Polar Flights

[Ethanol]

I know Air Canada is now doing Polar flights and have been for some time now and they use the B777 to do so; Particularly Toronto (YYZ) to Hong Kong (HHH). FYI for those who don't know, they fly north over the north pole and then over Russia and Mongolia into Hong Kong.

I was wondering, They fly North towards the North pole, once they reach Russia and start heading down towards the bottom of the earth which would be South. My main question is once the reach that point does the compass and their heading indicator switch to South heading or the general heading they are flying in? how does that work? they are not really turning to head South they are just flying straight which in their case would be north and at a certain point it just becomes south. I hope I'm making sense describing this and hope everyone understands what I'm trying to say.
This is just one of those curiosity question I have and always wondered how that all worked.
here is the link to a YouTube video of ACA flying the polar flight if your interested. http://www.youtube.com/watch?v=unYKJgUYmi8

Thanks for any replies.

[Masters Off]

I would imagine it would be a mix of GPS work (although the satellite coverage up there must be dismal) and Inertial Navigaion System (INS) in the aircraft on their pre-planned route. Compasses would be useless that close to the magnetic pole and I don't think there'd be any traditional navaid routes, although I'm not sure.

What I do know, is that they'd have to be precise, and wouldn't leave it to VFR naviation (i.e. compass) instead it'd be some form of IFR routing.

So, now you've got my curiosity. Any Big Iron drivers want to comment on how it's done?

[2550]

Im sure they get out those finding suns true bearing charts and scratch their heads like i did on the exam until the compass starts working again...

[ogopogo]

I would imagine it would be a mix of GPS work (although the satellite coverage up there must be dismal)


GPS satellites are in Medium Earth Orbit MEO (<-clickie)and there is nowhere on earth that isn't covered. I think you're thinking of the communications and broadcast sats which are in GEO (<-another clickie) and have limited view at +/- 70deg lat.

[Rockie]

There are four established polar routes going from North America straight over the top to Russia/Asia. The route taken is dependant on minimum time track to destination of course, but also considers solar radiation levels and temperature limits for the aircraft as well. Flights have been rerouted because either the level of solar radiation on the least time track was too high, or the temperature was below -65C for too long which would risk fuel freezing.

In the north the heading reference is switched to true which is maintained until well south into Russia again. Navigation is via INS/GPS, and contrary to a previous comment GPS satellite coverage is excellent over the north because in actual fact more satellites could be in view at any one time than down near the equator, although they may be very low on the horizon. The GPS satellites are on an inclined orbit that crosses the equator at a 55 degree angle meaning in half an orbit they go from 55 degrees north to 55 degrees south, so even standing on the ground at the north pole you should have at least 6 satellites in view at any given time.

Only one of the routes actually comes relatively near the North Pole but I can't remember the distance offhand. The displayed heading on the Navigation Display always shows true heading while up there and does indeed shift around to southerly. The closer you are to the pole the faster that occurs because of the diverging lines of longitude and you can actually watch the compass moving even though you are wings level.

Magnetic compass is of course absolutely useless up there, but transport aircraft don't measure magnetic heading anyway. The navigation system always knows where true north is through the inertial system and then applies a variation derived from the database and its known position to display a calculated magnetic heading. The displayed heading can be manually switched to true, but if you forget to do that it switches above a certain latitude automatically anyway. Some aircraft can also display grid headings that effectively does away with the problems of northern flying in true or magnetic heading. It's basically a special map projection that allows someone to fly from point A to point B in a straight line and the displayed track will never change even though it may not be anywhere near the true track. The military used to use it and may still and so might some airlines, but Air Canada doesn't because it isn't necessary.

[habs.fan]

Flights have been rerouted because either the level of solar radiation on the least time track was too high, or the temperature was below -65C for too long which would risk fuel freezing.

What's the deal with this? With turbine engines can't we find something, anything that burns and stops fuel from freezing? Or is the chemistry more complex than I'm assuming it to be?

edit: I know about Prist and such, but I mean something a little bit more intense that goes to, say, -273C or something.

[loopy]

Canadian North still uses grid navigation. I don't know about anyone else.

[Ethanol]

Thanks all!
My question was pretty much answer for the most part.

[Meatservo]

Sometime or other when I was studying navigation myself, I came across something written by an Airbus pilot who described switching to grid navigation for polar routes. I can't recall where I might have read that. But it seems that some companies do that.

[Kestral]

Grid Navigation is used in Antarctica by the U.S. Air Force, Air Guard and KBA aircraft on U.S.A.P contracts operating in to U.S. bases. South Pole Station ski-way for example is on a Grid heading of 020 degrees. On approach an aircraft would be crossing several lines of Longitude in a matter of seconds. I also believe that the Runway at Thule Air Base in Greenland is in Grid.

Grid is basically based and the concept of a flat earth with 0 degrees or the Prime Meridian separating West & East. This provides a so called constant reference direction with no convergence of lines on Longitude as would be the case with True headings. Grid North would therefor be 360 degrees north along the Prime Meridian with Grid South running along the 180 degree line of Longitude through the Pacific Ocean. Wind direction at South Pole Station is given in Grid otherwise the wind be always be from the north.

Once you are able to grasp the concept it is actually quite practical when operating in either Polar Region. In simple terms it's just like slicing the earth in half and laying it out flat like on a wall map that you used to study countries on when you were in Grade 4.

[Masters Off]

I do remember now the difference on those satellites, thanks.

Now, someone made the comment on it being too cold for too long, is this not what brought down the BA 777 into heathrow? Something with cold fuel being frozen in a filter or something to that effect (and when more power was added, it was blocked by a cold ice/slush mix, not allowing the increase of power?

Sounds like they could find a way to heat the fuel, might solve some problems...not that this is something I know at all, just what I've gathered.

[Rockie]

There are fuel/oil heat exchangers of course, but a special system to heat the fuel beyond that is simply not necessary. It takes prolonged exposure to extreme low temperature (-65) to lower the temperature of the fuel to the point where freezing is a threat. It is easier and likely much cheaper to flight plan around it the odd time it extensively exists on the most desirable route, and if it's encountered unexpectedly a descent should solve the problem.

[just curious]

[longjon]

I believe the Bombardier Global has fuel heaters for this.

[Krashman]

the 777 300ER switches from magnetic to true to grid close to the pole on the primary nav display but when we fly over the pole all the way points are in the FMS.

There are routes that we follow depending on the day and the winds. A few months ago going JKF to HKG we went straight north then more north east once we hit greenland. the closest suitable airport for us was somewhere in finland.

[hst]

Navigation in the polar regions for modern wide body aircraft isn't complicated unless Lateral Navigation capability is lost. Our procedure is to plot grid heading (in the Northern Control Area) on a polar chart as back up. Navigation is waypoint to waypoint on one of 4 permanent routes. If fuel temperature is an issue one of 3 options exist. Change altitude, change track or speed up. The B777 automatically depicts 'Grid" at 70N and our procedures are to change the heading reference selector to True while in the polar region.

Btw there is very little wind in the polar region so the rides are almost always smooth.

[ettw]

That of course is on the dash of ACs 777.

ETTW