Aviation math: 52 + 20 = 73?

You're using NACO charts...they use very large values of "2" on the NACOs.
 
DME distance is slant line, so your extra mile may reflect that, while the other distances (in parens, not shown in the elongated D) are leg distances, not DME distances.
 
I went to an ASF safety seminar last night. I had a discussion with a couple others regarding GPS navigation where one spoke of stating positions.

He was saying he had heard a controller in another seminar ask pilots to speak in whole numbers. Apparently, the more exact distance displayed has pushed some to state "9.6 miles East XXX" or even "9.62 miles East XXX."

Obviously, simple whole numbers are preferred. They create less confusion and allow less room for error. The same is no less true on an IAP. Even though an approach plate is indicating DME in tenths, only call out whole miles when requested.
 
Yup, Ed's right.

Using the lat-longs off the chart, and this lat-long distance calculator:

WINDU to BLEWE

Distance between 31 31'83"N 97 4'95"W and 31 12'54"N 97 12'54"W is
20.4968 nautical miles

CWK to BLEWE
Distance between 31 12'46"N 97 12'54"W and 30 22'71"N 97 31'79"W is
52.4067 nautical miles


WINDU to CWK
Distance between 31 31'83"N 97 4'95"W and 30 22'71"N 97 31'79"W is
73.0284 nautical miles
 
How 'bout we're both right?

My point was that on a chart where you see a distance given, that distance is a leg distance, and may not correspond to a DME reading unless it's in the proper symbol (with the distance enclosed in a D shape).
 
TMetzinger said:
How 'bout we're both right?

My point was that on a chart where you see a distance given, that distance is a leg distance, and may not correspond to a DME reading unless it's in the proper symbol (with the distance enclosed in a D shape).
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Yup, I think your point makes sense as well. However, on slant distance, at what altitude do they 'figure' you're at when they plot the 'distance' inside the "D" shape?
 
TangoWhiskey said:
Yup, I think your point makes sense as well. However, on slant distance, at what altitude do they 'figure' you're at when they plot the 'distance' inside the "D" shape?
Click to expand...
Obviously, the further out you go the less significant it is. But, it shouldn't be a major concern. The closer point where it does have more of an effect is during approach. If one is focusing so closely on tenths of a mile in DME indications, who, at that point is flying the airplane?
 
TangoWhiskey said:
Yup, I think your point makes sense as well. However, on slant distance, at what altitude do they 'figure' you're at when they plot the 'distance' inside the "D" shape?
Click to expand...

Yanno - lemme go look at the NACO chart guide again. I want to be sure I've got the purpose of the D shape correct.
 
KennyFlys said:
I went to an ASF safety seminar last night. I had a discussion with a couple others regarding GPS navigation where one spoke of stating positions.

He was saying he had heard a controller in another seminar ask pilots to speak in whole numbers. Apparently, the more exact distance displayed has pushed some to state "9.6 miles East XXX" or even "9.62 miles East XXX."

Obviously, simple whole numbers are preferred. They create less confusion and allow less room for error. The same is no less true on an IAP. Even though an approach plate is indicating DME in tenths, only call out whole miles when requested.
Click to expand...
Brief aside, was at a FAASTeam meeting a couple of months back with the controllers from KPWK, and it came out that when they give distances (e.g." report 2 SW") they are thinking of the distance from the approach end of the runway, or even the edge of the airport. That is NOT the same, of course, as the distance from the center of the airport that's reported by most GPS devices.
 
TMetzinger said:
Yanno - lemme go look at the NACO chart guide again. I want to be sure I've got the purpose of the D shape correct.
Click to expand...


OK, I've confirmed that the D shape is to give DME distance (and here's the important point) WHEN NOT OBVIOUS. So that helps the pilot know that even though the two legs may appear to total 72 NM, the fix is at 73 DME.

Source:
NACO 7th IAP Symbols guide.
 
gprellwitz said:
Brief aside, was at a FAASTeam meeting a couple of months back with the controllers from KPWK, and it came out that when they give distances (e.g." report 2 SW") they are thinking of the distance from the approach end of the runway, or even the edge of the airport. That is NOT the same, of course, as the distance from the center of the airport that's reported by most GPS devices.
Click to expand...
Agreed. It should be from a specific fix or visual reference. To state a distance to Hartsfield could be a variance of two miles or more.
 
TangoWhiskey said:
That makes sense, Tim....
Click to expand...

It's got nothing to do with slant range, which BTW are dependent on altitude above the ground station and therefore no single number could represent it on a chart. EdFred's answer is almost certainly the correct one (even though it came from Ed :p).
 
calculated slant (DME) distance (by pythagoras at 13,000')=72.0318, not 73
from Airnav:
CWK-BLEWE=52.33
BLEWE-WINDU=20.39
CWK-WINDU therefore=72.72

it is a rounding error. also, the small open arrows indicate that the "leg length" of 52 can be identified by DME
 
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