Given:
Distance from departure to destination: 220 NM
True track: 175°
W/V: 220/10
TAS: 135 kt
What is the distance of the PET from the departure point?
Refer to figure.
Solving from Heading (HDG) & Ground Speed (GS), knowing WV, TAS and required track.
1. Set wind direction to 220º under the "TRUE HEADING" index at the top.
2. Set the center point on the True Airspeed (TAS) of 135 kt.
3. Mark the wind velocity 10 kt down from the centre point.
4. Initially, set the True Track under the "TRUE HEADING" index.
- GS home: 355º
6. Reduce the heading value under the index until the heading plus the drift gives a track of 355º. This occurs at a heading of 352º with 3ºR drift.
7. The groundspeed for this track is approximately 142 kt.
- GS out: 175º
5. Note that this heading would result in 3ºL drift and a track of 172º.
6. Reduce the heading value under the index until the heading minus the drift gives a track of 175º. This occurs at a heading of 178º with 3ºL drift.
7. The groundspeed for this track is approximately 128 kt.
We can now apply the formulas:
Distance to PET = (GS home x Distance) / (GS out + GS home)
Distance to PET = (142 x 220) / (128 + 142)
Distance to PET = 116 NM
Time to PET = Distance to PET / GS out
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