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Given:

Distance from departure to destination: 210 NM
Safe Endurance: 3.5 h True
Track: 310°
W/V: 270/30
TAS: 120 kt

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

  • A
    200 NM
  • B
    125 NM
  • C
    100 NM
  • D
    10 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 270º under the "TRUE HEADING" index at the top.
2. Set the center point on the True Airspeed (TAS) of 120 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: 130º
5. Note that this heading would result in 8ºL drift and a track of 122º.
6. Reduce the heading value under the index until the heading minus the drift gives a track of 130º. This occurs at a heading of 138º with 9ºL drift.
7. The groundspeed for this track is approximately 142 kt.
  • GS out: 310º

5. Note that this heading would result in 10ºR drift and a track of 320º.
6. Reduce the heading value under the index until the heading plus the drift gives a track of 310º. This occurs at a heading of 300º with 10ºR drift.
7. The groundspeed for this track is approximately 96 kt.


We can now apply the formulas:
Time (to PSR) = E x H / 0 + H
Time to PSR = 3.5 x 142 / 96 + 142 = 2.09 h

To find the distance from the departure airport to the PSR, we simply multiply the time to PSR by the GS OUT: 2.09 h × 96 kt ≈ 200 NM.

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