- Like strike a bird...
Ex.: A US Airways plane has crashed into the Hudson River in New York City, after being struck by birds that disabled two engines.
- Poor visibility. Icing conditions. Some pilots are not trained or equipped to fly at night and find themselves having to continue flying to reach an airport after it gets dark.
Ex.: Cargo plane crashes at Japan´s Narita airport
- This can be a failure of a part during normal service. Most aircraft systems have built-in redundancy so that a failure of one part will not create an unsafe condition. Some mechanical failures is due to bad maintenance; such as someone forgetting to tighten a bolt.
Ex.: 16 missing in helicopter crash off Newfoundland
- This is really a subset of Pilot Error but it can be the result of several factors.