Several crew members were convinced from the start that it was a hostile military plane, and from that point on they filtered all the information coming in. The crew had rehearsed the a training scenario many times on what to do when there is a hostile military plane in their air space. They ignored evidence that it was, in fact, a commercial plane, paid attention only to the information that led them to think it was a hostile military craft, and then proceeded to carry out the training scenario. All leading them to an incorrect resolution.

https://www.blog.theteamw.com/2011/04/02/100-things-you-should-know-about-people-97-people-filter-information/