Hi Bob and Richard,

I came upon an question which I have scanned and worked in pencil.

It relates to PNR, which as we know is PNR = (Safe Endurance x GS Home) / 2x TAS

Now the question is show attached, but basically is as follows:

Fuel on Board 150L
Holding req at departure aerodrome 30 mins and destination aerodrome 60 mins (total 90 mins)
Holding fuel burn same as cruise burn which is 60 litres per hour

Normally I would work this question as:

150L -
Fixed Reserve (45 mins at cruise) of 45L
Allowances (Taxi) of 5L
Holding Fuel (90 mins at 60 lph) of 90L

Leaves me with 10 Litres of Flight fuel!!

Now to calculate the PNR I need to work out the safe endurance, which I can either work out based on flight fuel (which is usual) or in this case I could add in the Holding Fuel and work safe endurance out with that in the mix as well, but the latter doesnt seem right to me.

Yet in your worked example you show 150-5-45-30L and I am wondering how in heck did you pull the 30? The only thing I can think of is if the 30 is due to the 60 L (60mins at 60lph) being left off as it is fuel for the destination aerodrome? But still Safe Endurance is based on flight fuel right, so I would have thought holding fuel was not counted?

Let me know

Thanks

Brook

FYI today is the day CASA change exam systems - lets hope they are up on Friday when I do the exam!!

For PNR calculations, you plan to return to the departure aerodrome. The departure aerodrome is the destination aerodrome.
In this instance, only the 30 minutes holding fuel needs to be considered.

Thanks Sydpilot! So the concept of Safe Endurance for a PNR does consider (as in subtract) holding fuel from the total fuel, but only the departure aerodrome, as any time BEFORE the PNR you can R(eturn whereas after flying past the PNR you would be obligated to consider the safe endurance differently.

Indeed. Holding fuel is just another reserve.
The PNR considers returning to the point of departure with all fuel reserves intact.
Think of it as point of safe return.

Awesome, thanks heaps sydpilot - its returning to point of departure with ALL fuel reserves intact. That's makes all the difference and now makes perfect sense. "All reserves intact", why didn't I think of that! Now it makes sense!

Yes, when you calculate a PNR you are simply finding the maximum distance you can fly away from your departure point in a particular direction and still return to your departure point with all required fuel reserves. As far as the calculation is concerned, the departure aerodrome is the destination and any OPRs applying to the departure aerodrome must be considered.

Remember also that a PNR is NOT an emergency. For example, imagine you departed Sydney for Lord Howe Island and an accident on the only runway at Lord Howe Island forced you to return to Sydney from your PNR. When you arrived back at Sydney, ATC would give you no priority whatsoever. You would be treated the same as any other arrival and, if Sydney required holding, it would be assumed that you allowed for that when you calculated the PNR.

As far as the PNR calculation is concerned, holding at the flight planned destination has nothing to do with it,

Bob

Thanks Bob! OPR's at departure aerodrome. Let me see, when did I last eat (or how full was my bladder) before leaving the departure aerodrome...

We need a new HPL section - a pilots bladder can hold x glasses of water. A pilot has a 250ml drink of water whilst on a break but forgets to go to the toilet before embarking on a trip 350 nm away at a TAS of 100kts.

Will the pilot

a) urinate in the bottle,
b) in the aircraft
c) in their pants
d) be able to contain themselves until they reach the destination...

Ha Ha - Good one Brook

I know some who gave ML a "diverting for human performance reasons" call once. He was holding over an airport waiting for some fog to burn off when he decide he just could wait any longer. You could hear the chuckle in the controllers voice.

Cheers,
Mister W