Point of Equal Time (PET)

Point of Equal Time (or "Decision Point")

Is the point between two airports that are suitable for landing at which the time to fly on the the next airport is the same as the time required for a return to the previous one.

In zero wind conditions the PET lies exactly halfway between the two airports. However, in windy conditions the PET is displaced into the wind.

Formula:

PET = D x H / (O+H)

D = Distance between the two points
O = groundspeed out
H = groundspeed home

PET is a Distance calculation meaning that the answer will be in NM. If you were asked for the TIME to PET just use simple   "T=D/V" where speed (V) is ground speed Out.

Engine Failure PET

If the Question states an engine failure than the speeds used will be as follows;

GSo = 1 Engine Ground speed out
GSh = 1 Engine Ground speed home

Use both engine failure speeds in the PET formula. However, for the T=D/V we use the all engine GSo!

Find windcomponent to calculate GS

When a course is given together with the wind direction and speed, we first need to obtain the longitudinal wind component (headwind or tailwind) before we can convert TAS into GS.

Method 1 (quick formula): Windspeed x Cos(wind direction - true course)

Method 2 (navigation computer):

- Put course on top, turn wind scale to the wind direction
- Shift so that the line of the TAS intersects with wind speed
- Ground speed for that leg (OUT) can be read inside the circle
- Do the same but now with the opposite course to find the GS for the opposite leg (HOME)

Questions on Point of Equal Time