The majority of airports around the world contend with occasional forms of inclement weather, such as thunderstorms, blizzards or hurricanes. However, there are some airports that, due to their geographical location, experience extreme weather on a regular basis. Located in sweltering deserts, frozen tundra, or towering mountain ranges, these airports provide a vital lifeline for the remote communities that depend on their service.
A perfect example of a country with greatly varying topography is China. China’s immense size provides the landscape and conditions for most forms of extreme weather. Although much of the population lives in the more temperate cities in the country’s east, the geographical range of China spreads from the mountains of Tibet into the deserts of Xinjiang and the frigid northern province of Heilongjiang.
A major criteria for success in commercial aircraft design is the versatility of performance in extreme weather environments, this versatility was a major factor in the design considerations of COMAC’s aircraft. Testing in extreme weather conditions is standard procedure for aircraft manufacturers around the world, but for COMAC this has a special meaning, as thier aircraft are not only designed in China but also for China. Of course COMAC’s aircraft are designed to be flown globally, but it is very important for the aircraft to be flown domestically. This means that COMAC engineers have to create an aircraft that can safely reach passengers in all regions of of the country. So, what are the extreme conditions that can affect commercial aircraft operations? Where are they found in China? And how has COMAC ensured its aircraft can operate safely there?
In northwestern Chinese provinces like Xinjiang and Inner Mongolia, many cities lie within the vast and barren Gobi Desert where the average temperature in cities like Turpan can rise above 119 F. Such high heat environments can present numerous challenges to an aircraft. The biggest risks posed by hot weather are reductions in aircraft performance. Aircraft rely on differences in air pressure over their wings to provide lift, with higher pressure air flowing over the bottom and lower pressure air on top. The higher the air pressure, the more efficiently the wing can generate lift. When compared with cooler air, warm air is much less dense, and as a result generates less air pressure. Within normal temperature ranges, this usually has no major impact to commercial flights. However, when temperatures climb to the extreme levels found in desert regions, the effect on aircraft performance becomes more of an issue, and can even lead to flight cancellations. For example, in 2017 an Arizona heatwave resulted in conditions “too hot to fly”, thereby forcing the Phoenix International Airport to ground over 40 flights.
Performance in hot weather was a critical component of the ARJ21’s flight testing process. In 2018, the ARJ21 demonstrated its ability to perform in extreme heat by successfully completing 12 days of testing in Turpan, where temperatures can soar as high as 119 F. Thus, the ARJ21 proved it can reach China’s hottest desert climates. Similarly, the C919 and CR929 will also undergo such testing to ensure they can serve all of China.
Extreme heat isn’t the only weather that can affect aircraft performance. On the other end of the spectrum, extreme cold can be just as much of a detriment. Some parts of China, such as the frigid northeast and portions of Inner Mongolia, can see temperatures plunging as low as -44.7 F. While aircraft are designed to regularly operate in frosty temperatures at cruising altitude, cold weather on the ground can cause a host of problems for aircraft. The first and most obvious is the issue of ice, which can easily build up on an aircraft wing resulting in dangerous drag. However, this issue is easily mitigated by de-icing procedures common in airports around the world.
Another cold weather obstacle threatening the careful choreography of flight schedules is the potential impact to aircraft systems which can lead to difficulty starting engines and other operations. Additionally, pilots have to be wary of components like brake pads freezing over, preventing the aircraft from moving on the ground. One extreme example of this problem occurred during a severe cold spell in Siberia in 2014, when temperatures plunged to -52 C, causing the brake pads on a Tupolev 134 to freeze over. In this instance, passengers had to get out of the aircraft and help push it to the runway before the flight continued normally.
While this is an extreme case, it highlights the need for the kind of cold weather testing that the ARJ21 has successfully completed throughout its testing phase, in order to ensure COMAC’s aircraft can safely reach all Chinese cities. This winter season, the Chengdu Airlines dispatched a fleet of ARJ21s to perform regular passenger services among cities in Heilongjiang Province, where they proved their real-world capability in such extreme weather.
Beyond deserts and frozen tundra, China is also host to the forbidding mountain peaks of the Himalayas. Entire regions, such as Tibet, are nestled within the valleys of some of the world’s highest mountains, which create unique challenges for the aircraft that connect them with the outside world. Beside the obvious challenges of navigating the inhospitable terrain, one of the primary challenges of mountain flying is the low pressure at altitude. The issues presented by reduced air pressure are very similar to those of flying in extreme heat, resulting in the tag “hot and high” for airports that experience a combination of these elements. However, in mountainous areas the pressure issues arise from the thinner air which provides much less lift for the wings and less oxygen for the engines than on the ground. Aircraft operating in these conditions have to cope with a loss of performance all-around, from engine thrust to wing lift. As a result, aircraft often have longer take-off rolls and climb much slower than they would at a lower altitude. When combined with high mountains on either side, these areas are truly some of the most difficult regions for operation.
Ensuring that Chinese aircraft can safely service mountainous regions is a critical component to nationwide operations. A prime example of flight testing in such conditions can be seen in China’s earliest large passenger aircraft project, the Shanghai Y-10. In 1981, the Y-10, a large four-engine airliner traveled to the city of Lhasa, located 11,713 feet above sea level on multiple occasions. Braving the high altitude and rugged mountain peaks, the Y-10 proved that Chinese aircraft could successfully operate from the most forbidding mountain regions.
While you are most likely to visit a large coastal city on your next trip to China, keep in mind that what you are seeing is only a fraction of China’s diverse landscapes and cultures. Although each of China’s extreme regions provides unique challenges to aircraft operating into them, you can be assured that in the near future, even they will be regularly visited by homegrown aircraft.