The fine volcanic ash contains silicon dioxide, and the melting point of this compound is 1100 degrees Celsius. At present, the operating temperature of the turbine engine of most aircraft is 1400 degrees Celsius. Once the volcanic ash is sucked into the interior of the engine, the silica will be adsorbed on the turbine after melting. The blades and turbines guided the blades, leading to catastrophic consequences. In 1982, two aircraft passed through the volcanic ash erupting from the Kalungong volcano in West Java, Indonesia. All eight engines of the two aircraft were stopped, ranging from 11,000 meters. After a high altitude glide to 400 meters, it restarted to make an emergency landing. What does this text mainly introduce? ['Volcanic ash has a serious impact on aircraft flight.', 'Silica is the main component of volcanic ash.', 'Cooling allows the aircraft to effectively avoid the dangers of volcanic ash.', 'The volcanic eruption has historically caused flight accidents.']