Civil Aviation Resource Network May 19, 2010 News: Summer flight is destined to deal with thunderstorm weather. Lei Yusheng has the unfavorable characteristics of â€œstrong bumpsâ€, â€œlightningâ€, â€œiceâ€ and â€œstrong precipitationâ€ that pose a serious threat to flight safety. Aviation meteorology generally divides thunderstorm into three types: â€œhot thunderstormâ€, â€œterrain thunderstormâ€ and â€œfront thunderstormâ€. "Hot Thunderstorm" is isolated and dispersed, and the range is small and slow. It is formed by the warming of the surface hot air and the expansion of the air vapor. It is best to be strong at 2 o'clock in the summer, much like the mushroom cloud pillar formed after the atomic bomb. Whether it is visual or weather radar, it is good to judge. Most of the "topographic thunderstorms" are born in hills and mountainous areas. They are raised by the moist air currents in the summer. The development is not fast. The precipitation is often mixed with hail, and the airflow is very strong. Near the thunderstorm, you can feel the bumps. How powerful. The "frontal thunderstorm" is formed by the system weather, and it is more than a thousand miles. If it is on the route, it is difficult to get around unless there is a gap.
The main hazards of thunderstorms are as follows: First, strong electron currents form lightning strikes. If the aircraft encounters strong electron current, it will damage the radome, antenna, windshield, wing, horizontal stabilizer and protrusion with small radius of curvature, which will cause the body to ablate. A Boeing 757 in a company was struck by lightning in the Chengdu area, and its control surface was hit by a big mouth that was more than a dozen centimeters long.
The second is a strong bump, resulting in structural deformation of the body.
The third is to collide with the hail in the cloud at high speed, causing damage to the body and engine blades.
Fourth, entering the strong precipitation area, it is easy to induce the engine to stop, and the surface of the wing and the fuselage is rough, the resistance is increased, the angle of attack is reduced, the lift resistance is reduced, the stall speed is increased, and the aerodynamic performance of the aircraft is seriously reduced.
Fifth, entering the thunderstorm area during take-off and landing, it is likely to encounter low-level wind shear. Because there is often wind shear at the bottom of thunderstorms and heavy rains, low altitudes encounter strong downdrafts, which is difficult to dispose of.
Modern flight, especially in the clouds and at night, is it based on meteorological radar to determine the nature of the cloud system in front? Is it dangerous? Is it a direct crossing or a circumvention? Can give the pilot an intuitive guidance. Weather radars determine the weather ahead by detecting the size and number of rainfall droplets. The larger and denser the water droplets, the stronger the reflected echoes on the radar. Judging the intensity of thunderstorms on the radar is represented by four colors: "green", "yellow", "red", and "purple":
Green indicates weak precipitation with a precipitation rate of 0.03-0.15 inches/hour;
Yellow indicates moderate precipitation with a precipitation rate of 0.15-0.5 inches per hour;
Red indicates strong or strong precipitation with a precipitation rate of 0.5-2 inches per hour;
Purple indicates severe or extreme precipitation with a precipitation rate of 2-5 inches per hour.
The meteorological radar detects the front weather only by scanning a part of a certain height within 180 degrees in front of it, similar to a watermelon slice sliced â€‹â€‹by a flap, and its beam thickness = distance Ã— 100 Ã— beam focusing angle .
For example, when the Boeing 757-200 aircraft is set to 80 nautical miles, the beam thickness is 80Ã—100Ã—3.5=28,000 feet from its 80 nautical miles. When the altitude is below 8400 meters, the radar selection distance is still 80 nautical miles, the angle of the antenna is 0 degrees or negative, the radar echo may have errors because the lower half of the probe beam has touched the ground. The echoes displayed on the screen are not just thunderstorms, they are likely to include reflected echoes from the ground buildings.
Therefore, the selection of the pitch angle of the radar antenna in flight is quite learned. Many seniors have great experience in this. According to the flight practice, it is recommended to pay attention to the following points:
1. When taking off, the elevation angle on the antenna is adjusted to +5 degrees. If there is a mountain in front, it should be increased to +7 degrees.
2. During the climb, as the altitude increases, the elevation angle on the antenna gradually decreases. 5000 feet or less / +5 degrees, 5000-10000 feet / +1 degree, 10,000-15,000 feet / 0 degrees, 15000 - 20000 feet / - 0.5 degrees.
3. When flying in a plane flight, the angle of the antenna is approximately -1.5 degrees - 1.75 degrees, so that the ground echo is just after the outermost end of the radar display, and then slightly up, until the ground echo disappears. should.
The antenna angle is also related to the selected radar detection distance.
When the cruising altitude is 15,000 feet or less, the distance from the antenna angle is: 40 nautical miles / +2 degrees, 80 nautical miles / +1.5 degrees, 160 nautical miles / +0.75 degrees.
When the cruising altitude is 25,000 feet or more, the relationship between the distance and the antenna angle is: 40 nautical miles / 0 degrees, 80 nautical miles / -0.5 degrees, 160 nautical miles / 1.25 degrees.
4. In the fall, for every 10,000 feet drop in the initial period, the elevation angle of the antenna should be raised by 1 degree, and the height should be below 15,000 feet. For every 5,000 feet, it is necessary to raise the elevation angle by 1 degree.
5. In the five-sided approach, in order to facilitate the selection of a suitable ascending route for the go-around, the antenna elevation angle should be adjusted to +7-+10 degrees.
In addition, the use of meteorological radar "distance circle" and "gain" button should also pay attention to the method, in order to prevent the latter thunderstorm from being blocked by the front, not caught in time and caught in a difficult situation. If there are two radar screens in the cockpit, the distance circle of each part should be different for comparison; if there is only one display, you must change the distance circle as needed to search. If the screen displays a large red area (especially flying Hong Kong, the sea is humid, it is easy to make red), in order to accurately determine the weather ahead, avoid the strongest part, you can gradually reduce the "gain" knob and pay attention to which part stays red. The longest, then this part is the strongest place, and you should not avoid it. It should be avoided as far as possible according to the flight rules.
Experienced pilots know that there are special shapes such as â€œU-shapedâ€, â€œfinger-typeâ€, â€œscallop-sideâ€, and â€œhook-typeâ€ on the weather radar display, although these areas are located. The green areas outside the strong precipitation area, but most of them contain hailstones. When flying around such clouds, it is best to fly around the wind to avoid being hit by hail and eating hard.
Boeing has a small suggestion for the determination of the height of the front cloud in the cloud or at night. If the radar distance is 80 or 100 nautical miles and the screen is displayed, the dangerous weather may be higher than the cruising altitude. It may be low, and the angle of the Wu line can be adjusted to +1.2 degrees or +1.5 degrees. If the display disappears, the dangerous weather is lower than mine, and the method of flying over can be adopted; if it still exists, it means higher than me and must fly around. Of course, you can also continue to keep the antenna at 0 degrees and fly to 50-60 nautical miles. If the previous display disappears, it means that the dangerous weather is lower than mine. You can still fly directly because the plane is flying vertically to the top of the cloud. At least 7000-9000 feet away, there should be no danger. However, any thunderstorm cloud with more than 35,000 feet at the top is best not to take the form of overflight.
In order to ensure that the weather radar can be used normally in the air, the TEST test must be carried out on the ground. At this point, the flight must be completed during the summer. If you perform a power-on check, the following precautions should be followed:
1. When refueling or pumping is being carried out in or near the aircraft, the weather radar shall not be in a launching state to avoid igniting the gasoline vapor. When using a large number of gasoline cleaning parts on the apron, you should also avoid using the radar power supply. However, it can be placed in the "TEST" position for simulation testing.
2. The weather radar should not be in the launch state in the hangar or in the case of the building facing a close-range building or large metal reflecting surface, so as to avoid damage to the weather radar receiver due to excessive echo.
3. When inspecting meteorological radars on the ground, the weather radar should be operated as far as possible in preparation or self-test mode. When it is necessary to make the radar work in the transmission mode, the antenna pitch knob should be adjusted to 10-15 degrees of upward tilt to avoid the antenna beam from illuminating the near ground target.
It is well known that long-term exposure to a certain dose of microwave radiation is detrimental to human health. The radar antenna has a strong directivity, which concentrates the microwave energy in the longitudinal direction of the antenna, thereby greatly increasing the intensity of the microwave radiation in this direction. Therefore, when the weather radar is energized on the ground, it is necessary to prevent the damage of the microwave energy generated by the radar to the human body. This is not an extra word.
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