#5 The Map
Here is the map showing the plane routes for the Asia for a given calendar. As you can see, most of the planes are not seen flying over the region of Tibet.. Here is why!
The reasons for this are..
As already said, Big Foot cannot fly so don't worry! :P

#4 The Altitude
The average height of the ground level here is 16000 ft. above the sea level.. So, if in any case you had to make an emergency landing, it would be highly impossible in the first place and..
Though you land, no one can inhale as humans can only inhale oxygen only below 12000 ft.above the sea level!!
This means, emergency landing wold be a suicide..

#3 Radar
Yes, at this heights, there are lesser wirelines and so, they offer very poor communications...
The radar services are literally not possible in here..
That means, if the pilot had to ask something or say something.. There won't be a microphone in his hand..
Keep going for more infromation!!

#2 No Circle route
Also, the major reason is that there are no circle routes through here that are beneficial.. That means, there is no much traffic covering many cities and places passing thorugh Tibet
Though some Russian & Chinese airlines do fly over this region now and then, the number of flights are very very low..
You can testify this fact by visiting a library with a 3D globe, take a thread or a string to see how many major destinations fall directly through the Tibet region. Shockingly, there are very few. In fact, Heathrow airport, which is one of the largest in the world, only has four routes that fly over Tibet.

#1 Not India directly
One other reason which counts is that all the polar routes from North America do not fly to Asia through India directly first. This is because India is out of range for most of the aircraft..
So most of the European, American flights entering Asia go through Dubai as that way it is faster and cheaper and it is DUBAI !!!
These are the reasons why Tibet is untouched by flights all over the world!!