Meeting the ground: how planes land

A modern passenger jet airliner is designed for flights at altitudes of about 9-12 thousand meters. It is there, in very thin air, that it can move in the most economical mode and demonstrate its optimal speed and aerodynamic characteristics. The interval from the completion of climb to the start of the descent is called flying on a cruising level. The first step in preparing for landing will be a descent from the train, or, in other words, following the route of arrival. The end point of this route is the so-called control point of the initial approach phase. In English, it is called Initial Approach Fix (IAF).

A 380 lands on a strip of water. Tests have shown that the aircraft is able to land in crosswinds with gusts of up to 74 km / h (20 m / s). Although reverse braking devices are optional according to FAA and EASA requirements, Airbus designers decided to equip them with two engines closer to the fuselage. This made it possible to obtain an additional braking system, while reducing operating costs and reducing the preparation time for the next flight.

From the IAF point, the movement begins according to the scheme of approach to the aerodrome and approach, which is developed separately for each airport. The approach according to the scheme involves a further decrease, the passage of the trajectory specified by a number of control points with certain coordinates, often making turns and, finally, reaching the landing line. At a certain point, the landing straight liner enters the glide path. Glissade (from the French glissade - gliding) is an imaginary line connecting the entry point to the start of the runway. Passing along the glide path, the aircraft reaches the point MAPt (Missed Approach Point), or the point of departure to the second circle. This point is passed at the decision-making altitude (VLR), that is, the height at which the maneuver for approaching the second circle should be started if, before reaching it, the aircraft commander (FAC) did not establish the necessary visual contact with the reference points to continue the approach. Before VPR, the PIC should already assess the position of the aircraft relative to the runway and give the command "Sit down" or "Leave."

Chassis, Flaps and Economy

On September 21, 2001, an IL-86 aircraft owned by one of the Russian airlines landed at Dubai Airport (UAE) without landing gear. The case ended in a fire in two engines and the cancellation of the liner - fortunately, no one was hurt. There was no question of a technical malfunction, just the chassis ... forgot to release.

With everything as before Modern airliners are literally packed with electronics in comparison with aircraft of past generations. They implement a fly-by-wire remote control system (literally "fly by wire). This means that the rudders and mechanization are driven by actuators that receive commands in the form of digital signals. Even if the plane does not fly in automatic mode, the steering wheel movements are not transmitted directly to the wheels, but are recorded in the form of a digital code and sent to a computer that instantly processes the data and gives a command to the executive device. In order to increase the reliability of automatic systems, two identical computer devices (FMC, Flight Management Computer) are installed in the aircraft, which constantly exchange information, checking each other. Into the FMC, a flight task is introduced indicating the coordinates of the points through which the flight path will run. Along this trajectory, electronics can fly an aircraft without human intervention. But the rudders and mechanization (flaps, slats, spoilers) of modern liners are not much different from the same devices in models released decades ago. 1. Flaps. 2. Interceptors (spoilers). 3. Slats. 4. Ailerons. 5. The rudder. 6. Stabilizers. 7. Rudder.

The economy is related to the background of this accident. Approach to the airfield and approach associated with a gradual decrease in aircraft speed. Since the magnitude of the wing lift is directly dependent on both the speed and the wing area, in order to maintain a lift that is sufficient to keep the machine from stalling, it is necessary to increase the wing area. For this purpose, mechanization elements are used - flaps and slats. Flaps and slats perform the same role as the feathers that the birds fan out before dropping to the ground. When the speed of the start of mechanization production is reached, the PIC gives a command to release the flaps and almost simultaneously - to increase the engine operating mode to prevent critical speed loss due to an increase in drag. The more flaps / slats are deflected at a larger angle, the larger the engines need. Therefore, the closer to the strip the final release of the mechanization takes place (flaps / slats and chassis), the less fuel will be burned.

Patriarch of Small Aviation: An-2 "Corn"

On domestic aircraft of the old types, such a sequence of mechanization was adopted. At first (20–25 km to the strip) a chassis was produced. Then, for 18–20 km, there were 280 flaps. And already on the landing straight flaps they were fully extended to the landing position. However, a different methodology has been adopted these days. In order to save money, pilots try to fly the maximum distance “on a clean wing”, and then, in front of the glide path, extinguish the speed by intermediate flap release, then release the landing gear, bring the flap angle to the landing position and land.

Approach scheme The figure shows a very simplified approach and take-off scheme in the airport area. In fact, the schemes can differ markedly from airport to airport, as they are made taking into account the terrain, the presence of high-rise buildings and forbidden zones near the flight. Sometimes for the same airport there are several schemes depending on weather conditions. So, for example, in Moscow Vnukovo, when entering the strip (GDP 24), the so-called a short diagram, the trajectory of which lies outside the Moscow Ring Road. But in bad weather, airplanes come in according to a long pattern, and liners fly over the South-West of Moscow.

The crew of the ill-fated IL-86 also took advantage of the new technique and released flaps to the chassis. The Il-86 automation, which did not know anything about new trends in piloting, immediately turned on the voice and light signaling, which required the crew to release the chassis. So that the alarm did not irritate the pilots, it was simply turned off, as the annoying alarm clock turned off. Now, there was no one to remind the crew that the chassis still needed to be released. Today, however, copies of Tu-154 and Il-86 aircraft with modified alarms have already appeared, which fly by the approach method with the late release of mechanization.

According to actual weather

In informational reports one can often hear a similar phrase: “In connection with the deteriorating weather conditions in the area of ​​airport N, crews make decisions about take-off and landing in actual weather.” This common stamp causes both domestic aviators laughter and indignation. Of course, there is no arbitrariness in the flight business. When the aircraft passes the decision point, the aircraft commander (and only he) finally announces whether the crew will land the liner or the landing will be interrupted by leaving on the second circle. Even under the best weather conditions and the absence of obstacles in the airfield, the PIC has the right to cancel a landing if he, as the Federal Aviation Rules say, “is not sure of a successful landing outcome”. “Going to the second round today is not considered a miscalculation in the work of the pilot, but rather, is welcomed in all situations of doubt. It’s better to be vigilant and even sacrifice some burned fuel than to endanger even the slightest risk to the lives of passengers and crew, ”Igor Bocharov, chief of flight operations staff at S7 Airlines, explained to us.

Course-glide path system Course-glide path system consists of two parts: a pair of course and a pair of glide path beacons. Two directional beacons are located behind the runway and emit a directed radio signal along it at different frequencies at small angles. On the runway center line, the intensity of both signals is the same. To the left and to the right of this direct signal of one of the lighthouses is stronger than the other. By comparing the signal strength, the aircraft’s radio navigation system determines which side and how far it is from the center line. Two glide slope beacons located in the area of ​​the landing zone act in a similar way, only in the vertical plane.

On the other hand, in the decision-making process, the PIC is strictly limited by the existing regulations of the landing procedure, and within this regulation (except for emergency situations like a fire on board) the crew has no freedom of decision-making. There is a strict classification of approach types. For each of them, separate parameters are prescribed that determine the possibility or impossibility of such a landing in these conditions.

For example, for Vnukovo Airport, an inaccurate instrumental approach approach (for driving radio stations) requires passing the decision point at an altitude of 115 m with a horizontal visibility of 1700 m (determined by the weather service). To make a landing before VPR (in this case 115 m), visual contact with landmarks should be established. For automatic landing according to ICAO Category II, these values ​​are much smaller - they are 30 m and 350 m. Category IIIc allows a fully automatic landing with zero horizontal and vertical visibility - for example, in complete fog.

Safe stiffness

Any air passenger with experience in flying domestic and foreign airlines probably managed to notice that our pilots land aircraft “softly” and foreign ones “hard”. In other words, in the second case, the moment of touching the strip is felt in the form of a noticeable push, while in the first case, the plane gently “rubbed” against the strip. The difference in landing style is explained not only by the traditions of flight schools, but also by objective factors.

To begin with, we introduce terminological clarity. A hard landing in aviation is called landing with an overload that greatly exceeds the standard. As a result of such a landing, the aircraft in the worst case receives damage in the form of permanent deformation, and at best it requires special technical maintenance aimed at additional monitoring of the state of the aircraft. As Igor Kulik, lead pilot instructor of the S7 Airlines flight standards department, explained to us, today a pilot who made a real hard landing is suspended from flights and sent to additional training on simulators. Before entering the flight again, the offender will also have a test-training flight with an instructor.

The landing style on modern Western aircraft cannot be called hard - it is simply a matter of increased overload (of the order of 1.4–1.5 g) compared to 1.2–1.3 g characteristic of the “domestic” tradition. If we talk about the piloting technique, the difference between landings with relatively less and relatively greater overload is explained by the difference in the leveling procedure of the aircraft.

To alignment, that is, to prepare for touching the ground, the pilot proceeds immediately after the passage of the end of the strip. At this time, the pilot takes over the helm, increasing the pitch and putting the aircraft in a cabriolet position. Simply put, the plane "lifts its nose", thereby achieving an increase in the angle of attack, which means a small increase in lift and a drop in vertical speed.

At the same time, the engines are switched to the "low gas" mode. After a while, the rear landing gears touch the strip. Then, reducing the pitch, the pilot lowers the front pillar onto the strip. At the moment of contact, interceptors are activated (spoilers, they are also air brakes). Then, reducing the pitch, the pilot lowers the front strut onto the strip and turns on the reversing device, that is, it additionally slows down the engines. Wheel braking is used, as a rule, in the second half of the run. The reverse constructively consists of shields that are placed in the path of a jet stream, deflecting part of the gases at an angle of 45 degrees to the course of the aircraft — almost in the opposite direction. It should be noted that on aircraft of old domestic types, the use of reverse during mileage is mandatory.


Silence overboard

On August 24, 2001, the crew of the Airbus A330, flying from Toronto to Lisbon, discovered a fuel leak in one of the tanks. It was happening in the sky over the Atlantic. The commander of the ship, Robert Peach, decided to leave for the alternate aerodrome located on one of the Azores. However, on the way both engines caught fire and failed, and about 200 kilometers remained to the airfield. Rejecting the idea of ​​landing on water, as giving almost no chance of salvation, Peach decided to reach the land in the planning mode. And he succeeded! The landing turned out to be tough - almost all pneumatics burst - but the disaster did not happen. Only 11 people received minor injuries.

Domestic pilots, especially those operating Soviet-style airliners (Tu-154, Il-86), often complete the alignment with the aging procedure, that is, they continue to fly over the strip at a height of about a meter for some time, achieving a soft touch. Of course, passengers are more comfortable with holding landings, and many pilots, especially those with extensive experience in domestic aviation, consider this style to be a sign of high skill.

However, today's global trends in aircraft design and piloting prefer landing with an overload of 1.4-1.5 g. Firstly, such landings are safer, as long-standing landings pose a risk of rolling out of the lane. In this case, the use of reverse is almost inevitable, which creates additional noise and increases fuel consumption. Secondly, the design of modern passenger airplanes provides for touch with increased overload, since the operation of automation, for example, the use of spoilers and wheel brakes, depends on a certain value of the physical impact on the landing gear (compression). In older types of aircraft this is not required, since spoilers turn on there automatically after turning on the reverse. And the reverse is included by the crew.

There is another reason for the difference in landing style, say, for those close to the Tu-154 and A 320 class. The runways in the USSR were often notable for low cargo intensity, and therefore the Soviet aviation tried to avoid too much pressure on the coating. On the trolleys of the rear struts of the Tu-154 with six wheels - this design contributed to the distribution of the weight of the machine over a large area during landing. But the A 320 has only two wheels on racks, and it was originally designed for landing with a greater overload on more durable bands.

The abundant Saint-Martin The island of Saint-Martin in the Caribbean, divided between France and the Netherlands, gained notoriety not only because of its hotels and beaches, but because of the landing of civilian liners. Heavy wide-bodied Boeing 747 or A-340 aircraft fly to this tropical paradise from all over the world. Such cars need a long run after landing, but at Princess Juliana's airport the strip is too short - only 2130 meters - its end face is separated from the sea only by a narrow strip of land with a beach. To avoid rolling out, airbus pilots aim at the very end of the strip, flying 10-20 meters above the heads of vacationers on the beach. This is how the glide path trajectory is laid. Photos and videos with landings on about. Saint-Martin has long gone around the Internet, and many at first did not believe in the authenticity of these shootings.

Troubles near the earth

And yet, really hard landing, as well as other troubles in the final segment of the flight happen. As a rule, it is not one, but several factors that lead to air accidents, including piloting errors, equipment failure, and, of course, the elements.

Of great danger is the so-called wind shear, that is, a sharp change in wind strength with height, especially when it occurs within 100 m above the ground. Suppose a plane approaches a strip with an instrument speed of 250 km / h in zero wind. But, having descended a little lower, the plane suddenly encounters a fair wind at a speed of 50 km / h. The air pressure will drop, and the speed of the aircraft will be 200 km / h. The lift will also decrease sharply, but the vertical speed will increase. To compensate for the loss of lift, the crew will need to add engine mode and increase speed. However, the aircraft has a huge inertial mass, and it simply won’t be able to instantly gain sufficient speed. Если нет запаса по высоте, жесткой посадки избежать не удастся. Если же лайнер натолкнется на резкий порыв встречного ветра, подъемная сила, наоборот, увеличится, и тогда появится опасность позднего приземления и выкатывания за пределы полосы. К выкатываниям также приводит посадка на мокрую и обледеневшую полосу.


Человек и автомат

Типы захода на посадку делятся на две категории, визуальные и инструментальные.

Условие для визуального захода на посадку, как и при инструментальном заходе, — высота нижней границы облаков и дальность видимости на ВПП. Экипаж следует по схеме захода, ориентируясь по ландшафту и наземным объектам или самостоятельно выбирая траекторию захода в пределах выделенной зоны визуального маневрирования (она задается как половина окружности с центром в торце полосы). Визуальные посадки позволяют сэкономить топливо, выбрав кратчайшую на данный момент траекторию захода.

Вторая категория посадок — инструментальные (Instrumental Landing System, ILS). Они в свою очередь подразделяются на точные и неточные. Точные посадки производятся по курсо-глиссадной, или радиомаячной, системе, с помощью курсовых и глиссадных маяков. Маяки формируют два плоских радиолуча — один горизонтальный, изображающий глиссаду, другой — вертикальный, обозначающий курс на полосу. В зависимости от оборудования самолета курсо-глиссадная система позволяет производить автоматическую посадку (автопилот сам ведет самолет по глиссаде, получая сигнал радиомаяков), директорную посадку (на командном приборе две директорные планки показывают положения глиссады и курса; задача пилота, работая штурвалом, поместить их точно по центру командного прибора) или заход по маякам (перекрещенные стрелки на командном приборе изображают курс и глиссаду, а кружком показано положение самолета относительно требуемого курса; задача — совместить кружок с центром перекрестья). Неточные посадки выполняются при отсутствии курсо-глиссадной системы. Линия приближения к торцу полосы задается радиотехническим средством — например, установленными на определенном удалении от торца дальней и ближней приводными радиостанциями с маркерами (ДПРМ — 4 км, БПРМ — 1 км). Получая сигналы от «приводов», магнитный компас в кабине пилотов показывает, справа или слева от полосы находится самолет. В аэропортах, оснащенных курсо-глиссадной системой, значительная часть посадок совершается по приборам в автоматическом режиме. Международная организация ИКФО утвердила список из трех категорий автоматической посадки, причем категория III имеет три подкатегории — A, B, C. Для каждого типа и категории посадки существуют два определяющих параметра — расстояние горизонтальной видимости и высота вертикальной видимости, она же высота принятия решений. В общем виде принцип таков: чем больше в посадке участвует автоматика и чем меньше задействован «человеческий фактор», тем меньше значения этих параметров.

Другой бич авиации — боковой ветер. Когда при подходе к торцу полосы самолет летит с углом сноса, у пилота часто появляется желание «подвернуть» штурвалом, поставить самолет на точный курс. При довороте возникает крен, и самолет подставляет ветру большую площадь. Лайнер сдувает еще дальше в сторону, и в этом случае единственно правильным решением становится уход на второй круг.

При боковом ветре экипаж часто стремится не потерять контроль за направлением, но в итоге теряет контроль за высотой. Это стало одной из причин катастрофы Ту-134 в Самаре 17 марта 2007 года. Сочетание «человеческого фактора» с плохой погодой стоило жизни шести людям.

Иногда к жесткой посадке с катастрофическими последствиями приводит неправильное вертикальное маневрирование на заключительном отрезке полета. Порой самолет не успевает снизиться на требуемую высоту и оказывается выше глиссады. Пилот начинает «отдавать штурвал», пытаясь выйти на траекторию глиссады. При этом резко возрастает вертикальная скорость. Однако при возросшей вертикальной скорости требуется и большая высота, на которой надо начинать выравнивание перед касанием, причем эта зависимость квадратичная. Летчик же приступает к выравниванию на психологически привычной ему высоте. В результате воздушное судно касается земли с огромной перегрузкой и разбивается. Таких случаев история гражданской авиации знает немало.

Авиалайнеры последних поколений можно вполне назвать летающими роботами. Сегодня через 20−30 секунд после взлета экипаж в принципе может включить автопилот и дальше машина все сделает сама. Если не случится чрезвычайных обстоятельств, если в базу данных бортовых компьютеров будет введен точный план полета, включающий траекторию захода на посадку, если аэропорт прибытия обладает соответствующим современным оборудованием, лайнер сможет выполнить полет и совершить посадку без участия человека. К сожалению, в реальности даже самая совершенная техника иногда подводит, в эксплуатации все еще находятся воздушные суда устаревших конструкций, а оборудование российских аэропортов продолжает желать лучшего. Именно поэтому, поднимаясь в небо, а затем спускаясь на землю, мы еще во многом зависим от мастерства тех, кто работает в пилотской кабине.

Благодарим за помощь представителей авиакомпании «S7 Airlines» — пилота-инструктора Ил-86, начальника штаба летной эксплуатации Игоря Бочарова, главного штурмана Вячеслава Феденко, пилота-инструктора директората департамента летных стандартов Игоря Кулика

Статья «Встреча с землей» опубликована в журнале «Популярная механика» (№9, Сентябрь 2008). I wonder how a nuclear reactor works and can robots build a house?

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