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Dougal

What exactly is this website for?

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Any direct path between two points on a sphere (globe) will be shown differently depending on the type of map you look at, and the orientation of the map. A Great Circle is the shortest distance between two points on a sphere (globe). So a Great Circle Route between two cities, say New York and London, would actually be flown in a straight line, but when shown on a flat map MIGHT appear to be a curved route instead (depending on the orientation of the flat map).The link below explains the concept in more detail.http://en.wikipedia.org/wiki/Great_circleThe website you listed just allows you to determine a Great Circle Route between any two places on the Earth.FalconAF

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When calculating a flight path between two points on the Earth, the Earth's radius must be taken into consideration.Hence, we really don't fly in a straight line within a three dimensional space.

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As FalconAF explained, it's a tool for route calculation, one of many you can find online. The only other thing on that site you might not be familiar with is the ETOPS acronym, which has a bearing on long-range flying:ETOPS stands for Extended Twin-engined Operational Performance Standards. It is a ruling which was first approved by the US Federal Aviation Administration in 1985, and subsequently adopted by most other aviation governing bodies. Prior to that date, twin-engined civilian aircraft were not allowed to operate flights that involved sections where they would be more than 60 minutes' flying time from a suitable diversion airfield. That rule was introduced in the early 1950s, and was based on the lower reliability of aero engines around that time. This is one of the reasons why triple-engined aircraft such as the L1011 Tristar, DC-10, B727 and Trident were created, because they were able to fly across the Atlantic and Pacific in the days of turbojets when reliability in jet engines was not as good as what we see these days; the 60 minute ruling was waived in the mid 1960s for aircraft with three engines.The early successes of Airbus Industries breaking into the market for aircraft sales in the 1970s was in some ways by virtue of the company exploiting exceptions to the 60 minute rulings. Outside the continental US, before ETOPS was introduced, aircraft could follow International Civil Aviation Organisation (ICAO) rules, which allowed for 90 minutes of flight without a suitable diversion for twin engined aircraft. This led to huge popularity and sales of larger wide-bodied twin-engined aircraft such as the A300, which with two rather than three engines, were cheaper to operate. It's also why we saw some US airlines getting into buying European-manufactured types when they traditionally would have only ever considered acquiring home-grown aircraft, as a consequence, it was a spur for Boeing to develop their own larger twin-engined airliners. The latest two types to join battle for sales around these rulings being the Airbus A350 and Boeing 787 Dreamliner.With the increased reliability of engines such as the Rolls Royce 877, Pratt and Whitney 4077 and the General Electric 90, safe, extremely long range twin-engined operations became much more feasible, and so we began to see aircraft such as the Boeing 777 and 767 being made, and it was the ETOPS rulings which covered the operation of these aircraft. Much of the ETOPS discussion centered on the fact that these aircraft usually only had two crew members as well as only two engines, following the demise of the flight engineer position on board such aircraft, owing to reliance on more computer systems. This is why you often see ETOPS aircraft with crew rest facilities built into them, so that more than one crew can be carried.But even today, with ETOPS rulings in place, there are still parts of the world where three-engined aircraft offer more flexibility in terms of where they can legally fly, chiefly because the two main governing bodies which grant an aircraft ETOPS status sometimes disagree. The FAA has often granted 180-minute ETOPS ratings to aircraft upon introduction into service (the Boeing 777 was one such aircraft to get that rating and was in fact the first one to have it). The more conservative Joint Aviation Authorities (which includes the ICAO and usually governs European operations) disagreed with the FAA on this matter and only granted the 777 a 120-minute rating initially (later extending it), but the JAA will usually only extend such a rating after a type has demonstrated a full year of trouble-free flying, although in the case of the 777, they actually wavered a bit on their decision and eventually gave it a 138 minute ETOPS rating (the addition of 15 percent to its original 120 minute ETOPS rating), to allow the 777 to cross the Atlantic even if the traditional mid Atlantic diversion airfield in Greenland was closed for operations. But it now has a JAA-approved 180-minute rating. The definition for a year of trouble-free operation for ETOPS is typically classed as 'no more than two engine shutdowns in every 100,000 hours of operation', which gives you some idea of how reliable modern high-bypass turbofans are these days!Needless to say, there have been frequent accusations bandied about that the JAA favours the Airbus business model and the FAA favours the Boeing strategy, and it's probably true in both cases, to at least some extent.ETOPS 180 minute ratings make almost all the earth's surface reachable by aircraft flying under those rules - but not all of it, there is still about 4 percent of the destinations in the world outside it - which is why you see triple-jets like the DC-10, 727 and MD-11 still in service, especially with freight companies, where they often have to go to extremely remote destinations.There are some interesting exceptions to ETOPS and some surprising things too, and the ability for an aircraft to meet those requirements often affects aircraft sales - in the US for example, private jets do not have to follow ETOPS rules, in Europe (under the JAA) they do, which is why the shorter-ranged Cessna Citation Mustang has sold well in Europe. Some flights across the Southern Pacific and down to Antarctica are not permitted with twin-engined civilian aircraft, and is one of the reasons why Quantas has shown an interest in the A380, also one of the reasons why Boeing is developing its larger 747. Most military aircraft are exempt from the ETOPS rules, which is why the US Navy can get away with using the Boeing 737 as the basis for its new Poseidon anti-submarine patrol aircraft which comes into service this year. ETOPS aircraft have to carry some things which often surprises people; for example, they have to have equipment on board to ensure the survival of passengers if the aircraft diverts to a remote location and has to be there a while. So they obviously need more food on board and items of that nature, but they also need more sophisticated medical equipment, such as defibrilators, and of course the crews have to be suitably qualified to use all that stuff too.Al

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When calculating a flight path between two points on the Earth, the Earth's radius must be taken into consideration.Hence, we really don't fly in a straight line within a three dimensional space.
OMG. Well...in that case, I guess we should also include calculations that take into consideration the relative orbits of the Earth around the Sun, the Sun around the center of the Galaxy, the Galaxy's relative motion in relation to the rest of the Galaxies in our immediate Galaxy Cluster, etc, etc.I meant a straight line depicted on a two-dimensional MAP, for crying out loud.PS - Chock...nice in-depth reply. Well done.FalconAF

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OMG. Well...in that case, I guess we should also include calculations that take into consideration the relative orbits of the Earth around the Sun, the Sun around the center of the Galaxy, the Galaxy's relative motion in relation to the rest of the Galaxies in our immediate Galaxy Cluster, etc, etc.I meant a straight line depicted on a two-dimensional MAP, for crying out loud.PS - Chock...nice in-depth reply. Well done.FalconAF
Now that this comes up, many people are aware that FSX gets... creative when generating some GC flightpaths on its own. Certainly older MSFS iterations have had problems with GC navigation. By plotting alongside a known GC route, you can fudge the numbers for your own flightplan and make a decent enough approximation for most flight sim purposes. Jeff Shyluk Senior Staff ReviewerAVSIM

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In maritime navigation, in the days before computers and widespread electronic navigation, it was necessary to develop standard methods of computing courses and distances so they could be incorporated in the form of tables or specialized slide-rules. These were referred to as "the sailings". Commonly used sailings were developed based on the mid-latitude method, the Mercator method, and the great circle method. Great circle sailings generally involve equations using secants and cosecants, and tables for these have been available in the past, such as H.O. 211.Aeronautical charts typically use the Lambert conformal projection, so that straight lines approximate great circles.scott s..

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I guess I'll add this to my list of reasons why I don't want to move from Florida to Canada.

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I guess I'll add this to my list of reasons why I don't want to move from Florida to Canada.
:( Uhhh, sorry, but a curious Canadian wants to know ... what's the relationship between Great Circle routes and not wanting to live in Canada?

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Thanks for such great feedback and information guys - much appreciated.

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:( Uhhh, sorry, but a curious Canadian wants to know ... what's the relationship between Great Circle routes and not wanting to live in Canada?
The farther north you go the more of a factor the great circle route becomes as the shortest distance between two points. At the equator it's not a factor.Thanks for asking.

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The farther north you go the more of a factor the great circle route becomes as the shortest distance between two points. At the equator it's not a factor.Thanks for asking.
Huh???? You wanna run that one by me again??? It makes no difference whatsoever "how far north you go" in determining the shortest distance between two points on the Earth's surface. The shortest distance on a sphere (globe) is a straight line drawn on the circumference of the sphere (globe) between the two points, regardless of where the starting and ending points are located. The distance (length) of the LINE SHOWN on a graphical image, like a map, will vary greatly depending on the frame of reference of the two-dimentional map. A Great Circle Route that exists totally either North or South of the equator, when shown on a Polar Projection map, will be shorter than one shown on a map using the equator as the reference line, but the actual distances of the ROUTE, when flown, will be exactly the same.If you use a flight planning program like FS Commander, display a GPS Direct flight plan in both the "regular" map mode and then the "Round World" map mode to understand the difference. In "Round World" mode, FS Commander will show the "frame of reference" for the flight plan centered ON the flight plan itself (the Great Circle Route), and the flight plan's "line" will always show as a straight line, not curved at all.FalconAF

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Huh???? You wanna run that one by me again??? It makes no difference whatsoever "how far north you go" in determining the shortest distance between two points on the Earth's surface. The shortest distance on a sphere (globe) is a straight line drawn on the circumference of the sphere (globe) between the two points, regardless of where the starting and ending points are located. The distance (length) of the LINE SHOWN on a graphical image, like a map, will vary greatly depending on the frame of reference of the two-dimentional map. A Great Circle Route that exists totally either North or South of the equator, when shown on a Polar Projection map, will be shorter than one shown on a map using the equator as the reference line, but the actual distances of the ROUTE, when flown, will be exactly the same.If you use a flight planning program like FS Commander, display a GPS Direct flight plan in both the "regular" map mode and then the "Round World" map mode to understand the difference. In "Round World" mode, FS Commander will show the "frame of reference" for the flight plan centered ON the flight plan itself (the Great Circle Route), and the flight plan's "line" will always show as a straight line, not curved at all.FalconAF
If I'm in Newfoundland and fly to a point directly west of me by flying directly west by compass, I am not flying the shortest distance between two points. If I'm in Ecuador and fly to a point directly east of me by flying directly east by compass, I am flying the shortest distance between two points. No?

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If I'm in Newfoundland and fly to a point directly west of me by flying directly west by compass, I am not flying the shortest distance between two points. If I'm in Ecuador and fly to a point directly east of me by flying directly east by compass, I am flying the shortest distance between two points. No?
Yes and No.You are confusing Magnetic Headings with the Great Circle Route concept. You cannot fly a Great Circle Route without heading changes occuring (in almost all cases), but this does NOT mean that you actually TURN the aircraft during the flight. The relationship between TRUE North and MAGNETIC North will constantly change due to the Earth's magnetic field NOT being aligned with the "true" geographical North Pole.Load a GPS Direct flightplan, say from New York to London. The TRACK of the flight will not change...you will never have to manually make a left or right turn during the flight...you will fly a "straight line" all the way there. But your MAGNETIC HEADING will change over time as the aircraft's relationship to Magnetic North changes. On takeoff from New York, your initial heading will be northeast. Approaching London, it will be southeast. But you never "turned" the aircraft right at any time during the flight. You flew a constant "straight line" all the way between New York and London. The heading changes happen because of the nature of Great Circle Routes (and Magnetic Variation).Another way to look at it is start a flight at the equator, and take off due north at 360-degrees magnetic. As soon as you cross the Magnetic North Pole, your heading will change to 180-degrees...SOUTH...but you will still be flying in a straight line and never have turned the aircraft at all.This is why when you look at a map projection of a spacecraft's track orbiting the Earth, the "line" curves up and down on the map. The curved line is actually a complete Great Circle Route around the entire globe. Even though the spacecraft was launched using an INITIAL heading at the moment of launch, the ACTUAL heading of the spacecraft changes relatative to the Earth's Magnetic North as it circles the globe. But the TRACK never changes...the spacecraft is always still tavelling in a "straight line" around the Earth. In orbital mechanics terms, this is referred to as the "inclination" of the spacecraft relative to the Earth's equator. The same concept applies to aircraft flying Great Circle Routes, even though the route doesn't circle the entire globe. If the route was extended around the entire globe, then the same track would show for the aircraft as it would for the spacecraft, if they both were "launched" from the same starting point with the same initial heading. FalconAF

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Yes and No.You are confusing Magnetic Headings with the Great Circle Route concept. You cannot fly a Great Circle Route without heading changes occuring (in almost all cases), but this does NOT mean that you actually TURN the aircraft during the flight. The relationship between TRUE North and MAGNETIC North will constantly change due to the Earth's magnetic field NOT being aligned with the "true" geographical North Pole.Load a GPS Direct flightplan, say from New York to London. The TRACK of the flight will not change...you will never have to manually make a left or right turn during the flight...you will fly a "straight line" all the way there. But your MAGNETIC HEADING will change over time as the aircraft's relationship to Magnetic North changes. On takeoff from New York, your initial heading will be northeast. Approaching London, it will be southeast. But you never "turned" the aircraft right at any time during the flight. You flew a constant "straight line" all the way between New York and London. The heading changes happen because of the nature of Great Circle Routes (and Magnetic Variation).Another way to look at it is start a flight at the equator, and take off due north at 360-degrees magnetic. As soon as you cross the Magnetic North Pole, your heading will change to 180-degrees...SOUTH...but you will still be flying in a straight line and never have turned the aircraft at all.This is why when you look at a map projection of a spacecraft's track orbiting the Earth, the "line" curves up and down on the map. The curved line is actually a complete Great Circle Route around the entire globe. Even though the spacecraft was launched using an INITIAL heading at the moment of launch, the ACTUAL heading of the spacecraft changes relatative to the Earth's Magnetic North as it circles the globe. But the TRACK never changes...the spacecraft is always still tavelling in a "straight line" around the Earth. In orbital mechanics terms, this is referred to as the "inclination" of the spacecraft relative to the Earth's equator. The same concept applies to aircraft flying Great Circle Routes, even though the route doesn't circle the entire globe. If the route was extended around the entire globe, then the same track would show for the aircraft as it would for the spacecraft, if they both were "launched" from the same starting point with the same initial heading. FalconAF
Anyway, it gets too cold in Canada. :(

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