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Point of equal time formula

How to Calculate Distance and Time to the Point of Equal Time and How to Calculate Time and Distance to the Point of Safe Return

Calculating distance and time to the point of equal time (PET)

The point of equal time (PET) is a location along your route of flight where the time it would take you to reach your destination would be exactly the same amount of time to turn around and fly home. It varies depending on the wind which affects your groundspeed. The following formulas will tell you where it is and how long it will take you to arrive there.

Distance to the point of equal time (DPET)

To calculate DISTANCE to the point of equal time (DPET) you need:

  1. the total distance from your point of origin to your destination (D)
  2. your ground speed home (GSH)
  3. your groundspeed out (GSO)

Example

  1. 560 NM (D)
  2. 180 KTS (GSH)
  3. 220 KTS (GSO)

DPET = (D x GSH) / (GSH + GSO)
DPET = (560 x 180) / (180 + 220)
DPET = 252 NM from your point of origin

Time to the point of equal time (TPET)

To calculate TIME to the point of equal time (TPET) you need:

  1. distance to point of equal time (DPET)
  2. your groundspeed out (GSO)

Example

  1. 252 NM
  2. 180 KTS

TPET = DPET / GSO
TPET = 252 / 220
TPET = 1 hour 24 minutes from your point of origin (1.4)

Calculating Time and Distance to Point of Safe Return (PSR)

The point of safe return (PSR) is a location along your route of flight where you could still return back to your point of origin based on your endurance. The following formulas will tell you how long it will take to reach the PSR and and the distance to it.

Time to Point of Safe Return (TPSR)

To calculate TIME to the point of safe return you need:

  1. your endurance (E)
  2. your ground speed home (GSH)
  3. your groundspeed out (GSO)

Example

  1. 5 hours
  2. 180 KTS
  3. 220 KTS

TPSR = (E x GSH) / (GSH + GSO)
TPSR = (5 x 180) / (180 + 220)
TPSR = 2 hours 15 minutes from your point of origin (2.25)

Distance to Point of Safe Return (DPSR)

To calculate DISTANCE to the point of safe return you need:

  1. time to point of safe return (TPSR)
  2. your groundspeed out (GSO)

Example

  1. 2.25 hours
  2. 220 KTS

DPSR = TPSR x GSO
DPSR = 2.25 x 220
DPSR = 495 NM

2022-06-22T14:05:15-04:00

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