On Thursday, 6 July we tracked the highest number of commercial flights ever, following more than 134,000. We posted the map below the following day to illustrate the busy skies and we received numerous questions about the blank areas on the map. Why are there big holes in places around the world? //

Ukraine... //

On the map above, blue pins represent airports while the white and yellow lines represent available airways that aircraft can use to transit an area. Nearly all of Tibet is airway-free, but not because the terrain is too high to fly over. Even the tallest mountains in the world just to the southwest are easily traversed, however, safety is again the prime consideration. Aircraft operating at a normal cruising altitude of 35-40,000 feet are flying through air that is less dense and contains less oxygen than air lower in the atmosphere.

At cruising altitude there is only about a minute of useful oxygen available before Hypoxia can begin affecting the brain. This is why airplanes are equipped with oxygen masks and why aircraft descend to 10,000 feet or lower in the event of a depressurization. The problem in Tibet is that much of the plateau is at or above 10,000 feet above mean sea level, making it impossible to descend to a safe altitude. Aircraft that do operate in this area follow special procedures and carry extra equipment to mitigate an emergency situation. For nearly all others, flying around is the easiest thing to do.