Given the following information, what is the ETA overhead the Point of Equal Time (PET) between positions A and B, if the aircraft was overhead A at 14:35 UTC?
Distance from A to B: 2 900 NM
True airspeed: 470 kt
Average wind component "out": +55 kt
Average wind component '"back": -75 kt
Safe endurance: 09:30
The Point of Equal Time (PET) allows a pilot to decide which is the quickest landing area to get to and is the position of a point on a track, where it is as quick to go on, as it is to turn back.
The formula to calculate the position of the PET is:
- Distance to PET = (D x H) / (O + H)
Where:
- D: Sector Distance
- O: Groundspeed Out
- H: Groundspeed Home
1. The Groundspeed Out (O) is: TAS + 55 kt = 525 kt.
2. The Groundspeed Home (H) is: TAS - 75 kt = 395 kt.
3. Thus, the Distance from A to PET is: (2 900 NM x 395 kt) / (525 kt + 395 kt) = 1 245 NM.
4. The Time from A to PET is given by the formula: Time to PET = Distance to PET / O = 1 245 NM / 525 kt = 2.37 hr or 02:22.
5. Therefore, the ETA overhead the Point of Equal Time (PET) will be: Time overhead A + Time to PET = 14:35 UTC + 02:22 = 16:57 UTC.
NOTES:
- To calculate the Time to PET, divide the distance to PET only with the Groundspeed Out (O), NOT the Groundspeed home (H), because the helicopter reaches PET flying outbound.
- The Safe Endurance must be ignored. It is given just to confuse you with the Point of Safe Return (PSR) formula.
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