IFR Approach Charts Distances

chickencanfly

chickencanfly

Filing Flight Plan
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Chickencanfly
Hello

I am learning how to read IFR arrival plates and finding out that there is a distance variance between the DME Distance and the distance between the fixes and or VORTAC. For example: BAYBI.SUNSS8 arrival.

Distance between PXR (VORTAC) and BAYBI INT based on DME Distances is 59NM.

Distance between PXR and BAYBI INT based on adding distance between fixes is 60 NM (dme 34 +5 +21=60NM)

Why is there 1NM variance?

BTW, I am new to this and studying on my own. It could be a stupid thing on my part, apologies in advance.

Thanks.

Chickencanfly
 

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Without looking at the chart. Rounding?

Add 0.3 to each of the intermediate distances and while .3 will round down the .9 overall will round up.

I don't know if that's the case but that would be my first guess without going online and measuring it GPS coordinate to GPS coordinate.

Also there are more important things to worry about when flying IFR.
 
DME is slant distance, not straight line. Whether it is a factor here, dunno.
 
Chip Sylverne said:
DME is slant distance, not straight line. Whether it is a factor here, dunno.
Click to expand...
I thought that too but a slant distance should indicate further than an across the ground distance. Of course it won't be that much considering.
 
It's a star. Just stay on the assigned route, hit your xing altitudes and any speeds given - no one cares how far it is.
 
It's just rounding. If it was slant range, the DME distance would have to be MORE than the ground distance.
 
chickencanfly said:
Hello

I am learning how to read IFR arrival plates and finding out that there is a distance variance between the DME Distance and the distance between the fixes and or VORTAC. For example: BAYBI.SUNSS8 arrival.

Distance between PXR (VORTAC) and BAYBI INT based on DME Distances is 59NM.

Distance between PXR and BAYBI INT based on adding distance between fixes is 60 NM (dme 34 +5 +21=60NM)

Why is there 1NM variance?

BTW, I am new to this and studying on my own. It could be a stupid thing on my part, apologies in advance.

Thanks.

Chickencanfly
Click to expand...

Magic. Actually it's rounding. If the legs were xx.5(maybe 6, I'm not sure what the cutoff point is) or more, then rounding up would account for it. 33.6 + 4.6 + 20.6 = 58.8 which rounds up to 59. Rounding the individual legs to 34, 5 and 21 gives you 60.
 
Let'sgoflying! said:
It's a star. Just stay on the assigned route, hit your xing altitudes and any speeds given - no one cares how far it is.
Click to expand...
I always have trouble with those 250 kt speed restrictions...
 
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