CHEYENNE, Wyo. (AP) - A voice recording shows a single-engine airplane was struggling to get over Wyoming's highest mountain range in bad weather before it crashed and killed the pilot and three of his young sons. The Oct. 25 crash in the Wind River Range killed 40-year-old Luke Bucklin of Minneapolis, his 14-year-old twins, Nate and Nick, and 12-year-old son Noah. On the recording, Bucklin says his plane is climbing slowly and may not reach 16,000 feet, the altitude he was assigned by an air traffic controller. About 2 1/2 minutes later, Bucklin says the plane is caught in up-and-down wind currents called mountain waves. The plane crashed shortly after that. The AP obtained the Federal Aviation Administration recording through the Freedom of Information Act.