Physics 101. Here we go...

Let D be the distance traveled in time "t", V be the plane cruising speed, and +/-w be the wind velocity (can be positive or negative depending on whether it is tail to front or front to tail, respectively). The distance the plane will travel after a time t at speed V, against or with a wind velocity of w will be:

Code:

D = V*t + w*t = t * (V+w) with the wind
or
D = V*t - w*t = t * (V-w) against the wind

The pilot will give you the distance (D) between LAX/SFO and HNL, the plane cruising speed (V), the wind velocity and direction (+/-w) and the exact clock time (T) when the plane left LAX or SFO.

Code:

In the case of tail wind, with D/2 being halfway distance to HNL, you get
D/2 = t * (V+w)
or wind in the opposite direction:
D/2 = t * (V-w)

Now all that remains is for you to solve either equation for for "t"

and then convert "t" to clock time (T") and add it to the departure time (T).

Code:

Halfway time to HNL = T+T"

That will get you very very close but you may need to make an educated guess about small adjustments to make, e.g., if you think of something that might have slowed and sped up things a bit (this assumes you were paying attention).

I hit the Halfway time to HNL from LAX within 2 seconds last April!

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