FMS - ALT-Restriction-Waypoints

[Stefan]

Hi Philipp,

after some testing, there seem still to be significant issues in the processing of OVFLY- and restriction-Waypoints.

maybe the problems i noticed, are the same as in another open thread about STAR-problems.

When i fly the ABIRI1G-Departure from LOWG, which consists of an overfly-Waypoint GRZ-NDB followed by an altitude restriction 2200A and a right-turn, (in the chart described as: after passing GRZ and above 2200ft turn right...), the 2200A-Waypoint is not sequenced before i have passed GRZ. After passing GRZ - which happens usually above the 2200-restriction-altitude - the 2200A-waypoint is not sequenced, but acts as a 2200-below-restriction.

I tried to descend below 2200-ft, which caused sequencing of the 2200A-waypoint (which is another strange behaviour, because i would have expected, i had to climb again through 2200 to trigger the restriction-waypoint).

IMHO the correct behaviour would be: when passing 2200ft before passing GRZ, the 2200A-wpt should be removed from the list, or th 2200A-wpt should be processed immediately after passing GRZ.

would you pls have a look at this. i added the flightplan of the ABIRI1G-departure to this post.

thanks,

Stefan

ABIRI1G.txt

Edited May 30, 2012 by Stefan

[Japo32]

If you mean the way the FMS process the Navigraph data to input the points with its altitude restrictions, then Philipp will answer this one.. BUT if you are saying the plane is not following the altitude restrictions, this plane has not VNAV autopilot, so you have to fly it manually. Only those Altitudes restrictions that are shown in the FMS when importing a SID or STAR are for informative pilot eyes only. The pilot is the one that has to guide the plane through them.

[Stefan]

Hi Javier,

i do not mean VNAV - i mean the interpretation of the nav-data. the 2200-above-waipoint is not sequenced (and the following right-turn initiated) , although i'm far above this altitude.

Regards,

Stefan

[cessna729]

Hi Stefan, Have you had a look at the LOWG.xml file in your LevelD folder to see how Navigraph have coded the ABIRI 1G SID? I'm not at my X-Plane PC at the moment so cant check, but the JEPPESEN LOWG/GRZ ABIRI ONE GOLF SID I have to hand (it's a bit old, 27May09) says;

"Climb on 168 deg track, when passing GRZ-NDB and 2200ft turn RIGHT 270 deg heading, intercept GRZ R-238 to ABIRI." And it also states that "a minimun climb gradient is required of 468ft per nm (If unable to comply to use SID GRZ-2X)", and "all initial turns with MAX 205kts and a bank angle of at least 20deg."

IMHO, it appears that the path GRZ-VOR to initiation of the RIGHT turn should Terminate upon two things happening "passing GRZ-NDB and 2200ft"

Does it look like the Navigraph data complies?

My guess is Navigraph have coded it as seperate paths;

1st path terminates passing GRZ-NDB, then 2nd path contant Hdg till terminating at 2200ft. hense the CRJ-200 (good-ol-girl that she is) just does what she's been told to do (by Navigraph data), but if you pass 2200ft before GRZ-NDB, the 2200A waypoint never gets triggered.

One thing the CRJ-200 may not like is if Navigraph use the same waypoint names "GRZ" for the VOR and "GRZ" for the NDB and possibly even (GRZ) for the conditinal waypoints (as in previous posts).

cessna729.

Edited May 30, 2012 by cessna729

[Stefan]

cessna729,

thx for your investigations.

as i can remember, i had these problems never, when using vasFMC - which is based on the same nav-data.

i will try to cross-check this and check the nav-data again. but one thing, i am sure, is not correct: that the 2200A waypoint is triggered, when i descend BELOW 2200ft.

regards

stefan

[cessna729]

Sorry for double post, having problems with a firewall!!

cessna729.

Edited May 30, 2012 by cessna729

[cessna729]

No problem, let you in on a secret I've been working on a pet theory that these and a few other "CRJ-funnnies" may be due to the application of Magnetic Variation on FIXED and conditional waypoints, but as yet I havn't gathered enough evidence so far (trying to figure out all the MV's and get hold of the real MV of record is a pain), but I can tell you what the MD is at LOWG is this instant!! "click here ! but with my luck I'm more than likely barking-up-the completely wrong tree. . The "real world" has had its "funnies" to.

cessna729.

Edited May 30, 2012 by cessna729

[philipp]

I think the answer to this is already given in the second half of that post:

Plus, you both please check your private messages.

Philipp

[cessna729]

My guess is Navigraph have coded it as seperate paths;

1st path terminates passing GRZ-NDB, then 2nd path contant Hdg till terminating at 2200ft. hense the CRJ-200 (good-ol-girl that she is) just does what she's been told to do (by Navigraph data), but if you pass 2200ft before GRZ-NDB, the 2200A waypoint never gets triggered.

My guess was correct, I've just checked on my 1202 cycle Navigraph data for LOWG.

On that version they have the ABIR2G SID for Rwy 17C, and WP1 is a ConstHdgtoAlt 1520ft, WP2 is the GRZ NDB, WP3 is the ConstHdgtoAlt to 2200ft, and WP4 is the Intc which IMHO is unfortunate as the JEP published SID states that "a minimun climb gradient is required of 468ft per nm (If unable to comply to use SID GRZ-2X)", LOWG elevation is approx 1120ft, so 2200-1120=1080, therefore the a/c has to climb 1080ft at a climb gradient of at least 468ft per nm. So it would take 1080/468= only 2.3 nm and yes you guessed GRAZ NDB is at least 3.5nm from the end of Rwy17C and approx 4.3nm from the mid point of 17/35. So the a/c will pass 2200ft before passing the NDB (based on my quick reading of the published SID). Therefore if Navigraph had coded the NDB before the 2200ft Alt Restriction there most likely wouldn't have been a problem.

Note: It's now very late so I've just had time to do one quick test flight and take the mesurements off X-plane's Local region map, I still have to dig out the books and check the expected single engine climb performance requirements for the SID specs. . But that's for another day.

cessna729

Edited May 30, 2012 by cessna729

[Stefan]

i did some tests with vasFMC (i got it working with XP10! :-)) based on an 11xx-Cycle - and it processed the (2200) wpt correctly immediately after passing GRZ-NDB. I will have to cross-check the nav-data with the 1202 of the CRJ for more detailed information.

the second thing i found when engaging the AP on the FMS a little bit late, after passing the 1520A-restriction alt, but before passing GRZ-NDB. FMS did not trigger the 1520A-wypoint anymore. So it seems FMS triggers the Restriction-points only in case of a TRANSITION THROUGH the restriction-alt, but not when it is ALREADY ABOVE the xxxxA-altitude, which IMHO would be the correct behaviour.

Then the implementation of the nav-data - as cessna described - would not have any influence on the fms-processing.

[cessna729]

So it seems FMS triggers the Restriction-points only in case of a TRANSITION THROUGH the restriction-alt, but not when it is ALREADY ABOVE the xxxxA-altitude,...

Hi Stefan, I wonder if the FMS's need to see a "transition-through" and not skiping/removing WP if trigger allready passed also applies to lateral limits? i.e. contant heading till radial or dme ect? or is this "feature" limited to alt?

cessna729.

[Stefan]

i don't no if this "feature" is limited to alt - but for me it looks like, the not yet passed GRZ wpt "hides" the 2200A-point, so that it cannot be triggered. and as you can see at the LOWG-departure, flying above 2200 after GRZ doesn't trigger the 2200A.

After my "quicktest-route" LOWG-LOWK works perfectly, i will try some advanced approaches and we'll se, wat the lateral nav does ...

[cessna729]

as you can see at the LOWG-departure, flying above 2200 after GRZ doesn't trigger the 2200A.

When I flew your LOWG SID last night, my CRJ-200 set heading to 167 deg and climbed at 185kts to 8000ft with WP (2200) maintaining the same relative posittion stitting approx 10nm infront of the aircraft all the way, till I gave up at 118nm

Well that's enough fun "lunch-time" is over, back to work.

cessna729.

[cessna729]

After my "quicktest-route" LOWG-LOWK works perfectly, i will try some advanced approaches and we'll se, wat the lateral nav does ...

Hi stefan, the LOWK ILS28 approach with a KFT Transition looks advanced to me (2 step down procedure turns), cor you must be "hard core IFR pilot" if you don't think that's advanced!!

The "real plate" looks good.

The CRJ had a little problem with the 1st proc turn (shown in yellow).

You can see the CRJ's flight path (the thin violet line in the plot below), it flew the procedure quite well, and it's not realy to blame for the miss shaped 1st Proc Turn. It tried to do what the Navigraph 1206 data said but as the AppTr_Waypoint ID="3" was set to "Fly-by" and physically close to the next WP, the CRJ "flew-by" the full procedure turn, it did better on the 2nd Proc Turn. (see below).

Question for philipp: On the current version of the CRJ and Navigraph data, how close is a "Fly-by"? and what's the minimun seperation between WP to keep the CRJ happy?

cessna729.

[Stefan]

hi cessna,

since my home-location is lowg, i am quite familiar with the routes around LOWG :-). But as you can see, the route LOWG - LOWK covers a wide range of procedure-elements, which are good for training and testing.

and you have to fly very exactly an concentrated, because you are flying between high mountains and things happen very quickly.

LOWI via RTT LLZ(offset)/DME-approach with visual turn to final is a bit more challenging, also LOWS departures and arrival. Cuzco in Peru is very nice, but my absolute favourite approaches/departures are at LGSM (VOR/DME, visual turn to final, heavy crosswind and turbulence as in real-world...)

[cessna729]

my absolute favourite approaches/departures are at LGSM (VOR/DME, visual turn to final, heavy crosswind and turbulence as in real-world...)

I'll give it a go sometime When i used to intruct for a living, a long,long long time ago in Texas "Pan-Handle" USA, we didn't run-into many mountains, but sure found alot of "turbulence", they didn't call it "Tornado-Alley" for nothing So-much-so, we used to do most of our IFR training at night or early morning cos it was so bad in the afternoon

cessna729.