Airline route planning and operational changes are complex but interesting areas. Some passengers will follow this closely, fascinated where the flight is taking them, while others barely notice. If you do follow routes, though, one thing you will see on long-haul flights to Asia is that they never fly over the Tibet Autonomous Region.
Few aircraft over Tibet
The region in question is the Tibet Autonomous Region in China. This is a sparsely populated and mountainous area, also known as the Tibetan plateau – a meaningful name given that the average elevation in the region is over 4,500 meters.
With it being sparsely populated, there are few flights to or within the region (the whole region only accounts for 0.2% of China’s population, to put it in context). There are international airports in Lhasa and Xining, and plenty of flights now operate to China and regionally. But airlines flying to or from other destinations will avoid the region entirely, despite it often being the most direct route.
Take a look at this image from RadarBox.com showing the airports in the region. You will note the whole region is empty of flights, with several aircraft tracking just above and below.
Likewise, if you consider a flight path for a flight from Europe to China (this is BA31 from London to Hong Kong), you will see how it routes around the area.
So why does do airlines do this? There are three main reasons (these are explained more fully in this interesting video from RealLifeLore).
Not able to descend to a safe altitude in an emergency
The leading reason for aircraft avoiding the region is the high average height of the terrain. This is over 14,000 feet. Aircraft, of course, cruise much higher than this. But the procedure in the event of an emergency such as cabin depressurization is to descend to 10,000 feet before diverting to an airport.
With terrain this high, the aircraft would not be able to descend sufficiently. There is, of course, oxygen provided for passengers. But this is a limited supply and based on the assumption that the aircraft will quickly reach a safe altitude. To make the situation worse, there are few diversion airports, and these could be a long flight from some parts of the region.
Risk of increased turbulence
Turbulence during a flight is caused by air currents moving up and down in ripples and at different speeds. This is impacted by several factors, including the sun’s heating effect, weather conditions – and mountains. Air currents will rise over mountains, creating disrupting flows.
Turbulence can happen on any route – as we have all experienced. But in this high mountainous region, it is more likely and could be hard to avoid. This would be disrupting for passengers and also could make an emergency situation even more dangerous.
Risk of jet fuel freezing
And not surprisingly, the final reason is also linked to the mountainous terrain. Temperatures are much lower, which leads to a risk the jet fuel could freeze. Standard Jet A1 fuel has a freezing point of -47 degrees Celsius (and Jet A, which is more common in the US, is slightly higher at -40 degrees).
Such temperatures are rarely reached, especially for prolonged periods of time. But at altitude over the already cold mountains, there is an increased risk of this. It is not a significant problem for shorter flights in or out of the region, but a sustained long flight over the area could be different.
Have you flown in the Tibetan region? Or would you like to discuss any other airline routing facts? Let us know in the comments.