BoulderHyattHopper

I have to say I think I am more confused than I was when I started the post. But I leave in 20 hours and at this point, don't care much except for 4 straight days of getting fried at the Hyatt pool... AHHH, heaven!

Of course, a few drinks on the plane and I might not even have to make it to Kauai to get blitzed...

Counsellor

BoulderHyattHopper - Try this:

When I was in high school (which was shortly after they invented dirt), there was a typical math word problem somewhat as follows: A powered boat goes at a rate of "S" miles per hour in still water. How far does it travel (i.e., what is the net speed) if going upstream or downstream when the current is "C" miles per hour?

The answer was, if going downstream, add the current to the speed ("S"+"C" mph); if going upstream subtract the current from the speed ("S"-"C" mph).

You can use that concept to make a simple formula for the problem:

1. Take the speed of the plane (in miles per hour), subtract the headwind (in miles per hour) and you have the number of miles the plane actually travels in an hour.

2. Divide the total miles to Hawaii by that number. This gives you the number of hours it will take to get to Hawaii.

3. Divide that number by 2. This gives you the number of hours it takes to get half-way to Hawaii.

4. Convert that number (which will be a decimal) into hours/minutes/seconds.

5. Add the resulting number to the time of take-off.

And there you have the answer (if they're asking what time it will be at the take-off point when you pass the "half-way to Hawaii" point, which is what they used to ask).

I've used this formula on the "half-way to Hawaii" with reasonable success.

The formula is simple, but also simplistic. It does not take into consideration that the headwind or tailwind is not blowing along the axis of flight (i.e., you're not flying directly into the wind, or directly in front of the wind), and thus shouldn't be adding or subtracting the whole speed of the wind (rather the wind causes a vector; if you want to figure it out, make a triangle with one leg being the speed of the plane, another being the speed of the wind, and the angle between them being the angle at which the wind is blowing on the plane; since "side-angle-side" determines a unique triangle, the third leg of the triangle becomes the distance covered per unit of time). It also doesn't take into consideration variations in speed of the wind, or of the plane as it becomes lighter through consumption of fuel. And there are a lot of other factors that it doesn’t take into consideration, including Glen’s Champagne.

But then again, that would take all the fun out of it.

(Edited to add more explanation.)

[This message has been edited by Counsellor (edited 09-26-2002).]

l etoile

Based on my husband's experience flying in the cockpit, the figures you're given seldom relate to the actual flight. Often, the FO (or used too be FE) just makes up some figures (and figures out the answer). It is a very simple calculation, but it seldom is an indicator of your actual midway point.

Back in 1974 I traveled to Hawaii for the first time with my parents and have fond memories of father winning. Back then first prize was tickets to Sea Life Park and second was champagne. I usually manage to get a bottle of champagne now.

Mark Rogers

I don't know about how it used to be, but it's very easy to determine a midpoint on the airplanes today, as well as provide the information given to the passengers.

All of the information read by the crew comes directly off the flight plan This includes heading, altitude, ground speed, true airspeed, and wind direction/velocity (I'm not certain if all that is given, but it's all on the flight plan). It's also very easy to construct a waypoint that is midway (based on distance) along the course. The crew would only need to note the second at which the waypoint is crossed, since the FMS would already record the hour and minute.

TimCLE

My Garmin eTrex works well onboard and I've never been questioned about it. Add your departure point and HNL to the waypoint database, divide the distance by two...

l etoile

Mark Rogers: I was rushing off and didn't give as complete a posting as I should have. In my husband's experience, the FOs have made up the figures when winds are very calm and they figure it would be too easy for passengers to come up with the correct answer so they make up some wind speeds. Also, you usually need to provide your answer within 1/100th of a second (at least that's what I always do). I think you end up with way to many winners if it's only to the closest second. At that, one flight I had recently they gave out six bottles. Of course, on another recent one they didn't play at all.

As for the GPS people, FAs have sometimes popped their head into the cockpit to tell the pilots that a passenger is using a GPS and ask if it's OK. Pilots, from what my husband has observed, have always said no problem. I've never noticed that those folks have won.



[This message has been edited by letiole (edited 09-25-2002).]

LIH Prem

Have we all forgotten why "halfway to Hawaii" is so important to the flight crew?

Think about it.

-David

Law Lord

Tying together the ideas on windspeed and in particular the comment of DHAST on the accuracy being controlled by the least precise measurement, let's assume (1) that the pilot can determine to within a second or two when the airplane actually passes through the halfway point, and (2) the stated windspeed is accurate to within only about 5 knots.

To simplify the math, assume that the flight path is 2500 nm long and the plane's airspeed is exactly 500 kt. With no wind the flight takes exactly 5 hours. (I'm ignoring climb and descent, obviously.)

A 5kt headwind adds 3 min 1.8 sec to the trip. A 5kt tailwind subtracts 2 min 58.2 sec from the trip. So the margin of error accounts for a 6 min difference in the trip, or a 3 min difference to the halfway point.

Based on this, I hypothesize that to guess the halfway point to within 5 minutes or so represents skill. To guess to within 5 seconds is the same skill, plus a lot of luck.

PremEx

Amateurs!

I just keep looking out the window and mark the time down when we cross that big red line down on the water that marks the half way point.

TropicalFlyer

On my last flight home this past Sunday, the instructions from the pilot included a new item: "Please do not use a GPS since it would be cheating."

TF

Mark Rogers

Well, I haven't. On the way to Milan last week, we also played the "halfway between Gander and Glasgow" game, and on the way back it was the "Which is closer - Shannon, Rekjavik, or Gander?" game. We just don't ask the passengers to play along...

ozstamps

PLEEEZE do not ask the passengers to join in Mark Rogers. Bad look for the flight deck to be asking THOSE kind of questions.

Reminds me of that wonderful and legendary story of the guy thumping the desk DEMANDING he get upgraded. Says to gate agent: "do you KNOW who I am" to which she responds by getting on PA and says "Ladies and gentlemen there is a passenger here does not know who he is - can someone please assist him". To loud applause from all nearby.

Law Lord

The story told by ozstamps is similar to an old chestnut passed down from class to class at my college.

The students in the final examination were writing furiously in their bluebooks when the test's proctor called "time" and directed everyone to bring their bluebooks to the front of the room. All but one of the students complied. One kept writing.

When the proctor noticed, he told the student to turn his book in, and it would be marked "late" so that the professor would know that the student had extra time to answer. The student came forward, indignantly saying, "This is outrageous! Do you know who I am?" The proctor, cowed, hesitantly said, "No, I don't."

The student gleefully cried, "Good!" as he thrust his bluebook into the middle of the pile and jumbled the others around it, then ran off.

wingless

Labor Day weekend I turned in my Halfway to Hawaii card and my companions. I wrote down his answer and mine with some simple calculations and I got second place.

Normally, they do not have second place but the purser was so impressed because I was off -55 seconds on one card and I was off +55 seconds on the other. He announced that their was a tie for second place...and it was us.

BoulderHyattHopper

I WON!!!

I was off 3 seconds!!!

8:55.06 and I guessed 8:55.03

Mr. BHH guessed 8:55.48 and didn't get 1st, 2nd or 3rd!