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I am trying to figure out how to calculate for IFR and VFR for a flight plan example. So from my basic understanding, VFR means you have to add extra 30 minutes to your fuel reserve, and 45 minutes for IFR. So if I wanted to make a flight plan, would I do distance/speed + .5 (for VFR) or + .75 (for IFR)? For instance, if I am calculating that I need an hour's worth of fuel to go a distance of 100 miles at 100 MPH, how would I figure out how much fuel I'd need taking VFR/IFR into consideration?

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    $\begingroup$ Its not that simple. Its 30 minutes for daytime VFR, or 45 minutes for night time. For IFR, you need to be able to fly to your destination, your alternate, and for 45 minutes beyond that, unless weather is above certain minimums. See 14 CFR 91.167 for IFR and 14 CFR 91.151 for VFR, assuming this is FAA (US regulations). $\endgroup$ – Ron Beyer Sep 15 '16 at 20:58
  • $\begingroup$ And for knowing how much fuel to take into consideration, this is simply looking at the cruise performance charts for that particular aircraft and finding the amount of gallons per hour based on the altitude and power setting. For 30 minutes you take half that value, for 45 minutes you take 75% of that value. You really can't calculate how much fuel you need without knowing how much you are burning. Ground distance really doesn't have anything to do with it, other than calculating how much you need to get from dest->alternate, but you also need to know the wind for that. $\endgroup$ – Ron Beyer Sep 15 '16 at 21:06
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For FAA regulations:

Once you've gotten everything planned and it's time to add on the fuel reserve, it is based on the airplane's fuel burn rate from a regulatory standpoint.

If the airplane burns ten gallons per hour, you can easily calculate that you need an extra five gallons, which is 30 minutes of flight duration at ten gallons per hour, for day VFR, and you would need 7.5 for night VFR under FAA regulations, which is 45 minutes of duration, so you would just add those to the total that you calculated that you would need to get to your destination, and you have successfully planned your reserve.

For IFR, you would have to select an alternate if the weather conditions require one, plan your flight to your destination, then to the alternate, and then add on 45 minutes worth of fuel after reaching the alternate, which would be 7.5 gallons after reaching the alternate airport.

This is the regulation for IFR reserve: 91.167

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