Point of Safe Return (PSR) Calculator
PNR's stricter sibling: the last point from which returning lands you home WITH full reserves — including the holding/approach allowance the bare formula skips.
PNR with the lawyer's edits: reserves and an approach allowance subtracted BEFORE the formula, so crossing the PSR means a normal landing back home is no longer guaranteed — not that the tanks run dry. Brief the conservative line.
Formula
⚠️ For flight planning and education only — verify with your POH/AFM and official sources. Not for primary navigation or in-flight emergency decision-making without POH data.
PNR's stricter sibling: the last point from which returning lands you home WITH full reserves — including the holding/approach allowance the bare formula skips.
About Point of Safe Return (PSR) Calculator
The textbook PNR lands you home with dry tanks — a definition only useful to accident investigators. Operational planning briefs the Point of Safe Return instead: the same harmonic-mean geometry computed on the fuel that remains after your landing reserve and an approach allowance are locked away. This calculator does the subtraction first and the formula second, so the line it draws means 'past here, returning with normal margins stops being guaranteed' — the line a prudent brief actually wants.
How to use Point of Safe Return (PSR) Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula PSR = (usable − reserve − approach)/flow × harmonic of the two ground speeds substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Point of Safe Return (PSR) Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula PSR = (usable − reserve − approach)/flow × harmonic of the two ground speeds with sources cited on the page
- ✓PNR with the lawyer's edits: reserves and an approach allowance subtracted BEFORE the formula, so crossing the PSR means a normal landing back home is no longer guaranteed — not that the tanks run dry. Brief the conservative line.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
PSR vs PNR — is the difference just vocabulary?+
It's the fuel state on arrival: PNR's classical definition spends ALL endurance, arriving empty; PSR protects reserve + approach fuel, arriving normal. The formulas are identical — only the endurance fed in differs. Commonwealth training says PSR, American texts often say PNR-with-reserves; what matters is knowing which your number means before trusting it.
Why add an approach allowance on top of the reserve?+
Because the return ending matters: arriving overhead home base still requires descent, possibly an instrument approach or a circuit behind traffic — fuel the en-route reserve isn't meant to fund. A 1–3 gallon (or 10–15 minute) approach allowance keeps the reserve intact through the landing, which is the entire point of having one.
When does the PSR govern a real decision?+
Destination-uncertainty flights: the island with one runway and fickle fog, the bush strip with unknown surface condition after rain, the airshow arrival that might be closed. The brief is 'if we haven't confirmed the destination by [PSR time/place], we turn around.' It converts en-route anxiety into one pre-made decision with a place on the map.
How do changing winds en route affect a briefed PSR?+
They move it — the formula's two ground speeds are forecasts. The robust practice: recompute with measured wind at the first cruise checkpoint (our in-flight wind tool measures it), and treat a stronger-than-forecast outbound tailwind as the dangerous case (it flatters progress while quietly hauling the PSR closer). A PSR that only gets re-checked when things look bad has failed its job.
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