Tang Guozheng arrived at the scene a little later, but the rain was heavier.

In order to ensure the integrity of the site as much as possible, the station urgently erected a huge canopy that could cover the Y-8. This left a very important piece of evidence at the scene.

Li Zhan found that the wing had obvious icing, and the flaps were malfunctioning because of the icing. This is completely consistent with his previous judgment. After carefully inspecting the exterior of the fuselage, Li Zhan was surprised to find that the crew and millions of cargo were almost stepping into the ghost gate.

Based on what he knew about the Y-8, this icing in the wings meant that the plane could crash at any moment, perhaps the next second. The successful forced landing of the 8Y1771 cargo flight is simply the favor of the god of fate.

"See what?" Tang Guozheng strode over and asked Li Zhan, who was standing on the wing.

Li Zhan pointed to the wings under his feet and said, "There is obvious icing, and they have walked away from the ghost gate." ”

"Freezing?" Tang Guozheng subconsciously looked out, after the snow stopped, the temperature rose, and the temperature must be above zero at this time, but the temperature in the middle and high altitude was not like that, but the icing phenomenon was not easy to explain.

Li Zhan jumped down directly, clapped his hands and said, "I asked the crew, the de-icing system is on." However, the de-icing system of Yun-8 relies on the heat of the engine to work, and the two engines no longer provide thrust to affect the working effect of the de-icing system, which is basically certain to cause the flaps to be frozen. ”

Zhang Wei added, "Wing icing can affect air flow, and the consequences are no better than flaps being frozen. ”

Pilots are naturally well aware of the consequences of wing icing, and veteran pilots know even more about the power. The wing is the main component that provides lift, and the smooth flow of air from the top and bottom of the wing creates lift or downward pressure that drives the aircraft up or down. Once the smooth flow of air is changed, the wings cannot provide enough lift or downward pressure normally, and the aircraft will go up or down uncontrollably, and the end result is a stall crash.

The consequences of the flaps being frozen are obvious – the pilot has no control over the normal ascent or landing of the aircraft. The crew of the 8Y1771 cargo flight should be glad that they were in the maximum lift position before the flaps were frozen, that is, the take-off and landing positions, otherwise they would not have been able to support the nearby Zhongnan Station.

Tang Guozheng asked Li Zhan curiously, "Do you know Yunba very well?" ”

"I know more than I know any other aircraft." Li Zhan smiled and pointed to the Y-8F-400 lying on the ground tiredly, and said, "I am very familiar with every model of the Y-8, and it is not an exaggeration to say that some models I can even disassemble and assemble with my eyes closed." ”

Tang Guozhenghu asked, "How can you be so familiar with Yunba?" ”

Li Zhan shook his head slightly and said, "I can't say it." ”

Slightly surprised, Tang Guozheng stopped talking about this topic, and Zhang Wei felt even more strange. Li Zhan had never come into contact with the Y-8 during his nine months in the Second Division, and it should be said that except for the J-7E and the J-7, the rest of the models had no contact. Could it be that Li Zhan came into contact with these planes while working in Beiku?

Tang Guozheng looked at the plane, his eyes fell on the blackened engine, frowned and said, "What do you think is the reason why the engine is on fire?" ”

They studied and discussed the civilian Y-8 numbered B-25277 as an aircraft of the troops, and regarded the current accident as an accident of the troops, so they discussed it very seriously. Li Zhan even took this accident as a rare opportunity to engage in actual combat and give full play to his strengths to do some quite useful research and analysis.

Li Zhan said, "It should be caused by a hot start." The fuel supply system did not stop after the two engines stopped working, and the fuel supply was cut off when the unit restarted the engine according to the program, but at this time there was already a lot of fuel in the engine, so it caused a fire after starting the engine with the help of the APU. ”

After a pause, he said, "Engine fire is not the most dangerous situation, I think icing is the main reason why the plane has to make a forced landing." The crew had cut off the fuel supply to the engine that caught fire in time, and it was raining heavily, and the fire in the engine compartment would not develop very much in any case, but would gradually weaken. But the crew did not realize that the loss of function of the two engines affected the normal operation of the de-icing system, and the wings and flaps began to freeze. They thought that the loss of the flaps was due to the fact that the fire in the engine compartment had spread to the wing, but it was not, and the fire was not very big at that time. ”

"Have you removed the cabin sound recorder and the flying ginseng recorder?" Tang Guozheng asked along the way.

Li Zhan said, "You don't need to dismantle it, just extract it directly." ”

Zhang Wei reminded, "Chief of Staff, Captain Li, this is not our plane. ”

The two of them were stunned for a moment, their emotions stopped abruptly, and Li Zhan smiled awkwardly, "Oh yes, it's not our plane, the investigation should be in charge of the Civil Aviation Administration." Yes, I can help them get the investigation done as soon as possible and remove the plane as soon as possible. ”

"It should be fine, they might want us to help." "We can also learn from this. ”

Li Zhan said, "Taking advantage of the fact that the weather has not changed significantly, the chief of staff, send a few people to me, and I will immediately start a preliminary investigation, and some evidence will be fixed." ”

"I will send you someone, but you must get the consent of the Civil Aviation Administration to start an investigation. In this case, on the premise of not affecting the situation on the scene, you can continue the investigation first, and I will immediately ask my superiors for instructions. Tang Guozheng said decisively.

"Yes!"

Zhang Wei asked the people at the station to find a single machine, and according to Li Zhan's instructions, he photographed some parts of the plane, especially several icy areas that had not yet melted. There was no news from Tang Guozheng's side, but Li Zhan's side got more and more information.

Li Zhan's familiarity with the Y-8 series of medium-sized transport aircraft is beyond ordinary people's imagination, and he has really had the experience of disassembling and assembling this type of aircraft with the maintenance team several times. With the help of a few necessary auxiliary equipment, and relying on the tools at hand, they were able to basically disassemble the earlier model of the Y-8 in less than an hour.

The army leaders played the dismantling and combination of light weapons, and Li Zhan and others played the dismantling and combining of aircraft. At the beginning, in order to let the pilots have the ultimate understanding of the aircraft they have mastered, Liu Guojian required every pilot to complete three tests and one assembly test to basically disassemble the aircraft within an hour.

Therefore, Li Zhan is very familiar with every part of the Y-8, just like he is familiar with his own body parts.

A large number of subsequent modifications are inseparable, and Li Zhan and others have been in contact with the follow-up models when they were modified and shipped to the -8, and they are very clear about the situation inside.

Li Zhan is well aware that one of the major shortcomings of the Y-8 series aircraft is that the de-icing and anti-freezing system is not easy to use, and it has not been completely solved so far. In order to prevent accidents due to freezing, a large number of Y-8s were required to be restricted to areas south of the Huai River, and basically not used in plateau areas.

By calculating the meteorological conditions of the airspace where 8Y1771 was located that day, as well as flight parameters, load, unpowered gliding distance and other data, Li Zhan found that the flight could glide to the tourist airport even if there were only two engines left, provided that the de-icing system was turned off.

The engine power occupied by the de-icing system has become the biggest obstacle to limit the arrival of 8Y1771 at the tourist airport, of course, if the de-icing system is not turned on, 8Y1771 may not even be able to reach the Zhongnan Station.

However, this finding is of great significance, which can provide useful reference opinions for manufacturers to improve the de-icing system of the machine. The weather encountered by 8Y1771 is very representative, and in the follow-up large-scale survey, it was found that the same weather often occurs in the central and southern regions, but there has never been a Y-8.

More and more questions have been answered, but what caused the engine to stop has become the last clue. The investigation team of the Civil Aviation Administration of China, with the assistance of the investigation team headed by Li Zhan, made a lot of analysis in the direction, and several possibilities were ruled out.

Seeing that New Year's Day in 2012 was getting closer and closer, Li Zhan raised a possibility - could the problem also be the de-icing system?

This is a known system with congenital defects, and there are no problems under normal circumstances, but in the weather encountered by 8Y1771, the defects in the de-icing system are definitely exposed.

But is there a possible relationship between the de-icing system and the stalling of engines 1 and 2?

Li Zhan told the civil aviation investigation team that the power system used by the Y-8F-400 with the turboprop-6 aero engine as the main component has a device to prevent excessive power, and if the crew does not lift the restriction, then the restriction device will intervene to force the engine power to drop after the engine power exceeds the rated value, and if this phenomenon continues, in order to prevent the engine from overloading and malfunctioning, the restriction device will always intervene, and in this case of continuous intervention, the restriction device may cause the engine to stall.

The de-icing system will continue to ask for energy from the engine when the icing phenomenon still exists, occupying more and more power of the engine, which is completely likely to lead to overload of the engine.

The de-icing system and the engine protection limiter are not smart enough, they are straightforward, and unless the pilot intervenes to adjust the relationship between them, they will always be in a tug-of-war state - the de-icing system is constantly asking for more power, and the engine protection limiter is dragging the engine to avoid overload.

In order to verify Li Zhan's analysis, it was necessary to conduct actual aircraft experiments, and the investigation team requested the assistance of the troops, and the test flight institute in the aircraft city accepted the task. After several days of experiments, the results were transmitted to the Zhongnan Station, and the investigation team was shocked after reading the conclusions—it was completely consistent with Li Zhan's analysis.

No one could have imagined that the interaction between the engine limiter and the de-icing system, which was originally the aircraft's protection device, would become the culprit that almost killed the aircraft.

The conclusion of the investigation of this accident has aroused great attention from the air division and the manufacturer, and a higher-standard investigation team went down to the Zhongnan station before New Year's Day to learn more about the situation. The detailed report of the military-civilian joint investigation team has given the high-level investigation team a treasure and basically determined the direction and methods for solving some problems encountered in the development of the Y-X tactical transport aircraft.

For Li Zhan, the remaining problem was how to get the B-25277 away, and without getting the plane away, his next exploratory flight would not be able to proceed.

The military-civilian joint investigation team came to the scene to discuss the plan.

The first option is to dismantle and transport away. The second option is to use a heavy helicopter to lift it away.

The cargo has already been emptied, and both methods are feasible, but the first solution will cause irreparable damage to the aircraft, because the road down the mountain is difficult to pass the oversized flatbed, and the fuselage must be divided, so that the aircraft can not continue to be used, and the usable parts can only be removed as aviation materials, and the fuselage is put into the furnace.

Option 2 would require the use of the world's largest helicopter, the Mi-26, which would be the only helicopter capable of lifting the Y-8G-400 airframe. However, the wings still needed to be removed to reduce weight and bring them within the allowable payload range of the Mi-26. And it's very dangerous.

On the one hand, the troops continued to empty the runway and resume normal work, and on the other hand, the mail aviation also hoped that the plane could be repaired and put back into operation in the maintenance plant as soon as possible. The loss of a plane grounded for one day is in the hundreds of thousands, and no matter how big the business is, the postal airline will not ignore such a huge loss.

Li Zhan walked to the front of the nose and squatted down, staring at the entire plane lying on the runway in a daze.

Tang Guozheng and Zhang Wei continued to discuss with people from civil aviation, airlines, and insurance companies, and their opinions gradually tended to remove the left and right wings, vertical tail, horizontal wings, landing gear and other large parts with large weights, and then use the Mi-26 to lift them away.

After Zhang Wei found out about Li Zhan's abnormality, he walked over, and also squatted down and looked at the plane with Li Zhan's gaze, "What do you think, the opinions are almost unified, use the second plan." ”

Li Zhan didn't seem to hear Zhang Wei's words, and said to himself, "There is no structural damage to the plane, the friction damage to the belly should not have a great impact, the engine fire has not burned the wings, and the landing gear may not be seriously damaged. ”

"Drive away?" It took a while for Zhang Wei to come back to his senses, and his eyes were about to pop out, "Go away?" You mean just fly away? ”

Li Zhan was still meditating, as if he was calculating something.

Zhang Wei didn't dare to disturb Li Zhan, holding his breath and waiting for Li Zhan's answer.

Suddenly, Li Zhan stood up and raised his hand and said loudly, "Plan three!" Left! The plane can fly away directly! ”

The members of the military-ground investigation team who formed a circle at the nose of the plane on the right side of the plane looked over in unison.

Someone said, "Fly away? Dreaming in broad daylight. ”

More people fell into deep thought after being surprised, and once again re-examined the B25277 lying on the ground - the plane seemed to have no major damage other than two engine damage.

More and more people fell into deep thought, then thoughtfulness, and by the time several technicians walked briskly around the plane to observe, almost all of them were in sight.

They realized that this might be the best way to go.

PS: I have to look at the day of the plane crash before going to bed these days......