The crash of an Asiana Airlines Boeing 777 at San Francisco Airport, killing three Chinese girls, has raised public concerns about aviation safety  Statistics show that from the 1950s to the present, the accident rate of civil flights has been declining  The number of deaths per 100 million passenger kilometers was 2 78 in 1945, 0 90 in the 1950s, and 0 013 in the past 30 years
However, the absolute number of civil aviation accidents has increased in recent decades
In recent decades, the earth's climate has changed abnormally, and severe weather such as fog has increased.