We asked a pilot to explain how high planes fly and why they need to maintain cruising altitude. Here's what he had to say.

The military helicopter that collided with an American Airlines flight over Washington, DC, was flying nearly twice as high as it should ... as the plane was landing, killing 67 people aboard ...

which served as a chase plane. The planes were soaring high in Chengdu, Sichuan, China on Dec. 26, which is notably the birthday of the founding father of the People's Republic of China ...

“It seems clear from the preliminary report that the first officer negligently piloted and slammed the plane into the ground at a high sink rate of over 1000 feet per minute and at a bank angle ...