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GCarlson

DME ARC in MD-11

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Is there a way to program a DME arc into the FMS? I read through the FMS guide, and didn't see anything.Thanks, Gary Carlson


Gary M. Carlson

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It has to be programmed into the sidstar procedure file, and even then the arc is a series of segments. The script language is the same as 737/747. Hope to see ARINC 424 data in the NGX, which includes the AF leg (arc to fix).


Dan Downs KCRP

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>It has to be programmed into the sidstar procedure file, and>even then the arc is a series of segments. The script language>is the same as 737/747. Hope to see ARINC 424 data in the NGX,>which includes the AF leg (arc to fix).Oh really? What a shame. I was hoping that this would have been sorted with the MD11 release. It makes creating SID/STAR arcs cumbersome and lacks realism when observed in the FMC and on the HSI.If the AF leg type is going to be used in the NG then is there a chance that this might be a available to be included with the first MD11 service pack or even maybe the 747?


Cheers

Steve Hall

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>Is there a way to program a DME arc into the FMS? I read>through the FMS guide, and didn't see anything. Gary,If its not programmed in a SID/STAR,Yes there are two ways to do it, with a bit of work:Via the REF - Defined Waypoint page, you are able to create a series of waypoints as needed. you also can give these waypoints a name as you like.After this has been done, enter these points into the F-PLN LSK'sVia F-PLN directly:In the scratchpad enter a Place/Bearing/Distance.Line select it to an LSK.Continue to do this for as much points you need; Points will autoname PBDxx in sequence.Regards,Harry

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It is actually not that hard to fly a DME arc with the RMI feature provided on the ND... just keep the wing pointed to the station at the right distance. Normal procedure is to fly a heading until the pointer is behind about 5 deg and turn 10 deg towards the station. Keeping this up with a turn about every 10 deg, adjusting earlier or latter to keep the distance within a mile of the desire value. I think everyone flew segmented arcs until all this automation came along. My first one was in a Beech Sierra at night in the WX at Gulfport MS with no ATC RADAR... the darn DME was located on the right side of the PAX and hard to see (it wasn't even a digital readout, just a meter). The PAX was freeking out, claiming she saw another airplane in the clouds (probably and antenna tower light below us). ATC asked me if I had turned final yet about 5 deg after I passed the final course... I was so focused on the arc procedure I passed the final a little... not too far tho. We survived.


Dan Downs KCRP

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Good thread. Because of this thread, I am going to fly the ARC DME approach into MGGT tonight. (In the MD-11). I hope that big bird can do that sweeping turn.RhettFS box: E8500 (@ 3.80 ghz), AC Freezer 7 Pro, ASUS P5E3 Premium, BFG 8800GTX 756 (nVidia 169 WHQL), 4gb DDR3 1600 Patriot Cas7 7-7-7-20 (2T), PC Power 750, WD 150gb 10000rpm Raptor, Seagate 500gb, Silverstone TJ09 case, Vista Ultimate 64ASX Client: AMD 3700+ (@ 2.6 ghz), 7800GT


Rhett

i7-8700k @ 5.0 ghz, 32 GB G.Skill TridentZ, 1080Ti, 32" BenQ, 4K res

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Guest jbos

The place/bearing/distance method is by far the best way, since the place and distance stay the same for each fix along the arc. Only the bearing changes!And if you really want to be precise with the segments, multiply your distance by the following:10 degrees - 1.00220 degrees - 1.00725 degrees - 1.01230 degrees - 1.01745 degrees - 1.04E.g. if you are following a 25 DME from the 50 degree to the 110 degree radials, and you decide to use four segments, your points would be:FIX,50,25.2FIX,70,25.2FIX,90,25.2FIX,110,25.2They are 20 degree segments, so multiply the distance like this: 25 * 1.007 = apprx 25.2 You will be 0.2 outside the arc at the end of each segment, and 0.2 inside the arc at the middle of each segment.

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Hi there,there is a third way to fly a DME ARC. In fix page, enter the VOR DME identifier, then enter a distance.This will draw a dashed circle on the ND centered on the VOR DME.Then you try to follow the dashed line in heading select mode.Sometimes I used this method when I don't have time to build the DME ARC by using Place/Bearing/Distance waypoints (ATC instructions not planned for example)>>Is there a way to program a DME arc into the FMS? I read>>through the FMS guide, and didn't see anything.>> >>Gary,>If its not programmed in a SID/STAR,>Yes there are two ways to do it, with a bit of work:>>Via the REF - Defined Waypoint page, you are able to create a>series of waypoints as needed. you also can give these>waypoints a name as you like.>After this has been done, enter these points into the F-PLN>LSK's>>Via F-PLN directly:>In the scratchpad enter a Place/Bearing/Distance.>Line select it to an LSK.>Continue to do this for as much points you need; Points will>autoname PBDxx in sequence.>>Regards,>Harry>>>>>>>


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Location : FMEE

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I think I will have to try place/bearing/distance, because just exiting the airway and loading the STAR and approach resulted in a non-sensical approach. -- and even with tweaking the MD-11 couldn't handle the sharp turn to final on autopilot.Consequently, I had to manually tweak the F-pln. The result was something that did not work; the aircraft was not able to turn quickly enough to do the ARC DME at Guatemala City. The second time I tried it, I disco'ed the autopilot/ATS and of course was able to execute the landing.I'll have to try place/bearing/distance and see if I can get it to work. Maybe some approaches are not appropriate for autopilot or CATII/III etc.?RhettFS box: E8500 (@ 3.80 ghz), AC Freezer 7 Pro, ASUS P5E3 Premium, BFG 8800GTX 756 (nVidia 169 WHQL), 4gb DDR3 1600 Patriot Cas7 7-7-7-20 (2T), PC Power 750, WD 150gb 10000rpm Raptor, Seagate 500gb, Silverstone TJ09 case, Vista Ultimate 64ASX Client: AMD 3700+ (@ 2.6 ghz), 7800GT


Rhett

i7-8700k @ 5.0 ghz, 32 GB G.Skill TridentZ, 1080Ti, 32" BenQ, 4K res

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>And if you really want to be precise with the segments,>multiply your distance by the following:>>10 degrees - 1.002>20 degrees - 1.007>25 degrees - 1.012>30 degrees - 1.017>45 degrees - 1.04>Where do those numbers come from?Paul

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>>And if you really want to be precise with the segments,>>multiply your distance by the following:>>>>10 degrees - 1.002>>20 degrees - 1.007>>25 degrees - 1.012>>30 degrees - 1.017>>45 degrees - 1.04>>>>Where do those numbers come from?:-lolHe, he, they are represent the inverse cosine of those angles, except that our friend got them wrong, here are the correct numbers, perhaps he messed up number of zeros(??):10 deg. - 1.0220 deg. - 1.0625 deg. - 1.130 deg. - 1.1545 deg. - 1.4They represent your DME factor-distance at the end of each straight line segment. BUT the main point is they are completely useless for a pilot. No pilot in real world flying a DME arc would ever need to use those numbers, no pilot would ever want to perform this sort of trigonometry while flying IFR.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg


Michael J.

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Guest jbos

Trigonometry. The idea is that you want your segments to error by the same distance both inside and outside the arc. So, each half-segment will be a right triangle, with hypotenuse = D*(1 + x) and leg = D*(1-x), where D is the desired DME and x is the "error" fraction.So you get:cos(A/2) = D(1-x)/(D(1+x))Cancel the D's:cos(A/2) = (1-x) / (1+x)Then solve:cos(A/2) + x * cos(A/2) = 1 - x.(1 + cos(A/2)) x = 1 - cos(A/2)x = (1 - cos(A/2)) / (1 + cos(A/2))And x is 0.002 for 10, 0.007 for 20, 0.012 for 25, etc as in the table I gave. And if you want to take it a step further and add in the 1, you can do that too and actually simplify the expression some more:1 + x = 1 + (1-cos(A/2))/((1+cos(A/2))1 + x = (1+cos(A/2))/(1+cos(A/2)) + (1-cos(A/2))/(1+cos(A/2))1 + x = 2/(1+cos(A/2))

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Guest jbos

Actually you need to use half the angle. And it's not really 1/(cos) but 2/(1+cos) -- 1/cos is too much since it will keep you completely outside the arc whereas you want to be equally inside & outside. I did the derivation in another post. Just gut-check your numbers, if it were really 1.4 for a 45-degree, that is saying that you would need to go 8 miles outside a 20 DME arc doing 45-degree segments.And no-one would have a trig table in flight, but then 99% of the time, the ATC would vector you to final. Even if you did have to fly the full approach and it wasn't in the computer, you wouldn't be typing in waypoints by hand. You would use the HDG dial rather than the LNAV. So hand-programming a DME arc into the FDC is academic anyway.But assuming you do want to emulate it in the FDC for some reason, you can use 10 degree segments and pretty much ignore this adjustment. But if you are intending to save yourself some typing and do 30 or even 45-degree segments, you probably should. Otherwise, you will end up quite a bit inside the arc. With the adjustment, you will drift between 4% inside and 4% outside the arc on 45-degree segments. Without, you will go up to 8% inside the arc. That's 1.6 miles inside a 20 DME which is probably more than you want to be.

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