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Point of no return (PNR) 2

Given position fix prior to alternate airport

There are times when a position fix is given that is NOT overhead the airport you plan to return to. The classic scenario is where you have not yet arrived overhead the alternate when given the bad news about the destination airport. An example being:


Tracking from Alice Springs to Darwin (S12 25’/E130 54’) via Tindal VOR. When 150 nm before Tindal at 1100 UTC you are advised that Darwin needs an alternate, and that Tindal is suitable for this purpose.

Data at 1100 UTC: Ops normal/TAS 260 kt/FL180/Wind 270M50 kt/Safe endurance (excluding reserves)100 min.

Track/distance from 1100 UTC fix to Tindal is 347M/150 nm.

Track/distance from Tindal to Darwin is 321M/152 nm.

1 Inop TAS 170 kt/FL110/Forecast wind 260M30 kt.

Which of the answers best represents the planned ETA at the 1 Inop PNR for Tindal ?

a. 1200 UTC b. 1155 UTC c. 1205 UTC

First you must get the estimated “safe endurance” when you arrive overhead the airfield you intend returning to (ie: Tindal in this case). Then apply formula.


Applying the PNR using the endurance of 64 minutes when overhead Tindal we get an ETI out to the PNR 1 Inop of 28.6 minutes.

So ETA at the PNR is 28.6 minutes after the overhead Tindal position

= 1204.6 UTC. Answer “C” best !

If we wanted instead to find the distance from Tindal to the 1 Inop PNR we would apply the Normal ops GS OUT of 228 kt to the time out of 28.6 minutes to get a distance of 108 nm.

Note that the time out from Tindal to the PNR at normal operations groundspeed, plus the time home from the PNR 1 engine inoperative at 1 engine inoperative groundspeed, must equal the total safe fuel endurance when overhead Tindal, when on your way out to the PNR.

Be aware that the track change overhead Tindal may significantly alter your groundspeeds in the Tindal to Darwin sector compared to those on the Alice Springs to Tindal sector.

The above is an extract from the Internet delivered ATPL Navigation course, and I trust you found it beneficial. For information on ATPL courses delivered by the Internet or by books, refer to these web pages:



Best regards

Rob Avery


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Marty says ... "Goodbye to GA".

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