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Given:

Distance from departure to destination: 260 NM
Safe Endurance: 4.1 h
True Track: 150
W/V: 100/30
TAS: 110 kt

What is the distance of the PSR from the departure point?

  • A
    107 NM
  • B
    213 NM
  • C
    154 NM
  • D
    47 NM

Refer to figure.
The Point of Safe Return (PSR) is the last point on a route at which it is possible to return to the departure airfield arriving back with the required fuel reserves still available in the tanks. If the pilot chooses to continue past the PSR, he is now committed to landing at your destination.

Time (to PSR) = E x H / 0 + H

  • Where, E = Safe endurance based on available fuel; H = Ground speed home; 0 = Ground speed out

Solving from Heading (HDG) & Ground Speed (GS), knowing WV, TAS and required track.

1. Set wind direction to 100º under the "TRUE HEADING" index at the top.
2. Set the center point on the True Airspeed (TAS) of 110 kt.
3. Mark the wind velocity 30 kt down from the centre point.
4. Initially, set the True Track under the "TRUE HEADING" index.

  • GS home: 330º
5. Note that this heading would result in 10ºL drift and a track of 320º.
6. Reduce the heading value under the index until the heading minus the drift gives a track of 330º. This occurs at a heading of 340º with 12ºL drift.
7. The groundspeed for this track is approximately 127 kt.
  • GS out: 150º
5. Note that this heading would result in 14ºR drift and a track of 164º.
6. Reduce the heading value under the index until the heading plus the drift gives a track of 150º. This occurs at a heading of 136º with 11ºR drift.
7. The groundspeed for this track is approximately 88 kt.
We can now apply the formulas:
Time (to PSR) = E x H / 0 + H
Time to PSR = 4.1 x 127 / 88 + 127 = 2.422 h

To find the distance from the departure airport to the PSR, we simply multiply the time to PSR by the GS OUT: 2.422 hrs × 88 kts = 213 NM.

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