Aviation Calcs

PNR & ETP

Point of No Return and Equal Time Point Calculator

The two classical decision points on a long leg. The point of no return (PNR) is the farthest you can fly toward a destination and still get home within a stated safe endurance. The equal-time point (ETP, or critical point) between A and B is where it takes as long to go back to A as to go on to B. Enter outbound and homebound groundspeeds, or a TAS and a wind component.

Problem
Speeds as

Positive is a tailwind outbound (and a headwind coming home). Negative is a headwind outbound, as in the 30 kt headwind example.

Distance

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Point of no return

With outbound groundspeed O, homebound groundspeed H, and a safe endurance E (hours), the distance to the PNR and the time to fly out to it are

dPNR = E × O × H / (O + H),   tout = E × H / (O + H)

Worked example: TAS 150 kt, 30 kt headwind outbound (so O = 120, H = 180), endurance 5 hours. The PNR is 360 NM, at 3 hours outbound — you can fly longer outbound than homebound because the return is a tailwind. In still air the PNR is halfway in time (and halfway in distance).

Equal-time point

Between airports a distance D apart, the ETP measured from A is

dETP = D × H / (O + H)

Time from the ETP back to A equals time from the ETP on to B. With the same 120 / 180 kt groundspeeds and a 600 NM trip, the ETP is 360 NM from A: two hours either way.

Sources

Classical PNR / ETP (critical-point) identities used in long-range flight planning; FAA Pilot’s Handbook of Aeronautical Knowledge (flight planning, wind). This is not a substitute for the fuel-reserve rules in 14 CFR 91.151, 91.167, or the corresponding Part 121 / 135 requirements. For trip fuel itself, see the fuel planner.

Frequently asked questions

Is the PNR the same as the ETP?

No. The PNR depends on how much endurance (fuel time) you have and is the last point from which you can still return to the departure point. The ETP is a point between two airports at which the time to go either way is equal; it does not, by itself, say whether you have the fuel to do so.

What wind component should I use?

The component along the route: tailwind outbound is positive on this page. A crosswind that only reduces TAS equally both ways can be folded into a lower TAS; a wind that is along-track must be entered as a component or as two groundspeeds.

Does this include a fuel reserve?

Only if you put the reserve into the endurance you enter. For a legal reserve, compute the required fuel separately (the fuel planner on this site implements the Part 91 VFR and IFR memory items) and use the remaining safe endurance here.