How do we calculate Endurance (E) for calculating PNR?

[yasirabbasmalik]

i have a little trouble here finding out the value of Endurance in PNR formula? what is it based on? URGENT REQUIRED THANKS!

[BOAC]

Simplest way is to use (fuel on board LESS Final Reserve)/Fuel Consumption at cruise level. If it is a PNR for you with a 'panic' factor built in:) I would also take off an extra bit for holding/approach etc.

[Tinstaafl]

Endurance is the fuel available to be used for flight enroute from place to place and excludes all other fuel required to be there for other purposes eg holding, final reserve, fixed reserve, variable reserve (VR), alternates, approaches and the like.

Start with total fuel on board, subtract all the fixed amounts such as final reserve, fixed reserve, holding (if required at the landing point) and alternate fuel if an alternate is required for the intended landing point and any other fixed amounts that the company operations manual or local rules require. This leaves an amount of fuel available to be used for flight from A-->B (or A-->A in this case) + any VR the rules might specify. If the VR required is 10% of flight fuel then this remaining fuel must be 110%** of flight fuel. Divide the quantity by 110% to find flight fuel.

Divide flight fuel by fuel consumption to find endurance.


**Don't make the mistake of thinking that flight fuel is 90% of this fuel. Imagine you have 100kg (litres/gallons/gills/whatever) of fuel and a requirement for a 10% VR. If you take 90% of this fuel (90kg for the hard of thinking or alcohol/exam study synergy believer) and call it flight fuel then the VR required will be 9kg, giving you 99kg to use. What about the remaing 1kg? It's there but not accounted for because 90% of a total is not the same as taking an amount and adding an extra 10% to find the total. So, the correct way in this example is to divide the total by 110%, not multiply it by 90%.

[Der absolute Hammer]

I think I remember that the fuel which determined endurance and which had to be expresssed in the same untis as groudnspeed out and groundspeed home for the equation solving was the cruise fuel required from top of climb to top of descent?

[411A]

For many years, with 4-engine piston, turbopropellor, and transport jet operations, the PNR was calculated thusly...


Time to PNR = E x H / O + H

O = ground speed out
H = ground speed home
E = endurance

Endurance was the total fuel on board (in hours) at the normal cruising fuel consumption, minus 1.5 hours reserve (or, 2 hours, if using island reserve).

Worked very well in service.:)

I never ever departed with less fuel than indicated above, and never had any arguments from management, either.

[Tinstaafl]

Australia's CPL exams require solving on-track PNR & CP (Equitime Point, if you prefer) using the formula. Senior Commercial Pilot Licence/Airline Transport Pilot Licence exams required us to calculate *off* track PNRs & Critical Points so plotting solutions became the order of the day.

At SCPL/ATPL level all fuel burns were sectorised, so a single fuel flow wasn't acceptable. Oz also requires a VR in the fuel allowance at CPL & ATPL level.