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## PNR Distance

• Posts: 167

### jukzizy created the topic: PNR Distance

Find the distance to PNR for a charter day vfr small piston flight from alpha to bravo:

Distance 388NM
TAS 145KTS
W/V 230*T/40KTS
VARIATION 8E
Please John can you help check this if I'm doing the right thing?

ALPHA has Tempo holding
Bravo has inter holding
Fuel flow is 92L/hr
Taxi 15L
Fuel at start up 475 Litres
ETAS= 139KTS

Flight fuel- 334.5L
Variable- 1.1
Holding (Tempo) 92L
Taxi- 15L
Fuel on board at start up- 475L

Se= 334.5÷92=218 minutes

PNR= (218×140kts)÷290
=105 minutes

Distance= speed × time
138×105
= 241.5 NM

• Posts: 168

### Carello replied the topic: PNR Distance

How did you get the ETAS, was it given?
How did calculate G/Shome and the G/Sout?

• Posts: 167

### jukzizy replied the topic: PNR Distance

cross wind was 31kts which will align to 16* drift

Etas= 145cos 16=138kts

The Etas was nit given but I did calculted it since the track was given and W/V

• Posts: 168

### Carello replied the topic: PNR Distance

For some reason you did not include the track in the initial question.

• Posts: 168

### Carello replied the topic: PNR Distance

It has been 30 years since I've done one of these!

Usable Fuel @ Start Up = 475 L
Start & Taxi = 15 L
60 Holding @ Return Airport = 92 L

115% Flight Fuel = 475 - 15 - 92 = 368 L
100% Flight Fuel = 334.5 round down to 334 L

Fuel Flow = 92 L/hr
Endurance = Flight Fuel/Fuel Flow = 334/92 = 3.63 hrs

TPNR = (Endurance x G/Shome)/ (2 x TAS) = (3.63 x 140)/(2x145) = 1.75 hrs

DPNR = TPNR x G/Sout = 1.75 x 138 = 241 nm

Given that the question did not provide a track, I've used your G/S home and G/S out

Se= 334.5÷92=218 minutes
Mathematically this is nonsense. 334.5/92 = 3.63 hrs not 218
Why would you convert to minutes ?

PNR= (218×140kts)÷290
=105 minutes

Mathematically this is nonsense. (218×140kts)÷290 does not = 105
Why are you working in minutes?

Distance= speed × time
138×105
= 241.5 NM

Mathematically this is nonsense. 138×105 does not = 241.5
Why are you working in minutes?

• Posts: 167

### jukzizy replied the topic: PNR Distance

I work in minutes because our instructor always use minutes that's why I'm confuse

• Posts: 167

### jukzizy replied the topic: PNR Distance

jukzizy wrote: Find the distance to PNR for a charter day vfr small piston flight from alpha to bravo:

Distance 388NM
TAS 145KTS
W/V 230*T/40KTS
VARIATION 8E
Please John can you help check this if I'm doing the right thing?

ALPHA has Tempo holding
Bravo has inter holding
Fuel flow is 92L/hr
Taxi 15L
Fuel at start up 475 Litres
ETAS= 139KTS

Flight fuel- 334.5L
Variable- 1.1
Holding (Tempo) 92L
Taxi- 15L
Fuel on board at start up- 475L

Se= 334.5÷92=218 minutes

PNR= (218×140kts)÷290
=105 minutes

Distance= speed × time
138×105
= 241.5 NM

Track is 310*M

• Posts: 168

### Carello replied the topic: PNR Distance

Correction to my previous working - I neglected to account for the Fixed Fuel reserve

Usable Fuel @ Start Up = 475 L
Start & Taxi = 15 L
60 Holding @ Return Airport = 92 L
FR 30 min @ 92 L/hr = 46 L

110% Flight Fuel = 475 - 15 - 92 - 46 = 322 L
100% Flight Fuel = 292.7 L round down to 292 L

Fuel Flow = 92 L/hr
Endurance = Flight Fuel/Fuel Flow = 292/92 = 3.17 hrs

TPNR = (Endurance x G/Shome)/ (2 x TAS) = (3.17 x 140)/(2x145) = 1.53 hrs

DPNR = TPNR x G/Sout = 1.53 x 138 = 211 nm

Given that the question did not provide a track, I've used your G/S home and G/S out

• Posts: 167

### jukzizy replied the topic: PNR Distance

Thank you very much for you help..appreciated..

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 555

### John.Heddles replied the topic: PNR Distance

In the same vein as a comment offered for another thread, one really needs to be careful when using the (2 x TAS) approximation for (G/S out + GS home) if you have much drift. Generally, we consider the case where wind speed is a high fraction of the TAS to be the situation which raises concern and for which the person running the sums needs to be on his/her toes. My philosophy is not to set yourself up to fail but, rather, always use the groundspeed values - a bit like the approximation for ETAS on the Jepp for small drift angles where cos(drift) gets closer to 1.0. Why bother straining your brain with extra stuff to remember and figure on the fly ?

It is illustrative to rework the calculations for this example (where drift is significant - up around 16 degrees) using the calculated groundspeed values just to see the sort of errors which can creep in using the approximation. Sure, the approximation is fine if the drift angle is small but this is not always the case.

I work in minutes because our instructor always use minutes that's why I'm confuse

That's not really a problem. You pick whichever you prefer of hours or minutes and run with that unit. Really no difference which you might prefer - it is only a matter of choice. Keep in mind that, if you run the calculations on your whizz wheel, rather than that dreadful electronic calculator gadget, it is much easier as you have all these calculations set up as easy proportions - one of the reasons I prefer to run my calculations on the slide rule. (Then again, I was weaned onto slide rules at a very young age when we didn't have PCs and electronic calculators were big, bulky things which cost a mint so it's pretty easy for me to say that ..)

Engineering specialist in aircraft performance and weight control.