The National Transportation Safety Board says the crew mismanaged the plane's descent being carried out without the help of navigational instruments.
Officials also say one of the pilots deactivated a system that automatically regulates airspeed.
Investigators also say the crew delayed its decision to abort the landing with the plane flying too slowly.
Three people were killed in the crash with nearly 200 more injured.
Copyright 2015 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.