Point of Safe Return (PSR) — Page 264, Lesson 263

I want to walk you through the Point of Safe Return, or PSR. This is a critical concept for flights where, if things go wrong at your destination, your only safe option is to turn around and go back to where you started. Let’s start with the definition. The Point of Safe Return (PSR) — which used to be called the Point of No Return (PNR) — is the furthest point along your planned route to which you can fly and still make it back to your departure airfield, or your departure alternate, within the aircraft’s Safe Endurance. Now, what exactly is Safe Endurance? It’s the length of time — or the amount of fuel — that an aircraft can fly without consuming the mandatory fuel reserves that must be available overhead the departure airfield or departure alternate, in case you have to return from the PSR. In other words, Safe Endurance is the total time you have available for the outbound leg and the return leg combined, while still keeping your legal reserve fuel untouched when you get back overhead the departure point. This is a period of time, and it’s what we use to calculate the PSR. It is very important not to confuse Safe Endurance with Total Endurance. Total Endurance is the total time an aircraft can stay airborne until the tanks are completely empty. Safe Endurance is shorter — it stops when you still have your mandatory reserves left. So when would you actually need to calculate a PSR? If the weather, runway condition, let-down aids, or the political situation at your destination is likely to get worse, and your only option would be to turn back to the departure airfield or departure alternate, then it’s prudent to calculate a PSR. Normally, you’d only need this for flights to what the book calls an “isolated destination where no adequate destination alternate exists.” Examples given include flights from mainland airfields to places like Easter Island, Cocos Island, Tahiti, Ascension Island, and the Azores. Here’s how you use it in flight. At a reasonable time before your estimated time of arrival at the PSR, the pilot checks that the destination airfield’s weather, landing aids, and runway state are acceptable — typically for a period from one hour before to one hour after the destination ETA. Now, let’s look at the geometry. The distance out to the PSR equals the distance home from the PSR — it’s the same physical point on the route. In zero wind, the time out to the PSR and the time home from the PSR will be equal. But if there’s an overall wind component, the time out and time home will be different. However, in every case, the sum of those two times — out plus home — equals the Safe Endurance time. That figure shows the concept visually: the aircraft departs, flies out to the PSR, and then returns, with the total time for both legs matching the Safe Endurance. Next, we’ll look at how to actually derive the formula for calculating the PSR.