Why a dog-leg flightpath HKG to LHR?
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Why a dog-leg flightpath HKG to LHR?
I flew SLF on the 2335 VAA flight 201 from HKG to LHR on 5 Feb 2015 (yesterday), and was curious about the flight path.
According to the in-seat skymap, after take-off the A340 flew on a heading of around 315 for a short while, then turned right onto a heading of about 350 for about an hour, and only then turned left to pick up a great circle route direct to LHR.
So I was wondering if the reason for the dog-leg was either:
1. Avoiding bad weather or
2. acquiring a tail wind or
3. avoiding Ukrainian airspace or
4. something else!
Any thoughts?
According to the in-seat skymap, after take-off the A340 flew on a heading of around 315 for a short while, then turned right onto a heading of about 350 for about an hour, and only then turned left to pick up a great circle route direct to LHR.
So I was wondering if the reason for the dog-leg was either:
1. Avoiding bad weather or
2. acquiring a tail wind or
3. avoiding Ukrainian airspace or
4. something else!
Any thoughts?
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I was told that Chinese airspace was quite restricted. Only a few authorised tracks for international flights.
I had asked why my Shanghai - London flight practically overflew Beijing.
I had asked why my Shanghai - London flight practically overflew Beijing.
Last edited by ExXB; 8th Feb 2015 at 11:28. Reason: typo
I was told that Chinese airspace was quite restricted. Only a few authorised tracks for international flights.
In quite a few parts of the world access to routes are regulated by various agreements and treaties, but Chinese airspace in particular is very rigidly controlled, to the extent that it can sometimes be difficult, (and in the past was almost impossible) to even negotiate a few tens of miles/kilometres lateral deviation from an airway centreline to get around thunderstorms. There's also only a limited number of routes across Mongolia and also a limited number of places where Russian ATC will accept entry into their airspace.
FWIW there is sometimes the option of a route that passes in the vicinity of Lanzhou and then eventually heads west to Urumqi - that's certainly a route that I've seen used going eastbound.
If you try routing much further south and west you will eventually run into problems with overflying significantly high terrain for an extended period of time (the "what if's" come into play: e.g. engine out performance, sufficient availability pass/crew oxygen in the event of a decompression).
Last edited by wiggy; 8th Feb 2015 at 20:16.
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I thank you for that comprehensive response, it hadn't occurred to me (obviously) that there might in this case be artificial routing restrictions (as opposed to those imposed by natural phenomena).
... flew on a heading of around 315 for a short while, then turned right onto a heading of about 350 for about an hour, and only then turned left to pick up a great circle route direct to LHR.
Last edited by WHBM; 13th Feb 2015 at 16:54.
I was on a flight from Los Angeles to Bangkok. We were tracking south over Kamchatka directly towards Beijing. Once in Chinese airspace, we made a complete semi-circle to the west of Beijing, before picking up our southerly track again.
Airlines would like to fly great circle tracks as this is the shortest distance between two points, unfortunately it's seldom possible. Prevailing winds, overflight clearances, staying within range of diversionary airports, required air traffic control routings etc all ensure that less direct routings are the norm.
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Airlines actually prefer minimum time tracks which may be longer in distance than a great circle route. The shorter the time in the air, the less the cost and the better the punctuality. Distance flown is less important than time in the air and, for any given long haul flight, the most efficient route is a minimum time track where wind, weather, en route restrictions and distance from diversion airfields are all calculated to give the most efficient route which is often very different to simple great circle.
The shortest distance between two points is a straight line i.e. a great circle track. The shortest distance will normally result in flying for the least time to cover that distance which will result in the minimum time in the air. As I stated, other factors come into play which may make it more economical to fly a less direct route. Airlines have departments devoted to flight planning and take all these factors into account to come up with the most economical route.
The minimum time in the air may not result in the lowest cost if heavy overflight charges are involved, it may be cheaper to spend a little longer in the air and fly around. North Korea charges very expensive fees to overfly the country, airlines decide whether to pay or take an alternative route.
The cost of operating the aircraft also comes into play, if fuel is cheap as it is at the moment then extra flying time costs less. The hourly lease rate varies among aircraft as well, it may be cheaper to speed up and use more fuel or slow down and use less fuel. If fuel is expensive and there is a tailwind it may be more economical to reduce cruise speed and ride the wind. Crew flight time limits are also a consideration, if a return flight with the same crew is required then it may be cheaper to fly fast to stay within limits, if a night stop is involved timing is less critical.
Minimum time may not necessarily result in the minimum cost.
The minimum time in the air may not result in the lowest cost if heavy overflight charges are involved, it may be cheaper to spend a little longer in the air and fly around. North Korea charges very expensive fees to overfly the country, airlines decide whether to pay or take an alternative route.
The cost of operating the aircraft also comes into play, if fuel is cheap as it is at the moment then extra flying time costs less. The hourly lease rate varies among aircraft as well, it may be cheaper to speed up and use more fuel or slow down and use less fuel. If fuel is expensive and there is a tailwind it may be more economical to reduce cruise speed and ride the wind. Crew flight time limits are also a consideration, if a return flight with the same crew is required then it may be cheaper to fly fast to stay within limits, if a night stop is involved timing is less critical.
Minimum time may not necessarily result in the minimum cost.
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Metro man, I suggest you follow one of the flight tracking programs on the internet and see how few long haul flights follow great circle routes. On the north Atlantic the tracks are designated east and westbound each day. They rarely correspond to great circles between any points in Europe and the USA. The same goes for the south Atlantic to Brazil and Argentina. The likelihood of US ATC offering great circle routings, even under Free Flight, is unusual.
On the Pacific between Australia and New Zealand the routes change, sometimes minimally, on a daily basis.
The components you list which determine routes chosen are all valid but in over fifty years of listening to HF broadcasts, in over thirty years of flying long haul as a passenger and closely following routes taken, and years of organising professional conferences for ATC management worldwide at which route planning was regularly discussed, I have only rarely come across flights operating a true great circle route.
Minimum time tracks are used to minimise flight time for passengers, for airframe and engines and, using advantageous winds, to save fuel and have become the industry standard.
On the Pacific between Australia and New Zealand the routes change, sometimes minimally, on a daily basis.
The components you list which determine routes chosen are all valid but in over fifty years of listening to HF broadcasts, in over thirty years of flying long haul as a passenger and closely following routes taken, and years of organising professional conferences for ATC management worldwide at which route planning was regularly discussed, I have only rarely come across flights operating a true great circle route.
Minimum time tracks are used to minimise flight time for passengers, for airframe and engines and, using advantageous winds, to save fuel and have become the industry standard.
Airlines may not follow great circle tracks for the reasons I listed. North Atlantic tracks are designed to accommodate the huge number of aircraft flying between Europe and North America. With no radar monitoring possible, separation has be be greater. Only a certain number of aircraft can be on a track at a particular time therefore a number of different routes have to be drawn up and aircraft have to comply with minimum navigation performance standards. The tracks chosen take wind into account which obviously differs from day to day.
Free flight is simply not possible with the ATC system at the moment, aircraft have to follow specific departure, enroute and arrival procedures for seperation to be maintained. With advances in technology, free flight may be the norm in a few decades time.
On the Pacific ETOPS comes into play and routing may differ depending on the airlines approval time or weather conditions which render an ETOPS alternate unsuitable during the required time period.
Singapore Airlines had a number of widely differing routes on their business class A340 service to New York and chose the best one for the day.
Auckland to London gives the choice of going east or west, Air New Zealand are a true around e world airline.
I have nearly thirty years of flying as a pilot rather than a passenger.
Free flight is simply not possible with the ATC system at the moment, aircraft have to follow specific departure, enroute and arrival procedures for seperation to be maintained. With advances in technology, free flight may be the norm in a few decades time.
On the Pacific ETOPS comes into play and routing may differ depending on the airlines approval time or weather conditions which render an ETOPS alternate unsuitable during the required time period.
Singapore Airlines had a number of widely differing routes on their business class A340 service to New York and chose the best one for the day.
Auckland to London gives the choice of going east or west, Air New Zealand are a true around e world airline.
I have nearly thirty years of flying as a pilot rather than a passenger.
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Metro man, I think we are singing from the same hymn sheet but in different keys. I may not be a pilot but designing conferences for ATC, as well as other airline related topics, brought me into detailed contact with all levels from controllers to Directors General of ATC, from airline route planners, through pilots to airline CEOs.
I got the impression from the airlines that, given all the factors we have discussed, minimum time tracks were the most cost effective method of flying between long haul points using current technologies.
With regard to the North Atlantic tracks, I have spent time at Shanwick's Ballygirreen facility and worked closely with its Prestwick arm on conference topic planning concerning FANS.
The track system was designed as you state but the development of TCAS, dependable INS and ETOPs has, over the years, led to the introduction of RVSM, (which is now universal at altitude) and the number of random track clearances on the Atlantic has significantly increased. The current track system is almost totally weather driven to give the fastest crossing times.
Regarding Free Flight, I used to own and organise an ATC conference held in London. This was open to directors and senior managers of ATC, ATC equipment manufacturers and airline directors and was sponsored by major manufacturers and endorsed by the UK CAA and the FAA . In December 1995 at the Edwardian Hotel, Heathrow, L Lane Speck of the FAA announced to what can only be described as a disbelieving audience the results of David Hinson's FAA task force's report into Free Flight in US airspace and the planned implementation of the system, starting between FL360 and FL450 with a target of all airspace down to FL010 by 2002 and then down to 5000 feet outside terminal areas.
I was asked to design and organise a series of seminars to be held around the US and in March 1997 went to Washington to present my proposal. Prior to 9/11 I had jump seat privileges with a number of airlines and discussed Free Flight with a number of crews between 1996 and 1999. Few, had heard anything about it, the proposed timetable or the implementation of Stage One.
The seminars never took place and the implementation of Stage One was limited. Many reasons have been cited ranging from budget cuts by the Clinton administration through to opposition from the general aviation lobby which had concerns regarding the cost of mandatory equipment and the implementation of what they saw as an increase in regulation.
Since I retired, Free Flight has become Next Gen ATC in the US and is slowly being implemented. Dallas went live in November 2014 for instance. In Europe Gate to Gate 4D Trajectory Management is under intensive development. Both systems work on the basis of minimum time in the air.
Airlines see the benefits of shorter journey times, greater punctuality and savings in fuel and maintenance. Great circle routes may well have more usage under the new systems but the systems have been simulated on the basis of minimum time tracks taking into account weather, terrain and other variables.
I got the impression from the airlines that, given all the factors we have discussed, minimum time tracks were the most cost effective method of flying between long haul points using current technologies.
With regard to the North Atlantic tracks, I have spent time at Shanwick's Ballygirreen facility and worked closely with its Prestwick arm on conference topic planning concerning FANS.
The track system was designed as you state but the development of TCAS, dependable INS and ETOPs has, over the years, led to the introduction of RVSM, (which is now universal at altitude) and the number of random track clearances on the Atlantic has significantly increased. The current track system is almost totally weather driven to give the fastest crossing times.
Regarding Free Flight, I used to own and organise an ATC conference held in London. This was open to directors and senior managers of ATC, ATC equipment manufacturers and airline directors and was sponsored by major manufacturers and endorsed by the UK CAA and the FAA . In December 1995 at the Edwardian Hotel, Heathrow, L Lane Speck of the FAA announced to what can only be described as a disbelieving audience the results of David Hinson's FAA task force's report into Free Flight in US airspace and the planned implementation of the system, starting between FL360 and FL450 with a target of all airspace down to FL010 by 2002 and then down to 5000 feet outside terminal areas.
I was asked to design and organise a series of seminars to be held around the US and in March 1997 went to Washington to present my proposal. Prior to 9/11 I had jump seat privileges with a number of airlines and discussed Free Flight with a number of crews between 1996 and 1999. Few, had heard anything about it, the proposed timetable or the implementation of Stage One.
The seminars never took place and the implementation of Stage One was limited. Many reasons have been cited ranging from budget cuts by the Clinton administration through to opposition from the general aviation lobby which had concerns regarding the cost of mandatory equipment and the implementation of what they saw as an increase in regulation.
Since I retired, Free Flight has become Next Gen ATC in the US and is slowly being implemented. Dallas went live in November 2014 for instance. In Europe Gate to Gate 4D Trajectory Management is under intensive development. Both systems work on the basis of minimum time in the air.
Airlines see the benefits of shorter journey times, greater punctuality and savings in fuel and maintenance. Great circle routes may well have more usage under the new systems but the systems have been simulated on the basis of minimum time tracks taking into account weather, terrain and other variables.
