Sunday, September 12, 2021

Why airplanes don’t fly over Tibet?

You must have heard on social media platforms that there is a region called Tibet where airplanes do not fly over. Some people relate it with some supernatural power and other nonsense stuff which is totally wrong.

There is some scientific and technical reasons why airplanes are not allowed to fly over this region of Asia. Do you know why airplanes don’t fly over Tibet? Well there are a lot of reasons behind it. Let us have a look at some of them. 

Mountain height

Tibet which is also known the ‘Roof of the World’ due to its towering Himalayan peaks, makes it impossible for airplanes to fly over. The Tibet plateau is surrounded by the extensive mountain ranges of Himalaya.

It is bounded in the north by a broad escarpment where within few hundreds of kilometer the altitude drops from around 16,000 ft to 5,000 ft. The mountain height is one of the major reason why airplanes are not advised to fly over this region.

Required oxygen level

The second reason is the required oxygen level in case of emergency. What does it mean? Let us have a look. Consider a situation when there’s a loss of cabin pressure, and the airplane is supposed to descend to an altitude where there’s enough air to breathe. We know that the maximum altitude for the average human being to breathe normally is less than about 12,000 ft.

In most of the airplanes, during an emergency descent, passenger oxygen only lasts for a few minutes, and if such an emergency condition arises in the region above Tibet then it would not be possible to descend to an altitude below 12,000 ft as the average height of mountains in this region is very high. This is the reason why airplanes are avoided to fly over this region.

Drift Down

Drift Down is basically the maximum thrust or the minimum rate descent required by an engine failure in a multi-engine aircraft during climb or during cruise when an aircraft cannot maintain its current altitude.

Consider a situation in which a passenger aircraft loses one of its engines for any reason. Even after engine failure it is still able to safely fly but it can no longer fly at a very high altitude. Thus it needs to drift down to a lower altitude where it can then maintain a safe and stable flight despite engine failure.

The pilots and the airline dispatchers are provided the “drift down procedures to a predetermined altitude due to engine failure” and “the gross weights”. Using these procedures airplanes can be safely descended to a lower height. In mountain areas, this safe prescribed height would sometimes be lower than the mountain peaks. Thus it is unfavourable to fly over regions having very high mountain peaks like the Tibet plateau! 

Clear air turbulence over the peaks

Clear air turbulence is the turbulence that we can’t see rather it is related to jet streams. Disruption of airflow created by the mountain creates eddies, which if we fly through can be very turbulent. The only prediction tool for clear air turbulence is the experience of other aircrafts, which isn’t that much in the Tibetan Plateau. 

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