Point of no return and point of safe return

Navigation · Chapter 19 · DGCA CPL and ATPL

How far you can fly out and still get home on the fuel you may use, with the wind, a change of fuel, or different fuel flows.

Remember

Safe endurance = (fuel − reserve) ÷ flow; never total endurance.
PNR: d = E × O × H ÷ (O + H); t = E × H ÷ (O + H) = d ÷ O.
Find O and H on the CX-3 (Wind Correction), out track and its reciprocal.
Nil wind gives the farthest PNR; any wind brings it closer. Radius of action = distance to the PNR.
More fuel → PNR further out, in proportion. Different fuel flows: d = usable fuel ÷ (kg/NM out + kg/NM home).

What is the point of no return?

How far can you go and still come back?

The problem • You fly out over the ocean from base A • The destination may close (weather), and there is nowhere else to land • So you must know: how far can I go and still get back to A?
The fuel tank • Gold: fuel you may use. Its time is the safe endurance: here 4 h • Red: the reserve, kept for holding and landing at the end • You never plan to fly on the reserve
Out and back • Fly out, turn round, fly home • Turn at the right place and you land with the reserve untouched • That farthest turn-back point is the PNR, the point of no return, also called the point of safe return (PSR)
Turn back too late • Fly on past the PNR, then turn back • The gold fuel runs out on the way home: you land on the reserve • Not allowed: past the PNR you are committed to go on
Out is slower here • A headwind going out: GS out O = 200, GS home H = 250 • So the way out takes longer than the way home: 2 h 13 out, 1 h 47 home • The two times add up to the safe endurance, 4 h
Where the formula comes from • Time out t, time home E − t; the distance is the same both ways: t × O = (E − t) × H • So t = {{E × H // O + H}}, and the distance is t × O: • d = {{E × O × H // O + H}}
CP and PNR side by side • CP (gold): which way is quicker from here. Needs only distance and speeds • PNR (magenta): how far you can go and still get back. Needs the fuel • Same route, same wind, two different points
Radius of action • Draw that distance round the base: the radius of action • Anywhere inside the ring, you can go and still get back

Solve it: time and distance to the PNR

Solve it: PNR

Solve it: time and distance to the PNR