexpected behaviour when trying to use the OBS mode in the TBM900 when trying to fly holding patterns. It seems to me that this is a bug, but maybe I'm doing something wrong. Skip down to "PROBLEM DESCRIPTION" if you want to cut to the chase ;)

A little background: I'm a real world, pilot with a PPL-A close to about 75 hours, VFR only. I have used X-Plane 10 and 11 extensively during my flight training. I use the sim to get familiar with new airports, train for specific situations (e.g. engine emergencies). It has helped me tremendously in training and I can only recommend doing so to any student pilot. After obtaining my license I have continued to train with the sim, even honing my landing skills. The Carrenado PA-28 Archer II captures the real PA-28 that I fly very well, once you fiddle with the joystick curves a little.

I have read a few books on instrument flying and I would love to start my IR soon. I have no doubts that sim training will come in especially handy for that! I have logged quite a few hours flying a Mooney on VATSIM and I'm quite confident using the GNS430 for that now. To make things more interesting, I bought a payware TBM850. On that specific product, the G1000 can't be updated with current charts and doesnt work properly on X-Plane 11. Looking for a replacement, I have followed the development of the X-Aviation TBM900 and I was thrilled when it came out recently.

First of all, I am absolutely amazed by how well this plane is made. Everything from the graphical side of things, the modelling of the systems and even the documentation is just on a superb level! The way using h-shape throttle pattern was implemented is very clever and elegant. I am working in jet engine research and have experience in systems modelling - the way the PT6 is modelled in the X-Aviation TBM900 feels very convincing to me. Amazing stuff :)

PROBLEM DESCRIPTION: I have started to fly various IFR exercises with the TBM900 and X-Plane 11.26. When trying to fly holds on the PINIK wpt near LZSA (Lugano, Switzerland), the problem occurred. The published hold for PINIK is shown below:

1911497050_PINIKhold.PNG.83a09f374a40f8e9ac8c853e0163dbff.PNG

I departed from LSZA using the SID. Before arriving at PINIK, I activated OBS mode to stop waypoint sequencing and keep PINIK as the current waypoint. In the screenshot below, I completed the outbound leg (parallel entry) and the outbound arc. I am using HDG mode to intercept the inbound leg to PINIK:

1_Inbound_HDG_mode.thumb.PNG.77186e7f3c1566a20c933df68ed2988f.PNG

Note that CRS is set to 017°. This should enable me to fly the inbound leg using the NAV autopilot setting. However, when I switch to NAV mode, instead of turning left and intercepting the radial the autopilot will turn right:

2_inbound_NAV_mode.thumb.PNG.75434379274310b2612bbe6e92ee811a.PNG

If I then leave the autopilot in NAV mode and wait, it will  cross the radial and eventually fly away from waypoint, airport and radial:

3_gone.thumb.PNG.f395c50df8c236928e651905078ba546.PNG

The described method of flying a the hold has worked for other waypoints enroute and even at PINIK. I am not able to consistently reproduce the error. My suspicion is that there is a bug in the way the X-Plane/X-Aviation G1000 handles OBS mode. Maybe in some part of the code, the current leg (1320)->PINIK is regarded as a current reference for the autopilot, while it should really be the 017° radial of PINIK?

Am I doing something wrong? Any ideas how to fix this? Is this even the appropriate forum? ;)

Slightly off-topic, I can recommend checking out LSZA and its IGS 01 approach: 6.65° degree glide path, relatively short field, unusual go around and mountains in the VC!

Felix

Edited by felix2

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great to know you are RW pilot.

TBM-900 uses stock LR G1000, so any G1000 bug belongs to LR.

I practiced  a few times half-manual hold in TBM-900,  are you sure your PINiK is activated LEG? because I see it is white color.

and you are in Switzerland, same as China, so how you solved "the latest chart" issue? can we add our own charts manually?

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Felix , I'm probably wrong about this so,  ignore if incorrect.

Not all airports have GPS approaches . In such cases , NDB , VOR , ILS  are the primary navigation aids to an approach and hold. GPS can be used as an aid to get to these final stages .   In order to use these VOR/ILS etc  your nav radios have to be properly tuned . The active frequency in your nav radio (and comm radio ) in the G1000 are the ones closest to the centre of the screen.

With this in mind :

The approach plate suggests its an ils/dme approach  . It doesn't appear to be a designated GPS approach . But I don't have the Lugarno plates so I'm guessing.  If I'm correct the active frequencies you have dialled in on your NAV radios are not 108.9 as specified on the plate. But again I'm guessing , its hard to tell from here because my screen resolution doesn't show these small numbers clearly.

One more suggestion : If the approach is a localizer with a glideslope approach press the CDI  button so that the localizer /glideslope  HSI shows up . It'll be green in color rather than the magenta  , showing in your photos.

Edited by fireone

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My guess with your problem is that there is a problem with the active leg type which prevent the correct use of OBS mode with the waypoint PINIK, maybe because it is not a point to point leg. It may be a limitation of Laminar G1000 though, I do not have enough experience with real G1000.

What I may suggest is to try a direct to PINIK before using that waypoint for your hold.

Or you may use the NAV mode with LOC1 source for the inbound course, and use DME reading or GPS overlay on map to know when you cross PINIK and revert to HDG mode for outbound course of the hold.

I really love the TBM900 but it frustrates me a bit to have a G1000 that is not up to study level like the others systems. Even if that G1000 is surely the best we can have for now in a game sim. 

Pierre

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10 hours ago, cpuwolf said:

I practiced  a few times half-manual hold in TBM-900,  are you sure your PINiK is activated LEG? because I see it is white color.

and you are in Switzerland, same as China, so how you solved "the latest chart" issue? can we add our own charts manually?

PINIK is the next waypoint ("(1320)->PINIK" is indicated in magenta in the PFD). The highlighted radial rotates around PINIK when changing CRS, too. The Indications of the CDI (deviation) are also as expected. I can manually track along the selected radial using the CDI, only the autopilot doesn't get it ;) In the X-Plane forum, someone is pointing at the leg type that might be an issue..

Regarding the latest charts / airnav database: you can update your X-Plane database by putting it into the Custom Data folder, (details: here) How you obtain current data is up to you..

8 hours ago, fireone said:

Felix , I'm probably wrong about this so,  ignore if incorrect.

Not all airports have GPS approaches . In such cases , NDB , VOR , ILS  are the primary navigation aids to an approach and hold. GPS can be used as an aid to get to these final stages .   In order to use these VOR/ILS etc  your nav radios have to be properly tuned . The active frequency in your nav radio (and comm radio ) in the G1000 are the ones closest to the centre of the screen.

With this in mind :

The approach plate suggests its an ils/dme approach  . It doesn't appear to be a designated GPS approach . But I don't have the Lugarno plates so I'm guessing.  If I'm correct the active frequencies you have dialled in on your NAV radios are not 108.9 as specified on the plate. But again I'm guessing , its hard to tell from here because my screen resolution doesn't show these small numbers clearly.

One more suggestion : If the approach is a localizer with a glideslope approach press the CDI  button so that the localizer /glideslope  HSI shows up . It'll be green in color rather than the magenta  , showing in your photos.

@fireone: Thanks for wrapping your head around the approach. Unfortunately, I have not made it clear enough that I am not flying the approach. I am starting out flying the SID and then trying to hold on PINIK. I have tried the approach, it works like a charm :) Send me a message if you are interested in the plates.

1 hour ago, Sweet19blue said:

My guess with your problem is that there is a problem with the active leg type which prevent the correct use of OBS mode with the waypoint PINIK, maybe because it is not a point to point leg. It may be a limitation of Laminar G1000 though, I do not have enough experience with real G1000.

What I may suggest is to try a direct to PINIK before using that waypoint for your hold.

Or you may use the NAV mode with LOC1 source for the inbound course, and use DME reading or GPS overlay on map to know when you cross PINIK and revert to HDG mode for outbound course of the hold.

I really love the TBM900 but it frustrates me a bit to have a G1000 that is not up to study level like the others systems. Even if that G1000 is surely the best we can have for now in a game sim. 

Pierre

I think you might be onto something. That's close to what someone said in the x-plane forums. I will try doing a D->Pinik and also inserting PINIK somewhere in the flight plan. It just doesnt make sense to me, since with my method, I can activate OBS mode, it will give me course deviations as needle deflections and/or xtk distances and I could fly by that manually. Why should the autopilot A: not be able to do it and B: not give any warning or error if it's not? The way the system behaves, it creates risky situations. (I realise that I am not sitting in an actual plane, just saying ;))

Your proposed method of using LOC1 will surely work. But doing so in an actual flight would require you to anticipate the problem with OBS mode. I could also imagine situations where this bug occurs and there is no localiser.

Finally, I agree with your comment about the G1000 not being on par with the rest. But when I tried to find a simulator and plane offering nice graphics, 3D cockpit and the option to do IFR stuff / VATSIM some year or two ago, it was a lot worse. I feel like its getting closer every day :)

 

Thank you all for your thoughts!

Felix

Edited by felix2
grammar

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1 hour ago, felix2 said:

In the X-Plane forum, someone is pointing at the leg type that might be an issue..

That guy responding to you in the XPlane forum is Philipp Ringler, he's responsible for all the navigation stuff at Laminar Research. 

So, if he say so you can at least be sure it's not a bug, but intended to be that way in xplane. Of course that doesn't mean it's like the real life G1000, but as he's a CFI in real life one could assume he knows what he's talking about. 

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33 minutes ago, RobW05 said:

So, if he say so you can at least be sure it's not a bug. 

I disagree. This can't be the intended behaviour. Not when everything else follows a rigid concept.

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I just meant you could stop bug hunting, as the responsible Laminar team member told you he designed it that way. But of course you can disagree with him if it's correct or not. :)

Edited by RobW05

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Ok I see what you mean - I traced the problem to its root, so to say ;) Maybe I should call it a feature request from now on :D

Jokes aside, it could very well be an unintentional behaviour (bug) on top of his intended implementation. If you have time to waste, try it in the sim!

 

Edited by felix2

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Update: As of X-Plane 11.30 Beta 7, the G1000 won't let you activate OBS mode on those "CA" type legs, so no source of error anymore.

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I agree with @felix2 this is a bug and if not its a wrong behaviour. The AP should follow the HSI course on OBS mode and not the opposite course. Unfortunately an excellent plane have been coupled to a not that perfect XP autopilot function. It that was the RXP 430 or 750 its would have been following exactly what you intended to do in the hold.

By the way the Lugano IGS is amazing, looks like a dive and if you are not fast enough after PINIK and end up above the GS better turn around for another approach because you will never catch it.

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