How do trans-atlantic flights navigate?
PPRuNe Bashaholic
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Deadleg
Fair enough. I suppose we all rose to the various baits being laid.
Sfly
Sorry for misunderstanding the TCAS comments. The position you state later is not how I initially interpreted your original posting. But then that's the benefit of dialogue. Opinions can change.
On the airspace thing, I still think your post is open to question. Do you mean 200 miles after hitting the Oceanic Boundary, or 200 miles after getting your feet metaphorically wet ?? As we're talking aviation, I would take it to mean the Oceanic Boundary. The only way you'd go 200 miles through Oceanic Airspace where ATC is provided by Shannon is if you were exiting the SOTA via 15W. Which of course is entirely feasible via lands End and GAPLI.
In any case, my point was that you believe there is a station called Shannon Oceanic. There isn't. It's ALWAYS Shannon Control, as it's an ATC service provided by a domestic agency. The only area of Oceanic airspace where Shannon provide a service, is the area of the SOTA of which you are obviously well aware. However, the Controlling Authority for that airspace remains SHANWICK Oceanic. The provision of ATS is DELEGATED to Shannon under an international Letter of Agreement. Legal semantics I know but under ICAO we have to do it that way.
F/O Junior
Yeah I get it
Unfortunately much of the correct legal detail and trivia is not in the charts, and quite rightly so. I suppose I should try to remember that this is where the pilot gets the innacurate information from sometimes 
The problem is that in my area I have to work with all the minute levels of detail and international protocol or else the politicians get all upset
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10 West
UK ATC'er
[email protected]
Fair enough. I suppose we all rose to the various baits being laid.
Sfly
Sorry for misunderstanding the TCAS comments. The position you state later is not how I initially interpreted your original posting. But then that's the benefit of dialogue. Opinions can change.
On the airspace thing, I still think your post is open to question. Do you mean 200 miles after hitting the Oceanic Boundary, or 200 miles after getting your feet metaphorically wet ?? As we're talking aviation, I would take it to mean the Oceanic Boundary. The only way you'd go 200 miles through Oceanic Airspace where ATC is provided by Shannon is if you were exiting the SOTA via 15W. Which of course is entirely feasible via lands End and GAPLI.
In any case, my point was that you believe there is a station called Shannon Oceanic. There isn't. It's ALWAYS Shannon Control, as it's an ATC service provided by a domestic agency. The only area of Oceanic airspace where Shannon provide a service, is the area of the SOTA of which you are obviously well aware. However, the Controlling Authority for that airspace remains SHANWICK Oceanic. The provision of ATS is DELEGATED to Shannon under an international Letter of Agreement. Legal semantics I know but under ICAO we have to do it that way.
F/O Junior
Yeah I get it
Unfortunately much of the correct legal detail and trivia is not in the charts, and quite rightly so. I suppose I should try to remember that this is where the pilot gets the innacurate information from sometimes The problem is that in my area I have to work with all the minute levels of detail and international protocol or else the politicians get all upset ------------------
10 West
UK ATC'er
[email protected]
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There is a simple answer to IRS: The aircraft knows where it is at all times.
It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is the greater), it obtains a difference, or deviation.
The Inertial Reference System uses deviations to generate error signal commands which instruct the aircraft to move from a position where it is to a position where it isn't, arriving at a position where it wasn't, or now is. Consequently, the position where it is, is now the position where it wasn't; thus, it follows logically that the position where it was is the position where it isn't.
In the event that the position where the aircraft now is, is not the position where it wasn't, the Inertial Reference System has acquired a variation. Variations are caused by external factors, the discussions of which are beyond the scope of this report.
A variation is the difference between where the aircraft is and where the aircraft wasn't. If the variation is considered to be a factor of significant magnitude, a correction may be applied by the use of the autopilot system. However, use of this correction requires that the aircraft now knows where it was because the variation has modified some of the information which the aircraft has, so it is sure where it isn't.
Nevertheless, the aircraft is sure where it isn't (within reason) and it knows where it was. It now subtracts where it should be from where it isn't, where it ought to be from where it wasn't (or vice versa) and integrates the difference with the product of where it shouldn't be and where it was; thus obtaining the difference between its deviation and its variation, which is a variable constant called "error".
Rod
It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is the greater), it obtains a difference, or deviation.
The Inertial Reference System uses deviations to generate error signal commands which instruct the aircraft to move from a position where it is to a position where it isn't, arriving at a position where it wasn't, or now is. Consequently, the position where it is, is now the position where it wasn't; thus, it follows logically that the position where it was is the position where it isn't.
In the event that the position where the aircraft now is, is not the position where it wasn't, the Inertial Reference System has acquired a variation. Variations are caused by external factors, the discussions of which are beyond the scope of this report.
A variation is the difference between where the aircraft is and where the aircraft wasn't. If the variation is considered to be a factor of significant magnitude, a correction may be applied by the use of the autopilot system. However, use of this correction requires that the aircraft now knows where it was because the variation has modified some of the information which the aircraft has, so it is sure where it isn't.
Nevertheless, the aircraft is sure where it isn't (within reason) and it knows where it was. It now subtracts where it should be from where it isn't, where it ought to be from where it wasn't (or vice versa) and integrates the difference with the product of where it shouldn't be and where it was; thus obtaining the difference between its deviation and its variation, which is a variable constant called "error".
Rod
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Getting across the Atlantic is the easy bit. You only have to report every now and again and you can follow others because there is always loads of people around. If you can't see them, listen to how loud they are on the RT and point to maximize the sound level.
Over land is more difficult because people put hundreds of radio aids or reporting points along your route for absolutely no fathomable reason apart from they're getting a load of back-handers from the suppliers.
Concorde copes with this by two mechanisms. Number one is all these waypoints are on a sort of American Express Card you put in a slot and then go back to calculating the losses on your Tech ISAs
. The American Express card is BLACK of course.
The second mechanism is that the INS cross checks itself with DMEs which progressively remove position error as the plane goes by.
These DMEs are also on the American Express Card so you have time to calculate the losses on our non-Tech ISAs.
Over land is more difficult because people put hundreds of radio aids or reporting points along your route for absolutely no fathomable reason apart from they're getting a load of back-handers from the suppliers.
Concorde copes with this by two mechanisms. Number one is all these waypoints are on a sort of American Express Card you put in a slot and then go back to calculating the losses on your Tech ISAs
. The American Express card is BLACK of course. The second mechanism is that the INS cross checks itself with DMEs which progressively remove position error as the plane goes by.
These DMEs are also on the American Express Card so you have time to calculate the losses on our non-Tech ISAs.
Guest
Posts: n/a
I didn't cover where GPS figures.
GPS is a truly wonderful thing. No doubt about it. It does however have two significant shortcomings.
Firstly it does not have a specific level of accuracy. You have to check before your flight whether a satisfactory constellation of satellites will be available at your intended zone of navigation. Thus there is the risk your 747 has to sit at the gate waiting for the earth to rotate etc. A negligible probability for en-route navigation but your INS is usable in trickier conditions - why lose that?
The second reason, which applies to Concorde, is why buy another area navigation system when you've already got one that works just fine?
It'll be interesting to see whether the Airbus A380 has an INS option.
GPS is a truly wonderful thing. No doubt about it. It does however have two significant shortcomings.
Firstly it does not have a specific level of accuracy. You have to check before your flight whether a satisfactory constellation of satellites will be available at your intended zone of navigation. Thus there is the risk your 747 has to sit at the gate waiting for the earth to rotate etc. A negligible probability for en-route navigation but your INS is usable in trickier conditions - why lose that?
The second reason, which applies to Concorde, is why buy another area navigation system when you've already got one that works just fine?
It'll be interesting to see whether the Airbus A380 has an INS option.
