Cause of Fatal Plane Crash: Bald Eagle Four people were killed in the April crash in Alaska By Newser Editors and Wire Services Posted May 4, 2016 6:58 PM CDT 36 comments Comments (Shutterstock) (Newser) – A small airplane hit a bald eagle before it crashed and burst into flames in Alaska last month, killing all four people on board, the AP reports. It's the nation's first civilian plane crash to result in deaths after an impact with a bald eagle, said Shaun Williams, a National Transportation Safety Board investigator. The pilot, co-pilot and two passengers died when the plane went down April 20 near a small airport about 20 miles north of downtown Anchorage. They were conducting an aerial survey for a private firm. Investigators found an unidentified substance on several portions of the plane's frame and sent samples to the Smithsonian Institute in Washington, DC, for forensic analysis. "There, they were able to determine that the portions of feather and other material came from an immature bald eagle," Williams said. There were other eagles "observed over the crash site and in the immediate vicinity," he added. The Alaska Department of Fish and Game says Alaska has the largest population of bald eagles, which are found only in North America. It puts the Alaska bald eagle population at about 30,000 birds.