你经历过飞机备降吗？
Have you ever experienced alternate landing?
飞机在空中飞行的过程中，偶尔会遇到航路交通管制、天气恶劣、机械故障等因素，导致飞机不能到达目的地机场，而要飞往其他机场。
In the process of air flight, the aircraft will occasionally encounter factors such as route traffic control, bad weather, mechanical failure, etc., resulting in the aircraft being unable to reach the destination airport and flying to other airports.
这个过程就是备降。
This process is called alternate landing.
引起备降的原因不同，飞行员需要结合当时的具体情况和飞机状态来综合判断，前往哪一个机场备降更合适。
The reasons for alternate landing are different. The pilot needs to make a comprehensive judgment based on the specific situation and aircraft status at that time to determine which airport is more suitable for alternate landing.
比如，飞机的机型大小、重量不同，对机场跑道的要求不同。一些大型的飞机无法在级别较低的跑道降落。
For example, the size and weight of aircraft are different, and the requirements for airport runway are different. Some large aircraft cannot land on runways with lower grades.
所以即便机组发现飞机出现突发情况需要备降，也不一定会选择当时距离最近的机场降落。
So even if the crew finds that the aircraft needs to alternate in case of emergency, they may not choose the nearest airport to land at that time.
另外，当发生恶劣天气时，原定备降机场距离航路较近，很可能也正在受到恶劣天气的影响。比如北京飞上海浦东的航班，在途中得知浦东机场天气恶劣。原计划的备降机场是上海虹桥机场。但是虹桥机场距离浦东机场非常近，很有可能也正在遭受恶劣天气。即便天气良好，可能已经有大量航班选择在虹桥机场备降，已经或即将出现航路拥堵的情况。这个时候，像虹桥机场这样的临近机场就不一定是航班备降的最佳选择了。
In addition, when bad weather occurs, the original alternate airport is relatively close to the route, and is likely to be affected by bad weather. For example, on the flight from Beijing to Shanghai Pudong, I learned that the weather at Pudong Airport was bad. The planned alternate airport is Shanghai Hongqiao Airport. However, Hongqiao Airport is very close to Pudong Airport, and it is likely that it is also suffering from bad weather. Even if the weather is good, there may have been a large number of flights choosing to alternate at Hongqiao Airport, and the route congestion has occurred or is about to occur. At this time, neighboring airports like Hongqiao Airport are not necessarily the best choice for alternate flights.
机组可能会根据飞机剩余油量，确认临近机场的天气和航路情况后，再制定备降方案。
The crew may determine the weather and route conditions of the airport according to the aircraft's remaining fuel, and then formulate an alternate landing plan.
此外，因为机械原因造成飞机不宜再飞往目的地机场降落时，需要考量的因素更多。
In addition, more factors need to be considered when the aircraft is no longer suitable to fly to the destination airport for landing due to mechanical reasons.
飞机故障对飞机飞行的影响大小不同，机组考量备降方案的侧重点也不同。
The impact of aircraft failure on aircraft flight is different, and the focus of the crew's consideration of alternate landing plan is also different.
比如，一家以北京为运营和维修基地的飞机从哈尔滨起飞，原计划经停天津后，飞往北京。但是，飞机在临近天津上空时，发现飞机的自动驾驶系统出现故障。此时飞机应该立刻落地天津吗？其实，机组经过综合判断，决定将飞机直接飞往北京后再落地。
For example, an aircraft with Beijing as its operation and maintenance base took off from Harbin and was originally scheduled to fly to Beijing after stopping in Tianjin. However, when the aircraft was approaching Tianjin, it was found that the auto drive system system of the aircraft was faulty. Should the plane land in Tianjin immediately? In fact, after comprehensive judgment, the crew decided to fly directly to Beijing before landing.
首先，飞机油量充足，完全可以飞往北京。其次，航司运营和维修基地在北京，飞往北京可以尽快得到维修，保障该航司后续的运营。更重要的是，自动驾驶发生故障后，飞行员只能手动操纵飞机飞行，这无疑大大增加了飞行员的工作压力。飞行员对其航司基地所在的北京机场更为熟悉，让飞行员在熟悉的机场落地，更能保障航班安全。
First of all, the aircraft has enough fuel to fly to Beijing. Secondly, the operation and maintenance base of the airline is in Beijing, and flying to Beijing can be repaired as soon as possible to ensure the subsequent operation of the airline. More importantly, after the failure of autopilot, the pilot can only control the aircraft manually, which undoubtedly greatly increases the working pressure of the pilot. The pilot is more familiar with the Beijing airport where his airline base is located, so that the pilot can land at the familiar airport to better ensure flight safety.
这就解释了一些看似「奇怪」的情况：明明马上要到目的地了，目的地天气也很好，出现故障的飞机却要飞往更远的机场备降。
This explains some seemingly strange situations: it is clear that the destination is about to arrive, and the weather at the destination is also good, but the plane with fault has to fly to a further airport for alternate landing.
所以以后坐飞机时，如果再遇到这样的特殊情况，就不用惊慌了。机组总会把各种突发问题安排地明明白白。
So in the future, if you encounter such special circumstances again, you don't have to panic. The crew will always make all kinds of unexpected problems clear.
来自：航旅纵横