Flight Planning Confusion...

[akhosh2]

Hi All,
I was doing some comparison between flight planning sites and have compared DUATS, SkyVector and the AOPA flight planner. In each case I was given a different nav log for the same flight...? Your input would be appreciated as to why this may be?

Please the see results below for the following flight plan: KGAI to EMI to KLNS at 21:19z on 1/27/17
(skyvector and duats are fairly close)

 

[genna]

there is about 1-2 min difference(5%).. most likely due to climb/descend approximations being different in each platform. Wind seems to be slightly different too

 

[Caramon13]

I'm not sure I understand the problem. Are you thinking that three separate sites that have quite possibly separate ways of handling routing will somehow all agree on the same route? Or are you questioning the other calcs?

 

[MAKG1]

I *think* you're complaining about the magnetic headings, though you really could be a little clearer on that.

Notice that AOPA has different winds.

 

[coloradobluesky]

The weather is ALWAYS different. Just make sure you carry enough fuel to get to where you are going and check those TFR's! Keep in mind FBO's are sometimes closed on Sundays.

 

[RyanB]

All of those numbers are just estimations. Each source will skew their information slightly different and it may have an extra minute or two here and there. Once you get airborne you can correct the values based on the performance that you're actually getting.

So what's the problem?

 

[bobmrg]

The only thing you can rely on when doing a flight plan manually is True Course, and that is not even shown in the AOPA example, which begins with Magnetic Course. Ah, there's the rub! To convert Magnetic from True you must apply Variation, and the source of that information is very sketchy. The Coast and Geodetic Survey updates its magnetic variation numbers at very long intervals...the one you use may be ten years old...and the agonic lines (lines of equal variation) are very widely spaced: Flying from the Wenatchee, WA area (variation 16.5 E) toward the Seattle area (variation 17.0 E) is approximately 90 miles. My point is that variation, while it cannot be ignored is a guess at best.

That's just an example. As others have noted, the wind information you have to work with is a forecast, and not a very precise forecast at that. True Airspeed and Fuel Burn figures from "the book" were derived by a factory test pilot/engineer flying a brand new airplane with a brand new engine and leaned to the appropriate mixture.

Don't get hung up on precision when the information you are given is so fuzzy. Learn the relationship between the various elements of light planning and accept that each of them (except for True Course) is by its nature subject to error...and if you are not precise in measuring True Course on a sectional chart, even that is questionable.

...and to get back to the root of your question, every publisher of flight logs/flight plans has its own ideas of how things should be done.

Bob

 

[bluerooster]

If you will notice, on just about every navlog, there are spaces for estimated, and actual. The estimated spaces are filled in for you.
It's up to you to fill in the actual spaces while in flight. And there's only a few degrees difference between MC on all of them, I'll wager
that there is a bigger difference noted on your CCC for those headings.
Plus what Bob said>

...and to get back to the root of your question, every publisher of flight logs/flight plans has its own ideas of how things should be done.
[/quote}

 

[GeorgeC]

Hey, another DC local. Welcome to PoA!

 

[sourdough44]

Just another reason for some fuel reserves. There will always be slight variations with any planning then real world results.

 

[dmspilot]

If you want it done “right,” do it yourself.