What may be the reasons for any air crash?

There are many explanations for an airplane crash. Usually the crash is a result of more than 2 reasons. Just like a car accident, it usually occurs when one driver is distracted and the other driver is speeding and the roads are slippery with rain.

The general categories for airplane crashes include:

Weather - 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. An example of this John Kennedy's plane that was lost at night in the ocean near Marthar's Vineyard.

Mechanical - 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.

Pilot Error - this can vary from not paying attention to his instruments or watching for other a/c. People are only human so many accidents are attributed to poor judegment of the pilot. For example; the weather may be getting bad but the pilot chooses to fly into the storm. Larger passenger airliners have 2 or more flight crew which helps eliminate some human errors.

Air Traffic Controller - Sometimes the traffic controller gives the "Clear to Takeoff" or similar instructions that result in an accident.

A new one is called:

Cockpit Management - Airlines now stress that the Pilot In Command should keep control of the situation and accept inputs from his crew without judging them. If the Pilot In Command begins to ignore or judge the recommendations of the crew, the crew will not function as a team and someone will over-look something that will lead to an accident.

Fuel Starvation - This is really a subset of Pilot Error but it can be the result of several factors.