Wardair Canada From Canada, joined Dec 2000, 28 posts, RR: 0
Reply 1, posted (14 years 2 months 1 week 2 days 21 hours ago) and read 2826 times:
First of all, if you take into account the winds aloft... a routing from LAX-SYD takes you across the equator at some point near the Hawaiian Islands, in the Northern Hemisphere the winds blow from West to East and in the Southern Hemisphere, the winds blow from East to West.
So a 744 can fly LAX-SYD non-stop simply because it does not face a headwind the entire flight, it faces a headwind in the first half of the flight and in the second half of the flight, it has a tailwind. So these two even out.
A routing from JFK-SEL is different because you are flying against the wind the entire flight so that has a considerable effect on range and fuel consumption because the plane has to work harder to push itself against the headwind. Also due to the way flight routes are planned now, you must avoid Russia so that means you have to fly around instead of straight on. That adds to the flight time and you have to take even more fuel and less passenger loads to compensate for the range shortfall. However it is possible to fly from SEL-JFK non-stop with a full load of passenger depending on the winds aloft.
However things will change soon, with the upcoming possibility of true polar routes which offer flights the most direct route from North America to Asia, thus shaving off an hour or so off the flight time, you will see more non-stop flights being made.
Its all a matter of how direct the route is, what kind of winds aloft and the ability to carry enough fuel to make the trip.
Some airlines do not carry a full load of passengers because that would mean they have to carry less fuel to remain within the allowable takeoff weights. So a 744 operator may carry 250 instead of 400 passengers and a full load of fuel and they'll make it non-stop. Some elect to carry a full load and make a fuel stop in Anchourage, Alaska.
B747skipper From , joined Dec 1969, posts, RR:
Reply 2, posted (14 years 2 months 1 week 1 day 8 hours ago) and read 2788 times:
JFK-SEL route is against the jet stream - on the North Pacific routes from Japan to Alaska/Canada I have encountered westerly winds of 150 kts often.
Two corrections to make: In the Southern hemisphere the jet stream is SAME direction, from West to East (located generally So. Australia to New Zealand to Southern Chile/Argentina)... A few things are different in the Southern hemisphere, but not the West to East flow -
Second correction avoiding Russia - no longer is necessary, numerous flights operate into or through Russian airspace. They love the overflight fees, and selling fuel to landing planes... things have changed...
OPNLguy From , joined Dec 1969, posts, RR:
Reply 3, posted (14 years 2 months 1 week 1 day 6 hours ago) and read 2772 times:
The other 2 gents have mentioned the winds, and they are a big player--especially on such a long flight...
As you mentioned being a newbie, it might help to to think about the effect of the winds in this way...
Imagine you're at an airport (or other place) that has one of those moving sidewalks, from point-A to point-B, but that it's busted. As you walk along from A-B, you're progressing at a certain speed, with nothing helping nor hindering you. An aircraft flying in similar "still" air (no headwind or tailwind) calls this "true airspeed."
OK, now you're walking that same moving sidewalk from A to B, and it's now working, also moving the same direction A to B. Your feet are still walking the surface of the moving sidewalk at the same speed as they were when the moving sidewalk was busted, but now you have the additional speed of the sidewalk itself moving from A to B. As you look left/right at things that are *not* on the moving sidewalk, you'll see thing going by pretty fast.
Finally, let's assume you're at B wanting to go back to A, but the moving sidewalk is still running in the direction of A to B. As you walk back towards B, your speed on the sidewalk itself will be the same as before, but your overall progress back to A will be slower, since you're "fighting" the A-B movement on your B-A trip. You'll notive things on the side going by much slower.
The effect on a long aircraft trip can be a big one, as mentioned. For example:
Assume a 5000nm trip, a true airspeed of 450 knots, and 100 knots of headwind (or tailwind).
100 Headwind (minus)
350 Groundspeed (GS)
14:17 Time enroute (Distance divided by GS)
000 Wind (Still air)
11:07 Time enroute
100 Tailwind (plus)
09:06 Time enroute
As you can see, the difference is about 5:00 of flight time, and if the aircraft burns fuel at the rough rate of 10,000 pounds per hour, that's a difference of 50,000 pounds of fuel, which may mean that 50,000 pounds of payload (people, baggage, freight, etc.) does't make the flight that has to contend with these kinds of headwinds.
One of the things we (dispatchers) do is to determine flight plan routings that avoid/minimize headwinds, while seeking favorable tailwinds.
Sorry for the length, but I hope this sheds lends some context to the effects of the winds..