Credit to the photographs

I would like to thank Brian Losisto (Air Canada's photographer) for always allowing me to post his pictures. (The above thrust lever pic is his). Then there is Kelly Paterson from Calgary and plane spotter "Erik" from Germany. Of course, I have lots myself. On that note, if you feel a photo(s) may be in appropriate or the content I post a bit dubious by all means send me an email. I will ratify it! That's all I ask.

...I hope you enjoy the blog...

Wednesday, November 10, 2010

Great circle stuff

Hi Captain Doug,
I hope you're well! Glad to see you're back to the blog- always enjoy the updates, especially about Air Canada ops and such........

Anyhow, I'm still on tour in Japan and thought I'd send you some photos I took during the flight from YYZ-NRT on .... (around the time you wrote about the low pressure I believe). I was seated in 25K and had an excellent view of the impressive wing flex of the 777-300. I've attached a few photos for you- if you like them, feel free to use them as you wish. I noticed we also took what seemed to me a very northern route (I do this route a couple times each year, and I haven't noticed one this far north yet). Maybe this was due to that massive storm in the midwest? Maybe you could write a bit about the polar routes sometime and what dictates the flightplan and how far north it goes etc...I've always been fascinated by these routes as they overlfly some pretty darn remote areas otherwise never seen! I'll be heading back to YYZ on AC 002 this .... I'll keep my eyes out for anything interesting.

Wishing you safe travels and happy blogging

A small cloud forms at the root of the wing because of the low pressure over the wing and when there is a bit of moisture present.

Even though this picture depicts a northern route it is not a "polar route."
A flat chart like a map depicts a straight line as a curve.

The route you took is not deemed a "polar route" but is a great circle route. Our routing varies daily and is dependent on winds (think prevailing westerlies over Canada), whether we are heading east or west, airspace closure (think military training), airspace cost (some countries charge more than others), space weather (cosmic radiation, etc), availability, enroute weather, etc. The flight plan will figure out the most economical and feasible route.

Great circle routes are difficult to explain. But the shortest distance between two points on a sphere (earth) is curved.

Here's one explanation I found on the internet:

What is "the Great Circle?"

The Great Circle is a concept that takes awhile to understand, but then you'll never forget it. Now, the sliced orange analogy is overused, but it's a good one. Take a pen, mark two dots on an orange (not on the "equator" or straight up and down from each other on a "meridian" - as these are already "great circles"), and then slice the orange between the two dots with the knife angled toward the very center of the orange. If you were then to remove the peel in one piece and flatten it, what appeared to be a straight line on the orange becomes a curved line on the peel. So, the closest distance between two spots on a sphere is actually plotted as a long curve when using a flat representation - like a chart. Put simply: a mercator chart takes the curve out of the world, and you have to put it back in real life.

It is a difficult concept to fathom. There are many sites available to tell you great circle distance. Here's an example...great circle distance between Toronto to Hong Kong is 7810 miles (shortest distance). Many would think a straight line drawn would be shorter by going over California. If I calculated that route Toronto-San Francisco-Hong Kong it would be 9186 miles.

We could use the "polar routes" which fly over the "top." For a Toronto to Hong Kong flight, it shaves off one hour. It might not be the best great circle route but the winds are lighter over the pole. Coming back we tend to fly a more southerly route to capitalize on tailwinds further south.

Lots to think about when flight planning.

NEW*** Here's a link follower YYC Dispatcher sent:


Anonymous said...

Best explanation for 'great circle' I ever heard was at work one day shortly after I was hired. Take a globe, use a piece of string to go from your 'origin' to your 'destination' pulling the string tight over the globe, then look at the 'route' your string takes over the globe.

YYC Dispatcher

Anonymous said...

Just to add another comment, the following website is also a great resource for seeing how it all works:

YYC Dispatcher

Chris Gardner said...

I do see great circle flights overhead in St. John's NL. on a regular basis. They are usually are flights between eastern North America and Europe. I like to call it the 401 Highway 35,000 feet up.

Christer said...

Very interesting Captain Doug! Thanks for the clarification on great circle routes. I also noticed on the return to YYZ that our route was very far south in comparison- right across the Pacific to Seattle, Minneapolis and Kitchener, ON. We were told there were some 130mph tailwinds across the Pacific, and our total flight time was a mere 11h 10mins. for the 6985 miles covered.

By comparison, in the photo you posted of flight 001, travel time was a full 13h 35min. for only 5993 miles across the far north.

Sure seems like a lot of factors determine the flight plan of the day- how much control do pilots have over flight plans? Are they pretty much completely issued by operations when you show up at the airport for your flight?


From the Flight Deck said...

Hi Christer. Welcome back! Sounds like you had quite a "push" going home.

Generally speaking we pilots don't have input into the routing. Having said that, if we see our routing is taking us into known areas of turbulence or other weather we will pick up the phone and query dispatch. There are 700 flight plans generated daily so if every pilot called up contesting things we would never get airborne. lol

Many, including myself the odd time, challenge the fuel requirements and dispatch is very open to suggestions.

Safety is number one!

Captain Doug

From the Flight Deck said...

YYC Dispatcher. I wish I had a globe handy. I tried an orange last night but it wasn't convincing. :)

This will be a possible enRoute question.


From the Flight Deck said...

Thanks YYC Dispatcher. I'll amend my posting to include it. I just tried it. Neat stuff.

P.S I knew you would have lots of comments on this topic!


Anonymous said...

Captain Doug,

My pleasure. This topic can certainly be expanded to include all the other factors that come into play including (but not restricted to) regulatory requirements, political requirements, avoiding war zones, closed airways, and of course, the odd volcano or two as well!

YYC Dispatcher

Lakotahope said...

A couple of times, I've heard discussion coming from a small crowd about this Great Circle Route. This little gimmick you mentioned will be my next endeavor to explain the shortest distance between 2 points is not necessarily a straight line. At least when we are on the earth. Ha.

Glad you still here Captain!

From the Flight Deck said...

Hi Chris the "401" continued along the coast of Nova Scotia where I grew up. Lots of contrails.
In fact, in the southwest part of Nova Scotia one could hear the boom from the Concorde to/from JFK.

From the Flight Deck said...

YYC Dispatcher. Very good points. North Korean airspace is a sensitive one. Plus while flying over eastern Europe there are countries that don't talk to each other and that includes ATC. Speaking of war zones, we flew directly over Kabul, Afghanistan so we didn't want to stray from the "one" air route.
And how can we forget about Volcanoes with the one in Iceland giving us a run for our money? :)


From the Flight Deck said...

Hi Tom. Haven't heard from you in awhile. I hope all is well.

Glad to see you're still here and that I am too!