[강갑생의 바퀴와 날개] A passenger plane flying 10,000m above the Himalayas, 8,000m

Airliners fly at a height of about 9000 to 13,000 m. It is said to set an appropriate altitude in consideration of route distance, wind by altitude, or outside temperature. Anyway, at this altitude, it seems that you can fly freely anywhere in the world.

However, if you look at route information around the world, you can see that there are few routes only around the Himalayas. Rarely, there is a crossing route that crosses the Himalayas, but there is no final route flying along the mountain range. If there is a longitudinal route, the Himalayan Mountains looking down through the window of an airplane would be spectacular.

Routes are usually established in consultation with the World Civil Aviation Organization (ICAO) and the countries concerned. At this time, many factors such as economic and diplomatic factors and safety are considered. So, what is the reason that there are so few routes over the Himalayas?

When I inquired with Asiana Airlines and Korean Air, which operate mid- to long-haul routes, the answer was “because it is difficult to cope with an emergency situation.” The Himalayas is a huge mountain range with 14 peaks over 8000m, including Everest (8848), the world’s highest peak.

However, the flight altitude of airliners is generally more than 1000m higher than Everest. It means that the height of the peak is not a situation that will impede flight safety. The problem is emergency response when the pressurization of the gas is lost due to various reasons.

Pressurization refers to the use of a compressor to increase the in-flight pressure of an aircraft flying at high altitude, allowing the occupants to breathe normally. Normally, the pressurization pressure in the cabin is about 2440m (8000ft). This is the pressure between the peaks of Mt. Baekdu (2744m) and Mt. Halla (1947m).

If there is an abnormality in pressurization, it becomes difficult for passengers to breathe right away. When this happens, the emergency oxygen mask installed on the shelf comes down first. And the plane descends to an altitude of 3000m so that passengers can breathe without an oxygen mask.

When flying over sea or flat land, you can lower the altitude to the shortest distance from anywhere. But in the Himalayas it is virtually impossible to descend below 3000m due to the high peaks. This is because not only 8000m but also 6000~7000m peaks are rising.

Of course, you can also get out of the Himalayas and go to a place where you can descend up to 3000m. According to Asiana Airlines, oxygen masks used by passengers supply oxygen for 15 to 20 minutes depending on the model.

For reference, the B777 and A330 operated by Asiana Airlines are supplied with oxygen for about 22 minutes, and the A321 is said to take about 15 minutes. Also, the oxygen mask used by pilots and other flight attendants lasts about 2 hours.

Considering the flight speed of 900 km/h here, theoretically, it can be considered as a possible time to hurry out of the danger zone. However, if other reasons overlap and it is difficult to escape from the danger zone and descent is the only solution, it would be difficult to get rid of frustration.

For this reason, airlines explain that it is not necessary to open a route over the Himalayas, even at risk. Airlines apply what is called a’alpine avoidance procedure’ when flying routes that pass through high altitude areas, even if not as high as the Himalayas.

Based on Incheon Airport, routes include Istanbul (Turkey), Almaty (Kazakhstan), and Tashkent (Uzbekistan). When operating these routes, if a loss of pressurization occurs, you must follow an evasion route that goes down 3000m or less, avoiding high obstacles.

At this time, since it is not descending to the shortest distance, the flight time is longer and more oxygen is required than the amount of oxygen prepared in general. So it is said that passenger planes operating these routes are loaded with more oxygen than usual. It is impressive that it really takes a lot of consideration and preparation to fly safely.

Gap-saeng Kang, traffic reporter [email protected]