Question About Routing On Jfk-nrt Flights

[GadgetFreak]

Well, a rather diffferent topic than most, but I was hoping to hear from some pilots or others in the know on this. I came over to Tokyo yesterday on UA801 which was JFK-NRT. I have taken this flight a lot over the years, 3 times already this year and about 8 times in the last year and a half. I always enjoy watching the Airshow and have a pretty good idea of the flight path we take. Last time I took it, late February we were very far south. In fact we were down near Anchorage and were south of Mt. McKinley (got a great view). Normally we are somewhere north of Fairbanks though. The farthest north I have been was near the north slope of Alaska. But this time, the departure on Friday March 26th, we took a polar route. We went up the east side of Hudson Bay, over Baffen Island and then towards the pole. We were within 300 miles of the north pole according to the pilots announcement. We then went into Siberia and went South-east coming pretty close to Mongolia and out towards Japan. Question I have, of course, is how come? In general why would we take such a route? Who decides? Does anyone know why on this particular day we might have gone that way? Any input would be appreciated. Thanks.

 

[mweiss]

The jetstream plays a big role in the routing of flights. When heading westbound, it is typically better to avoid it; when heading east it is typically better to be in it. Saves fuel and time both ways.

Beyond that, it could be to avoid bad weather.

I don't know what was special about yesterday's weather, though.

 

[Bear96]

As mweiss alluded to, because of the jet stream, which generally stays well south of the pole, JFK -> NRT will typically fly much closer to the pole to avoid the jetstream and strong headwind, while NRT -> JFK will generally be much farther south to take advantage of the strong tailwind. You really see this to some extent with all North Atlantic and North Pacific crossings: Eastbound flights are generally routed further south.

As to who decides, a pilot could explain this better than I, but every day oceanic air traffic control centers decide what the most efficient tracks will be for that day based on wind and weather conditions, distances to suitable diversion airports, etc., and those are the routes that are used.

 

[767jetz]

I've never flown the 777, but from what I understand, Polar routes are prefered because they are shorter. However, with a twin engine airplane there are considerations regarding ETOPS (Extended Overwater Ops). ETOPS airplanes need suitable alternate airports within a certain flying time. If an engine fails enroute, the plane must divert to the alternate. Polar routes have limited suitable alternates. So if the weather is bad at one of them, it could preclude the use of that polar route for the 777. This is not a factor for the 747 because if an engine fails they can press on to the destination, hence ETOPS doesn't apply. This is why many pilots prefer the 747 for polar routes.

 

[bcp7]

Oceanic routes use what the call a "track" system. For crossing the North Atlantic Ocean, they are called NAT Tracks, and in the Pacific they are referred to as PACOTS (PACific Organized Track System). They are issued for both eastbound and westbound traffic at different times of the day. Your aircraft must meet certain criteria with respect to maintaining altitude and staying within a certain distance of the track path horizontally. This allows an increase in the number of aircraft which can use these systems. Normally the altitudes used are from FL290 to FL410. You can avoid the track system by flying under it, over it, to the north or south of it, or during times of the day when the track system is not in effect. Eastbound NAT Tracks are used during the morning hours from North America to Europe and westbound tracks in the evening fm Europe to North America.
There are specific entry and exit points for these tracks. The tracks themselves may change on a daily basis, with en route waypoints identified by geographic coordinates.

 

[L1011Ret]

bcp7 has it right. The tracks are not decided by the airline, they are set up by a group sponsored by the airlines. Winds are just about the only factor. The airline can select whatever track it wants but in my experience the computers selected the desired track for any given flight based on cost. Sometimes everybody wants the same track for wind/cost reasons and then the Captain will have to select an alternate track. Very, very occasionally you get on a really undesirable track on the NAT syatem but generally the system worked very well I thought. I did about 600 crossings as I remember.