Halfway to Hawaii?

Well, the first problem is that the winds going from the west coast to Hawaii are not always consistent across the entire route. It has been several years since I've done that trip, but I recall often seeing much weaker tailwinds at the beginning of the flight than at the end.

I assume they are asking about the time to the halfway point in miles, as opposed to the halfway point in time (they are not necessarily the same thing).

Just looking at the winds today, it looks like you would have slight tailwinds across Texas and New Mexico, turning into a crosswind in California, and a headwind as you head out across the pacific.

You can get the wind charts here:

WAFS Winds/Temperatures Facsimile (T4) Charts

(Scroll down to the "N America and Pacific Plot" and click on that).

The numbers represent temperatures-- not that important for your purposes, and the little hash marks are like the feathers on an arrow-- the more of them there are, the stronger the winds are.
Image Unavailable, Please Login

 

What i think you are looking to calculate is an Equal Time Point (ETP) and I'm assuming they are doing it with just basic information rather than more accurate wind information across the route. Normally you would have more info but I will kinda guess at what the numbers should be.... Will do some calculations and post it up in a bit based on best guesses.

 

ETP is different. The ETP is where the time is the same to continue or return.

If you are flying into a strong headwind, the ETP will be considerably further than halfway, even in terms of flying time (and especially in distance).

He is either looking for the halfway point in terms of time, or the halfway point in terms of distance. Neither is the same as the ETP unless there are no winds for the entire trip.

 

Yeah.... I was thinking that maybe they just used an ETP and called it "halfway" because pax wouldn't know what an ETP is. If anybody is interested I can put up a sample ETP problem.

As for the basic math of it I get 3+36.5 (0857.5 clock time) on the most basic look at the problem. Green mark on whiz wheel shows where I see the time. Really doesn't take into account the climb out performance and winds which is where I suspect the real problem is. What you would really need to do, in my estimation, is to find out what a typical climb profile is to whatever flight level is typical. Once you subtract that ground distance from the overall you can have a lot better chance at calculating where/when you will be halfway at cruise.
Image Unavailable, Please Login

 

Probably 5/8 of the distance is covered half way through the flight based on climb to altitude and speed increase as fuel burns off.

 

I dunno if he commercial guys do it differently but they should be flying what they filed for. Going faster than the controllers expect will get the controllers a bit upset, particularly if you are in RVSM airspace.

 

I'd just cheat and run Foreflight from my iPad on this contest

 

First thing to ask is whether the miles figures given were in statute miles (5280') or nautical miles (6076.1'). Ground speed of 488 knots is 561.6 mph. Actually makes no difference.

Assuming everything was in the same units 1752/488 is 3.59 hours or 3 hours 35 minutes 24 seconds. Take-off, climb-out, descent, and landing considerations are beyond the scope of what a passenger would know. Clearly wrong because it assumes you overfly your destination and departure sites at 488 kts gs.

Doing it the simple way 1307 less 0521 is 7 hrs 46 minutes total flight time. Half of that is 3 hrs 52 minutes, with take-off and landing already in the mix. All the other stuff is just to confuse you.

 

If it was me, and the winds are more or less as they are today, I'd figure it the simple way and subtract 15 minutes.

 

Why subtract 15 minutes? I would think you would want to add some time. I would say calculate the first 50 miles at 250 knots just to reflect the lower speeds during departure and climb out then calculate the remaining portion to the halfway point at whatever the cruising ground speed might be. That's the most basic explanation of how I would do it if having to plan an oceanic crossing by hand.

 

Halfway to Hawaii

Google it and win......

 

On a trip of that length, time spent climbing out is meaningless.

You subtract because (at least today), you'll have tailwinds for the first 40% or so of the flight. Then headwinds. Since you are only figuring the time for the first 50%, those tailwinds will have a significant effect on the first half time, even though the entire trip will end up being roughly affected by the average wind component.

As for 15 minutes, it's just a guess. Use 10 if you prefer, or 20...

 

That could be true in the airline world. My experience has almost entirely been in older systems and the way we calculate cruise times overwater is tied to the legacy fuel planning procedures.