By Brendan O'Brien

(Reuters) - A Libertarian Party candidate for Iowa's U.S. Senate seat has died in the crash of a small airplane near Dubuque Regional Airport in Iowa, authorities said on Tuesday.

Dr. Douglas Butzier died when the single-engine airplane he was piloting crashed late Monday about a mile north of the airport's runway, the Dubuque Sheriff's Department said in a statement.

Butzier, 59, who was alone in the Piper airplane, had taken off about an hour earlier from Ankeny Regional Airport north of Des Moines, Iowa, authorities said.

Butzier was president of the medical staff and a member of the board of trustees at Mercy Medical Center in Dubuque, where he had served in the emergency department for 17 years, the hospital said.

"He was a leader among his peers, and we will all miss his strong, intelligent, thoughtful presence, and we express our collective condolences to Doug's family, friends, and colleagues," Russell Knight, Mercy president and chief executive officer, said in a statement.

Butzier had no previous political experience and had 2 percent support in a recent Public Policy polling survey for the open U.S. Senate seat. The top candidates are Republican Joni Ernst and Democrat Bruce Braley.

(Reporting by Brendan O'Brien in Milwaukee; Editing by Peter Galloway)