MUMBAI: Lima 639 and Lima 301 might sound like gobbledygook to most Indians, but these are the two air routes that along with the Ahmedabad and Mumbai air traffic control form the foursome that come to the rescue when Pakistan closes its airspace to India.
Since April 24, over 130 westbound international flights taking off daily from northern and eastern airports such as Delhi, Amritsar, Chandigarh, Lucknow, Jaipur, Kolkata are being re-routed south where the Ahmedabad and Mumbai air traffic control assign them altitudes and put them onto L639 or L301 to overfly the Arabian sea and reach the Muscat airspace. Once there, they turn north to overfly Iran and complete the detour. In normal times, these flights after taking-off, turn west to cross over to Pakistan and show up on the radars of Lahore or Karachi air traffic control before they move into Iran.
“Every time Pakistan shuts down its air space, Mumbai air traffic control gets a rush of re-routed flights overflying from north and east India. It happened in 1971 (Indo-Pak war), 1999 (Kargil conflict), 2001-2002 (post Parliament attack), 2019 (post Balakot airstrikes) and now post the Pahalgam terror attack,” said a retired air traffic controller. This time around, Mumbai air traffic control has been handling about 130 re-routed flights per day, while Ahmedabad handles about 80 affected flights, passing most of them over to Mumbai. These flights bunch up during peak hour, leading to dense traffic at certain times of the day such as 9.30 pm to 11 pm and 2 am to 3.30 am.
The 2019 airspace closure was the most challenging one, overnight about 500 flights rerouted south and showed up in the airspace controlled by the Mumbai air traffic control. “All countries stopped using the Pakistan airspace. The current load is comparatively lighter with only about 130 additional rerouted flights, mostly belonging to Indian carriers,” he added.
“The load was immediate and immense, too heavy for the then existent air routes to handle,” he said. The air route L639 was established, born out of necessity, during the 2019 Pak airspace closure. Of the six routes taken by flights from Mumbai to Muscat airspace, L639 is the most popular. “Since the rerouted flights come from the north, they try to catch the first available route to the west without overflying the Pak airspace and that’s L639,” he said.
L639 starts overhead Bhopal , links to Ahmedabad, Mundra, overflies the Arabian sea to end at a way point (a navigational checkpoint at a specific location in space) called “RASKI”, near Muscat. L301, runs about 150 nm south of L639 and converges at RASKI. Along these two air routes, traffic has been dense following the Pak airspace closure. Aircraft flying west__ from India to US, Europe, that is__ are assigned even-numbered altitudes and they cruise at 30,000 feet, 32,000 feet, 34,000 feet etc up to about 42,000 feet. Aircraft flying from west to east into India are put on odd-numbered flight levels such as 29,000 feet, 31,000, 33,000 feet etc. Then again, along each flight level or altitude on L639 and L301, aircraft are lined up one behind the other, separated by 20 nm (37 km).
Along most other air routes that fly over the sea, a horizontal separation of 50 nm is maintained between aircraft flying on a given flight level. But in the past few years, the Mumbai air traffic control, in a providential move, put procedures and practises in place that has enabled them to reduce the horizontal separation on L639 and L301. In Jan trials were complete, and L639, L301 became the first two air routes in Asia Pacific to afford a reduced horizontal separation of 20 nm. “With the reduced separation, more aircraft can be accommodated on each altitude,” he added. But the traffic density has been so high on these two routes that flights going from Mumbai to places like Shamshabad, Pune, Nagpur, Kolkata are being put on routes that are 50 nm or 100 nm south of L301, so these flights have been indirectly hit by the closure, he added.
In the world of air transportation, permitting a foreign airline’s flight to overfly your country’s airspace is the most basic of the privileges one country can grant another. The UN’s International Civil Aviation Organisation (ICAO) terms it the `First Freedom Right’. These involve only overflying flights. They cruise at over 29,000 feet and don’t land in the country where they have only the first freedom right. These overflying flights are handled by the `en route controller’. Mumbai’s enroute control normally handles about 2500 overflying flights in 24 hours. Mumbai had five frequencies or sector on which overflying flights contact the enroute controller. For instance: pilots of flights coming from north tune into 132.7 MHz to speak to the en route controller.
The en route controllers of Mumbai and Ahmedabad then are the officials ensuring the traffic continues to flow from India to the west. The Ahmedabad air traffic control is part of what’s called the ‘Mumbai FIR’ or Flight Information Region. It’s essentially a defined airspace that is manned by the Mumbai air traffic control. All airspace in the world is divided into FIRs. India has five FIRs with the Mumbai FIR covering airspace over Gujarat, Maharashtra, and a large swathe of the Arabian sea. The entire backend operation of handling the flights re-routed due to Pak airspace closure then is handled by the Mumbai FIR.
What is the impact on airlines and is there an impact on the climate?
With airlines flying longer routes to circumvent the Pak airspace, the fuel burn is more and so are the carbon emissions. A Delhi-New York B777 flight overflying Pak airspace typically burns about 106,500 kg of fuel. While that adds to the cost, the other side-effect because of the higher fuel consumption is increased carbon emissions. For the said 106,500 kg of fuel the aircraft emits about 336 metric tons of carbon dioxide. But a re-routed B777 flight that avoids Pak airspace, takes the L639 route, does a refuelling halt in Vienna, burns about 125,500 kg of fuel, which is roughly 396 metric tons of carbon dioxide. (these are rough estimates, wind speed, direction, routing etc affect these numbers).
Since April 24, over 130 westbound international flights taking off daily from northern and eastern airports such as Delhi, Amritsar, Chandigarh, Lucknow, Jaipur, Kolkata are being re-routed south where the Ahmedabad and Mumbai air traffic control assign them altitudes and put them onto L639 or L301 to overfly the Arabian sea and reach the Muscat airspace. Once there, they turn north to overfly Iran and complete the detour. In normal times, these flights after taking-off, turn west to cross over to Pakistan and show up on the radars of Lahore or Karachi air traffic control before they move into Iran.
“Every time Pakistan shuts down its air space, Mumbai air traffic control gets a rush of re-routed flights overflying from north and east India. It happened in 1971 (Indo-Pak war), 1999 (Kargil conflict), 2001-2002 (post Parliament attack), 2019 (post Balakot airstrikes) and now post the Pahalgam terror attack,” said a retired air traffic controller. This time around, Mumbai air traffic control has been handling about 130 re-routed flights per day, while Ahmedabad handles about 80 affected flights, passing most of them over to Mumbai. These flights bunch up during peak hour, leading to dense traffic at certain times of the day such as 9.30 pm to 11 pm and 2 am to 3.30 am.
The 2019 airspace closure was the most challenging one, overnight about 500 flights rerouted south and showed up in the airspace controlled by the Mumbai air traffic control. “All countries stopped using the Pakistan airspace. The current load is comparatively lighter with only about 130 additional rerouted flights, mostly belonging to Indian carriers,” he added.
“The load was immediate and immense, too heavy for the then existent air routes to handle,” he said. The air route L639 was established, born out of necessity, during the 2019 Pak airspace closure. Of the six routes taken by flights from Mumbai to Muscat airspace, L639 is the most popular. “Since the rerouted flights come from the north, they try to catch the first available route to the west without overflying the Pak airspace and that’s L639,” he said.
L639 starts overhead Bhopal , links to Ahmedabad, Mundra, overflies the Arabian sea to end at a way point (a navigational checkpoint at a specific location in space) called “RASKI”, near Muscat. L301, runs about 150 nm south of L639 and converges at RASKI. Along these two air routes, traffic has been dense following the Pak airspace closure. Aircraft flying west__ from India to US, Europe, that is__ are assigned even-numbered altitudes and they cruise at 30,000 feet, 32,000 feet, 34,000 feet etc up to about 42,000 feet. Aircraft flying from west to east into India are put on odd-numbered flight levels such as 29,000 feet, 31,000, 33,000 feet etc. Then again, along each flight level or altitude on L639 and L301, aircraft are lined up one behind the other, separated by 20 nm (37 km).
Along most other air routes that fly over the sea, a horizontal separation of 50 nm is maintained between aircraft flying on a given flight level. But in the past few years, the Mumbai air traffic control, in a providential move, put procedures and practises in place that has enabled them to reduce the horizontal separation on L639 and L301. In Jan trials were complete, and L639, L301 became the first two air routes in Asia Pacific to afford a reduced horizontal separation of 20 nm. “With the reduced separation, more aircraft can be accommodated on each altitude,” he added. But the traffic density has been so high on these two routes that flights going from Mumbai to places like Shamshabad, Pune, Nagpur, Kolkata are being put on routes that are 50 nm or 100 nm south of L301, so these flights have been indirectly hit by the closure, he added.
In the world of air transportation, permitting a foreign airline’s flight to overfly your country’s airspace is the most basic of the privileges one country can grant another. The UN’s International Civil Aviation Organisation (ICAO) terms it the `First Freedom Right’. These involve only overflying flights. They cruise at over 29,000 feet and don’t land in the country where they have only the first freedom right. These overflying flights are handled by the `en route controller’. Mumbai’s enroute control normally handles about 2500 overflying flights in 24 hours. Mumbai had five frequencies or sector on which overflying flights contact the enroute controller. For instance: pilots of flights coming from north tune into 132.7 MHz to speak to the en route controller.
The en route controllers of Mumbai and Ahmedabad then are the officials ensuring the traffic continues to flow from India to the west. The Ahmedabad air traffic control is part of what’s called the ‘Mumbai FIR’ or Flight Information Region. It’s essentially a defined airspace that is manned by the Mumbai air traffic control. All airspace in the world is divided into FIRs. India has five FIRs with the Mumbai FIR covering airspace over Gujarat, Maharashtra, and a large swathe of the Arabian sea. The entire backend operation of handling the flights re-routed due to Pak airspace closure then is handled by the Mumbai FIR.
What is the impact on airlines and is there an impact on the climate?
With airlines flying longer routes to circumvent the Pak airspace, the fuel burn is more and so are the carbon emissions. A Delhi-New York B777 flight overflying Pak airspace typically burns about 106,500 kg of fuel. While that adds to the cost, the other side-effect because of the higher fuel consumption is increased carbon emissions. For the said 106,500 kg of fuel the aircraft emits about 336 metric tons of carbon dioxide. But a re-routed B777 flight that avoids Pak airspace, takes the L639 route, does a refuelling halt in Vienna, burns about 125,500 kg of fuel, which is roughly 396 metric tons of carbon dioxide. (these are rough estimates, wind speed, direction, routing etc affect these numbers).
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