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Old 19th August 2019, 13:46   #16
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by suresh_gs View Post
Can you explain how aircraft cross the oceans without any radar coverage. Then how will the ATC track these planes.
Did you watch the video? ATC does not track the planes as such.

It staggers them onto the route, ensuring sufficient horizontal and vertical separation along the route. Planes will give position reports every ten minutes.

So ATC knows where the planes will be, based on simple dead reckoning and intermediate position updates.

Think of these tracks/airway as simple highways. ATC tells you when to enter it and at what speed you must travel. They know the entry point and your speed, so they can calculate where you will be. There will be position reports, so that makes it even more precise.

The video shows that they have separate tracks for East-West and West-East traffic. So no danger of head on collisions. They will also stagger the planes vertically. E.g. the first plane to get onto the track will get FL300, the next one FL330 etc. Horizontal and vertical separation in these non radar coverage areas are a lot more then under radar coverage.

It works very well, very safe and these days entering the NAT is all automated. In the old days, pilots had to talk to ATC to get their NAT slot. all done by computers these days. I don’t think we have ever seen any major incident on the NATs. Across other areas in the wold that do not have radar coverage, similar systems and procedures are in place.

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Old 19th August 2019, 13:59   #17
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by V.Narayan View Post
....
With regard to fuel freezing points @vigsom is right that the typical jet fuel freezes at -47 deg C*. If the stratosphere is at -55 deg C then why does the fuel not freeze. The risk of fuel freezing is there but limited in today's jet airliners. ...
The fuel may not freeze, but water particles in the fuel may freeze. Of course, it has happened.

https://en.wikipedia.org/wiki/British_Airways_Flight_38 - The first 777 hull loss.

As rightly pointed out, the risk is limited though.

Last edited by bsdbsd : 19th August 2019 at 13:59. Reason: added a line.
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Old 19th August 2019, 14:01   #18
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by Jeroen View Post
Did you watch the video? ATC does not track the planes as such.

It staggers them onto the route, ensuring sufficient horizontal and vertical separation along the route. Planes will give position reports every ten minutes.

So ATC knows where the planes will be, based on simple dead reckoning and intermediate position updates.

Think of these tracks/airway as simple highways. ATC tells you when to enter it and at what speed you must travel. They know the entry point and your speed, so they can calculate where you will be. There will be position reports, so that makes it even more precise.

The video shows that they have separate tracks for East-West and West-East traffic. So no danger of head on collisions. They will also stagger the planes vertically. E.g. the first plane to get onto the track will get FL300, the next one FL330 etc. Horizontal and vertical separation in these non radar coverage areas are a lot more then under radar coverage.

It works very well, very safe and these days entering the NAT is all automated. In the old days, pilots had to talk to ATC to get their NAT slot. all done by computers these days. I don’t think we have ever seen any major incident on the NATs. Across other areas in the wold that do not have radar coverage, similar systems and procedures are in place.

Jeroen
Does that imply that radars are only used to detect when the plane is about to enter a country's air space and that the ATC follows a prescribed route for all planes entering or leaving the airport ?
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Old 19th August 2019, 14:48   #19
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by suresh_gs View Post
Does that imply that radars are only used to detect when the plane is about to enter a country's air space and that the ATC follows a prescribed route for all planes entering or leaving the airport ?

Not quite sure I understand your question; What I explained is only applicable for areas where there is no radar coverage.

All aircraft, above certain altitudes, follow prescribed routes, irrespective of radar coverage or not.

For entering and leaving airport there are also designated routes specific for an airport and specific runway

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Old 20th August 2019, 00:11   #20
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by suresh_gs View Post
Does that imply that radars are only used to detect when the plane is about to enter a country's air space and that the ATC follows a prescribed route for all planes entering or leaving the airport ?
Looking at your interest, I would recommend you to follow CaptainJoe on youtube and watch all series of Air Crash Investigation (great source of knowledge). My personal favourite is Gimli Glider(Air Canada Flight 143 which ran out of fuel due to inadequate training on metric units)

Last edited by purohitanuj : 20th August 2019 at 00:14.
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Old 21st August 2019, 18:00   #21
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by Rahul Bhalgat View Post
M
2. Directional indication will be more and more weak (and hence less and less accurate) as you approach the north pole. When you are directly above the north pole, north is beneath you! Only after you travel a certain distance after crossing the north pole, you will start getting proper direction signals. By this time, you may have drifted from your path; you need to correct it.
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Originally Posted by SCORPION View Post
In addition to the above,
The only reliable equipment to tell you what direction you are moving in, is the magnetic compass. Gyros and satnav systems can fail because they rely on technology and need external power. The Magnetic Compass becomes unreliable as we approach the magnetic poles.
.
Sorry, I had not noticed these comments before. Let me try and simplify how modern commercial jets navigate. Magnetic compasses simply do not come into the equation! Although most aircraft might still have a magnetic compass as a (legally required) back up.

Modern planes have (for decades already) a Flight Management System or FMS.
The FMS takes inputs from multiple sensors to determine a position. It also assesses the accuracy of each position for each sensor and determines how it mixes and present the so called FMS position to the pilots.

Sensor on most wide bodies are at least:
- Three independent GPS sensor
- Three independent IRU ((Inertial Reference Units)
- Multiple Radio receivers. (e.g. VOR, NDB, DME etc)

So the position of an aircraft is determined using multiple inputs, from multiple different type and kind of sensors. It takes into account accuracies, known drift and such factors. There are different kinds of approaches on how these different inputs (positions actually) are mixed into a single position and a so called ANP. ANP stands for actual navigation performance. Each airspace has a a so called RNP (Required Navigational performance. The ANP must be less than the RNP for a jet to pass through that airspace. It is the basis on how separation between aircraft is achieved/maintained.

Going across the polar region requires a somewhat different approach. Most FMS have a so called polar ops included these days. Roughly above latitude 84 degrees the FMS will switch to Polar Mode. In polar mode, the FMS will calculate the position differently.

Roughly (oversimplifying here) below 84o all references to heading will be magnetic north. Above 84o all references to heading will be to True North.

So whereas a magnetic compass becomes useless in Polar regions, it is not a problem for aircraft. Reliability of GPS, IRU, Radio Receivers etc. is very, very high to start with and all systems have at least 2/3 independent sensors to start with.

I oversimplified the FMS and Polar Operation a bit. If you want to understand a bit more detail, here is an interesting Boeing Bulletin.

http://www.boeing.com/commercial/aer..._by_model.html

It is a bit dated, not so much in explaining the principles but the list of capabilities per aircraft type. These have increased/expanded over time

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Old 11th September 2019, 13:38   #22
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by Jeroen View Post
There are different kinds of approaches on how these different inputs (positions actually) are mixed into a single position and a so called ANP. ANP stands for actual navigation performance. Each airspace has a so called RNP (Required Navigational performance. The ANP must be less than the RNP for a jet to pass through that airspace.
ANP must be less or more than RNP sir?
I don't have much knowledge in this area so kindly excuse if question looks dumb.
Logically, if ANP is more than RNP, it means that the location of the flight is more accurate. Please correct me where am I going wrong.
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Old 11th September 2019, 19:13   #23
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by coolmind View Post
ANP must be less or more than RNP sir?
I don't have much knowledge in this area so kindly excuse if question looks dumb.
Logically, if ANP is more than RNP, it means that the location of the flight is more accurate. Please correct me where am I going wrong.
It’s the exact opposite to your thinking.

RNP is what is required for an aircraft to enter that particular airspace. So the aircraft positioning system must do better (more accurate) than what is required.

If for instance the RNP is given as 5, it means that the aircraft navigation system must be able to calculate its position accuracy within a 5 mile radius.

In order to comply, the ANP needs to be smaller. The smaller the number the better the actual and or required accuracy. So in this example of a RNP of 5, the ANP needs to be less than 5.

Hope this helps

Jeroen
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Old 11th September 2019, 22:17   #24
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Default Re: Air India becomes 1st Indian airline to fly over the North Pole

Quote:
Originally Posted by coolmind View Post
ANP must be less or more than RNP sir?
I don't have much knowledge in this area so kindly excuse if question looks dumb.
Logically, if ANP is more than RNP, it means that the location of the flight is more accurate. Please correct me where am I going wrong.
Quote:
Originally Posted by Jeroen View Post
It’s the exact opposite to your thinking.

RNP is what is required for an aircraft to enter that particular airspace. So the aircraft positioning system must do better (more accurate) than what is required.

If for instance the RNP is given as 5, it means that the aircraft navigation system must be able to calculate its position accuracy within a 5 mile radius.

In order to comply, the ANP needs to be smaller. The smaller the number the better the actual and or required accuracy. So in this example of a RNP of 5, the ANP needs to be less than 5.

Hope this helps

Jeroen

Confusion of coolmind appears to be because of the word P (Performance) in RNP / ANP.

Coolmind, here the Performance actually means the amount of imperformance! It is the amount of inaccuracy. And hence as the Jeroen says, ANP figure must be smaller then the RNP figure.
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Old 11th September 2019, 23:59   #25
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Default Air India becomes 1st Indian airline to fly over the North Pole

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Originally Posted by Rahul Bhalgat View Post
.



Coolmind, here the Performance actually means the amount of imperformance! It is the amount of inaccuracy..

????????

If the accuracy of a navigation system is 5, what would its inaccuracy or imperformance be?

https://www.google.nl/amp/s/www.collinsdictionary.com/amp/english/inaccuracy

Jeroen

Last edited by Jeroen : 12th September 2019 at 00:01.
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