# I still do not quite get how to calculate the PNR

hey guys
I am flying over the ocean RN
and I got a bit less fuel than i wanted, so i when to calculate the PRN

however I still do not get what he means by “Out to home, Endurance Hours”
and ECT can somebody explane it i bit more “easy”

3 Likes

PNR = (Ground speed back * Endurance) / (Ground speed back + Ground speed out)

Endurance = Number of hours of fuel on board - reserve fuel

Ground speed back = Ground speed back to initial departure airport

Ground speed out = Ground speed towards destination

Example:
Endurance: 4 hours
Reserve: 45 minutes
True Airspeed = 80 knots
Headwind = 10 knots

Ground speed Back = 80 knots + 10 knots headwind
Ground speed Back = 90 knots

Ground speed Out = 80 knots - 10 knots tailwind
Groundspeed Out = 70 knots

Endurance = 4 hours - 0.75 hours (reserve fuel)
Endurance = 3.25 hours

Take all that information and plug it into the formula:
PNR Time = (90 knots * 3.25 hours) / (90 knots + 70 knots)
PNR Time = around 1.83 hours

5 Likes

Perfect, that’s a great way to break it down!
Thanks for the contribution!

I understand how difficult this can be at first. this is quite complicated stuff to take in, but. with a little practice, it eventually clicks. just keep reading and ask heaps of questions and you’ll get it in no time! :)

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