[vigsom]

After creating a record of sorts by flying out over the Pacific and flying in via the Atlantic, Air India's DEL-SFO flight, cut across latitudes instead on Thursday to fly over zero degree north.

Source :

https://m.economictimes.com/industry...w/70701750.cms

I couldn't find a thread on transatlantic non stop flights hence created this thread.

[V.Narayan]

A good step forward for Indian aviation. Without taking away anything from the pilots and flight planning team it is a sign of how weak Indian carriers are with regard to Indian international traffic that it took so long for this landmark to be crossed. The North Pole route was first flown successfully by a passenger carrying airliner in 1954 by SAS flying Douglas DC-6B's. And by 1956 it was a regular affair. The navigation work load was heavy enough to need two navigators at a time working together. Incidentally there are flights over the Antarctic too - longer, more lonely, less known - between Australia and South America.

[Shreyans_Jain]

What’s the big deal here? To the best of my knowledge, flights take the geodesic path to their destination with alternations subject to airspace restrictions and endurance limitations. Is the North Pole route actually shorter? If so, why did we never do it before? Are there any special challenges for a commercial airliner to do this? Or is this just about bragging rights?

[SmartCat]

Normal route and polar route between major cities of the world:



It is a bit baffling to look at all the countries on our beloved earth from "the top"

[Rahul Bhalgat]

Originally Posted by Shreyans_Jain

Are there any special challenges for a commercial airliner to do this? Or is this just about bragging rights?

My guess about the possible challenges:

1. Lack of nearby strips for emergency landing.

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.

[SCORPION]

Originally Posted by Rahul Bhalgat

My guess about the possible challenges:

1. Lack of nearby strips for emergency landing.

2. Directional indication will be more and more weak (and hence less and less accurate) as you approach the north pole.

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.

3. Weather conditions are extreme in the polar regions most of the year. Weather is very unpredictable.

4. Fuel management is more difficult because of very low temperatures which may cause the fuel to freeze. Additional measures are required for fuel management.

5. Satnav systems like the GPS do not work well in higher latitudes above the Arctic circle because they are not polar orbiting satellites. Other systems like GLONASS may need to be used.

6. Communication also becomes difficult because, like the GPS satellites, many of the communication satellites do not have a foot print in the polar regions. VHF and HF communication may need to be resorted to with no proper ground stations available for reliable communication.

7. Additional training for the flight crew is required for polar transit.

8. The aircrafts need to be equipped with additional equipment.

Trivia: With the ice melting in the Arctic area, ships have started polar navigation and LNG vessels regularly take the polar route from North Russia to Europe and US.
Most of the challenges faced by the airline industry applies to ships as well and most of the points mentioned above hold good for ships on polar transit routes, except may be the requirement for a safe landing place and fuel management is easier.

[Motard_Blr]

Originally Posted by SCORPION

...

4. Fuel management is more difficult because of very low temperatures which may cause the fuel to freeze. Additional measures are required for fuel management.

....

Would the air temperature at stratospheric cruising altitude around the poles be any different from that at lower latitudes?

[vigsom]

Originally Posted by SCORPION

4. Fuel management is more difficult because of very low temperatures which may cause the fuel to freeze. Additional measures are required for fuel management.

True; but the freezing point of Jet fuel is -47 deg.C max. So fuel management wouldn't be an issue.

There is another grade of Jet Fuel called B which has a freezing point of -60deg.C; but this grade is rarely used.

[V.Narayan]

Originally Posted by Motard_Blr

Would the air temperature at stratospheric cruising altitude around the poles be any different from that at lower latitudes?

Originally Posted by vigsom

True; but the freezing point of Jet fuel is -47 deg.C max. So fuel management wouldn't be an issue.

The air temperature in a theoretically static atmosphere will be similar over the poles as over the equator at say 35,000 to 40,000 feet which is typical airliner cruise altitude and which is well into the stratosphere. The stratosphere starts roughly at 30,000 feet onwards up to roughly 170,000 feet. Temperatures in the lower part of the stratosphere is interestingly constant at about -55 deg C. This is largely the same all over the globe. In the middle and upper reaches of the stratosphere the temperature inverts and warms up to around -5 deg C. to -3 deg C. at ~170,000 feet.

The layer below the stratosphere, the troposphere i.e. the bottom of the ocean of air has high speed vertical currents up to several metres per second, say 2000 feet per minute - which is the rate at which you see airliners climb as they take-off. This rapid vertical movement pushes the air (and its corresponding coldness or warmth) from the earth's surface up into the lower reaches of the stratosphere and that can temporarily cause a difference between the air over the poles being colder than the air at the equator at say 35,000 feet. But weather phenomena is usually more complex than this simple explanation. So you could easily encounter a -60 deg C. over the equator at airliner cruising altitude as you could experience a warmer -50 deg C at the poles. And wait we haven't discussed the effects of humidity...... and diurnal effects yet:-)

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 being a huge body of fluid is at ground temperature when it takes off and retains its organic warmth for several hours as the aircraft flies! Nevertheless the pilot is sent a warning when the fuel tank temperature gets to around -44 deg C. This applies to all flights not just the ones over the pole. The risk of fuel freezing was real when propeller airliners like the DC-6B, DC-7C and Super Connies flew in the 1950s because their altitudes were in the 20,000 to 24,000 feet spectrum, well inside the troposphere and the temperature on the ground had a very real effect there. Fuel freezing is not alone a function of the ambient temperature outside but the real temperature being experienced by the skin of the aircraft which is affected by friction at 850 to 900 kmph. So while the air outside may be at say -55 deg C the temperature of the skin would be much warmer at roughly -25 deg C. The skin of the aircraft being 27 to 37 deg C warmer than the ambient air is typical at airliner speeds & cruising altitudes.

Sorry guys you got me going ... Saturday morning, family has gone galavanting, peace in the house, mug of coffee next to me.....

NB: all figures are indicative and vary in reality based on actual conditions. But directionally these figures are correct for purposes of explanation.
*-47 deg C is the standard set. In practise most refineries today produce jet fuel that actually freezes at a few degrees colder

[Jeroen]

Originally Posted by Motard_Blr

Would the air temperature at stratospheric cruising altitude around the poles be any different from that at lower latitudes?

In addition to the clarification provided by Vigsom and V.Narayan, I have dug up the respective Non Normal Checklist for a low Fuel Temperature alarm. (Cargolux, 747-400)

On modern jets it is rare to happen these days. Three options, increase speed which will increase friction and thus temperature. Change altitude and find a warmer air mass.



As V.Narayan explained at higher altitudes the temperatures are low, but very consistent. And it takes a long time for the cold to soak into the fuel.

The B fuel as mentioned by Vigsom is primarily used in areas where you have very low temperatures on the ground! Because then the fuel is/can be exposed for a very long time. For instance in parts of Russia. I worked in Yakutz, Siberia for some months, a long time ago. -50oC was the norm!

It is very rare these days to encounter actual problems with low temperature fuel these days. But it does happen now and then.

Have a look:

http://www.avherald.com/h?article=4009e4c6/023&opt=0

Jeroen

[Shreyans_Jain]

From what V Narayan, Jeoren and Vigsom have written, my understanding is that freezing of fuel and low ambient temperatures are not really a challenge for commercial aircrafts to fly over the poles, especially when taking off from a tropical country like ours. The issue seems to be navigation and satellite support, or the lack of it.

Civil aviation is a highly automated process with pre decided flight plans and the plane pretty much stays in autopilot while cruising. So, how safe is it for them to fly 300-400 passengers over the North Pole when satellite or GPS coverage is patchy if not entirely inexistent? Do DGCA norms even allow this? What is the global SOP here? If civil airliners from US or Europe regularly fly over the North Pole, surely, navigation must also not be that much of a problem.

[Jeroen]

Originally Posted by Shreyans_Jain

Civil aviation is a highly automated process with pre decided flight plans and the plane pretty much stays in autopilot while cruising. So, how safe is it for them to fly 300-400 passengers over the North Pole when satellite or GPS coverage is patchy if not entirely inexistent? Do DGCA norms even allow this? What is the global SOP here? If civil airliners from US or Europe regularly fly over the North Pole, surely, navigation must also not be that much of a problem.

Commercial jets have been flying across the north pole for many decades. Navigation is not a problem. These days GPS covers the whole world. Before the days of GPS, or more precise before GPS was certified for commercial aviation, they had different ways of navigating. In the very early days, planes would navigate similar to ships. Dead reckoning and using Celestial navigation techniques (e.g. using a sextant).

However, commercial jets have been equipped for decades, long before GPS, with Inertial Navigation Systems. And even today in many airliners next to radio (beacon) and GPS, they will still have INS. INS is still considered to be amongst the most reliable. Once set to a datum (a known reference point) they will drift a bit over time. But they do not rely on outside input. So there is no way anybody or anything from outside the plane can interfere with it. Submarines and in particular nuclear submarines used to (probably still do) make use of inertial navigations system. The American nuclear submarine Nautilus navigated underneath the North pole in 1958, using INS. So it’s been around for a while!

Radio, GPS and INS are all integrated into one system. The system will determine what components will give the most accurate and reliable position.

GPS does work all over the world, some systems tend to give better coverage in lower regions.

In any airspace two factor are important. You need to know your own position and you need to know the position of those around you. The first, knowing your own position is relatively simple. But to navigate safely you need to understand where everybody else is. Airspace has virtual routes and it is Air Traffic Control that ensures everybody keeps sufficient vertical and horizontal spacing.

It might come as a surprise that until recently ATC simply doesn’t know where all plane are all the time. If there was no radar coverage, they simply do not know. So for instance going across the North Atlantic, about the busiest airspace you can think of, there is no radar coverage. So there are special procedures to enter such airspaces. Essentially you need to fly very consistently a certain speed, direction and altitude. ATC figures out where everybody will be.

It is known as North Atlantic Tracks. https://en.m.wikipedia.org/wiki/North_Atlantic_Tracks For other regions there are similar systems and procedures in place.

This video explains it well, how aircraft cross the pond with no radar coverage!

https://www.youtube.com/watch?v=vBgulDeV2RU

These days with more advanced technology ATC is able to build a more granular real time picture of where everybody is. For instance ADS-B which is being rolled out currently.

https://en.wikipedia.org/wiki/Automa...211;_broadcast

ADS-B gives ATC an almost live picture of every airplane, showing speed, altitude, direction (and a bunch more).


Jeroen

[SmartCat]

I think the reason why we didn't take the polar route before is because of range issues. I think old Boeing 747s maxed out at 10,000 kms. If we look at the polar route, there doesn't seem to any major city for a stopover near the Arctic.

But now, Air India's newer 777s and 787 Dreamliners have a much bigger range (up to 15,000 kms) and can easily handle the Delhi-San Francisco polar route by flying non-stop .

The top 10 longest range airliners in the world
https://www.aerospace-technology.com...-in-the-world/

[Jeroen]

Just to add on the matter of range:

Of course, range (i.e. how far can you fly without re-fuelling) is an important criteria. But every route any aircraft flies has to take other factors into consideration. Weather obviously. But more importantly, at any point along the route would you be able to make it to a safe alternate airport, suitable to handle your particular aircraft, in case anything goes wrong.

That’s is where ETOPS comes in:

From Wikipedia:

ETOPS (/iːˈtɒps/) is an acronym used in aviation for Extended Operations. The ICAO coined the acronym for Extended Twin Operations for twin-engine aircraft operation further than one hour from a diversion airport at the one-engine inoperative cruise speed, over water or remote lands, on routes previously restricted to three- and four-engine aircraft.[1] The ICAO issues Standards and Recommended Practices (SARPS) for ETOPS, and ETOPS were extended to four-engine aircraft like the Boeing 747-8.

https://en.wikipedia.org/wiki/ETOPS

Modern planes such as the 787 operate at 3,5 hours ETOPS (i.e. they can plan to be within 3.5 hours of a suitable airport and will be able to make it there on one engine.

There are other operational parameters as well. The early 747 were limited in range due to their (lack of) fire surpassing capability. In case of a fire in the cabin, halon is released. The system needs to be able to reach a certain percentage (approx 5% halon/air) upon release and then be able to maintain a 3% halon/air mixture for a certain time. People can/will survive in such a halon/air mixture environment, but you need time to land the plane, or ensure the fire is properly put out. All that time the correct halon/air mixture must be maintained.

The early 747s fell short on the mark on this one and some re-design was needed on the fire suppression system.

Jeroen

[suresh_gs]

Originally Posted by Jeroen

This video explains it well, how aircraft cross the pond with no radar coverage!

Jeroen

Can you explain how aircraft cross the oceans without any radar coverage. Then how will the ATC track these planes.