Doug Butzier, the Libertarian Party nominee for U.S. Senate in Iowa, was killed in a plane crash, authorities said Tuesday. He was 59.

Key West Fire Chief Brian Arnold confirmed the crash and Butzier's death in a brief interview. He said Butzier was piloting an airplane late Monday night when it crashed roughly a mile from the Dubuque airport, which Butzier was approaching. No one else was in the plane.

The National Transportation Safety Board said it is investigating a crash in the Dubuque area that caused no ground injuries.

The flight originated from Ankeny Regional Airport, a Federal Aviation Administration spokesman said.

"A single-engine Piper PA-46 crashed at about 11 p.m. Central Time on Monday while on approach to Dubuque Regional Airport in Dubuque, Iowa," said FAA spokesman Lynn Lunsford in a statement. "The aircraft went down about a mile north of the runway."

Butzier, an emergency room doctor, was a long-shot against state Sen. Joni Ernst (R) and Rep. Bruce Braley (D). Ernst offered condolences on Twitter:

In a statement, Braley said he was “shocked and saddened to hear of the sudden and tragic death of Doug Butzier. I have enormous respect for anyone who puts their name forward as a candidate for public office. Carolyn and I send our thoughts and prayers to Dr. Butzier’s wife and family during this difficult time.”​