wardialer
Topic Author
Posts: 1184
Joined: Fri Sep 14, 2001 1:08 pm

### Help On Calculating Course

I have this Flight Planning software which is not too accurate and I only use it to plan my navigations.
But one issue is this.

When planning my route, for example, the Course on the GPS device shows as 72.5 True along with the distance and so on. Thats fine.
But, the software does not show it as exactly being 72.5.

So in this case, what should I enter as course? 72 or 73?

Or for example, if the course shows as 72.6, then how should I round it off?
Would I enter it as 73 or 72?

LONGisland89
Posts: 547
Joined: Sun Jan 22, 2006 3:34 am

### RE: Help On Calculating Course

To answer your example, If it was 72.6, I would round to 73. Rule of thumb when I was in school was to round up anything .5 or higher. Besides, it really doesn't matter too much. You have to travel over 100nm to be 1nm off course if you are .5 degrees off the whole time.

XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

### RE: Help On Calculating Course

Try each one. Whichever is closer, use that one.
Chicks dig winglets.

wardialer
Topic Author
Posts: 1184
Joined: Fri Sep 14, 2001 1:08 pm

### RE: Help On Calculating Course

So what if it shows 90.5?
Should I use 90 or 91?

Or what if it shows 90.4, then should I use 90 instead?

XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

### RE: Help On Calculating Course

.4 is closer to 0, so you round down. .5 traditionally goes to round up to the next whole even though its exactly in the middle.

I would just input in each whole number, look at the result, and see which is actually closer.
Chicks dig winglets.

wardialer
Topic Author
Posts: 1184
Joined: Fri Sep 14, 2001 1:08 pm

### RE: Help On Calculating Course

Well heres the issue. Software tool uses a Tiros 500-Meter map. So its not like Google Earth were I can zoom-in entirely to the exact point of destination.

So with this, I cannot zoom-in any closer.

So just to verify, if my GPS output planning route was shown as 90.5 T, then I would enter 91?

[Edited 2013-07-19 23:00:58]

Starlionblue
Posts: 17970
Joined: Fri Feb 27, 2004 9:54 pm

### RE: Help On Calculating Course

 Quoting wardialer (Reply 5):So just to verify, if my GPS output planning route was shown as 90.5 T, then I would enter 91?

Yes you would. As mentioned above though, half a degree is well within any en route navigation standard. Half a degree is 1 mile off in 120.

AFAIK you don't even need to be accurate to half a degree on a precision approach.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

wardialer
Topic Author
Posts: 1184
Joined: Fri Sep 14, 2001 1:08 pm

### RE: Help On Calculating Course

I guess and would think that it also depends on the type of mapping tool.
For example as mentioned, mapping tool uses only a zooming of max. 500 meter Tiros.
Google Earth uses way more zooming down to the street level.

So, my point is this:

If one would need to use pin-point accuracy like for example 90.555 even, then I would guess a 500 meter map zoom would not be suited for this type of accuracy. So then it would be best to use Google Earth then.

But this is an example though.

But this mapping tool of mine does not let me enter .5 or even .555
Only whole numbers.

zeke
Posts: 11448
Joined: Thu Dec 14, 2006 1:42 pm

### RE: Help On Calculating Course

If you are using it to plan your VFR navigation exercises, forget it, just use the closest degree, and turn your GPS/VOR off.

Learn to navigate by looking out the window for your track and other traffic. Look for features a long way in front of the aircraft. Learn how to correct your track by visually being able to tell if you are off track, and then perform a heading correction.

Light aircraft are incapable of being flown to the accuracy of 1 degree by following the instruments alone, planned speeds are normally out by a fraction, winds are out, instrument errors etc.

Wanting to achieve better than 500 m accuracy in a light aircraft is setting an unrealistic goal for yourself.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News

26point2
Posts: 937
Joined: Wed Mar 03, 2010 6:01 am

### RE: Help On Calculating Course

Oh my....are you using this to plan an actual flight or is this some sort of FlightSim exercise?

What happened to the tried-and-true method of using a map? Why does it matter if you're 1/2 mile of course? Will you then be lost?

Planning software is nice and all but if you can't navigate VFR using pilotage and a map you are doomed.

To add....GPS has evolved during my flying career. 20 years ago we used VLF Omega to find Hawai'i...that's 2200NM without a nav aid. When the OGG VOR came to life after 5 hours we could have been 5 miles off course but we still managed to find the islands. It wasn't a miracle. My advice...put down your gadgets and look out the window.

[Edited 2013-07-20 07:37:18]

vikkyvik
Posts: 12114
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Help On Calculating Course

 Quoting wardialer (Reply 7):So then it would be best to use Google Earth then.

I'm no pilot, but do you know what the positional error tolerance in Google Earth is?

Cause I sure don't.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

skyhawkmatthew
Posts: 475
Joined: Wed Oct 26, 2005 4:42 pm

### RE: Help On Calculating Course

Just round it to the nearest degree. It won't make a jot of difference in the air. Plus, you still need to apply the magnetic variation and that is never going to be a whole number either.

Being one or two degrees out will have absolutely no effect on the outcome of your navex.
Qantas - The Spirit of Australia.

SAAFNAV
Posts: 434
Joined: Wed Mar 17, 2010 5:41 pm

### RE: Help On Calculating Course

 Quoting wardialer (Thread starter): Or for example, if the course shows as 72.6, then how should I round it off? Would I enter it as 73 or 72?
 Quoting LONGisland89 (Reply 1):So what if it shows 90.5? Should I use 90 or 91? Or what if it shows 90.4, then should I use 90 instead?

I'm sorry to be so blunt, but if you struggle to round of 2-digit numbers while on the ground, you should maybe consider another hobby.

If, I hope, you ask for perfection's sake, ask yourself, in how many instances in daily life do you need to use such perfect values and not round off? I can't really think of anything where it makes any noticeable difference.

 Quoting LONGisland89 (Reply 1):To answer your example, If it was 72.6, I would round to 73. Rule of thumb when I was in school was to round up anything .5 or higher. Besides, it really doesn't matter too much. You have to travel over 100nm to be 1nm off course if you are .5 degrees off the whole time.

As said above. Anything below .5, round down. .5 and up, round up.
Also, with the 1-in-60 rule, if you were 1° off course, you will be 1nm off track after 60nm of travel. If you are not able to distinguish any ground feature at 1nm, it means either you are not reading the map correctly, or that you are in inadvertent IMC. Both of which presents way bigger problems than the 1nm off course.

The point of dead-reckoning/map reading is to actually allow yourself to drift off course, pinpoint yourself, calculate your track error, get back to track, and then also be able to calculate the wind to keep you on track until the next major wind change.

There will always be a slight difference between different methods of planning. Even if you do everything on printed maps, slight variations, accuracy of your own plotting or the printers would induce errors.
When you work on a Lambert's Conical Projection Map, you should draw the track and measure the course about midway. There will be a difference between different points on the map. The exact point you use as your reference will create a difference to what someone else will measure.

Some Flight Planning Software systems use scanned copies of topographical maps with a WGS84 overlay. Google Earth can easily display your co-ordinates slightly away from their co-ordinates when you plot positions. The angles and distances will be correct but displaced from yours.

As said above, get your head out of the cockpit, navigate by ground features, and don't worry too much about being exactly overhead the waypoint. Rather get the big picture right, and precision navigation will come later, especially with IF ratings.

Erich

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