Topeka ? An officer finishing his training for the Topeka Police helicopter unit was injured when the craft he was piloting went down in rural Riley County, authorities said.

Conrad Unruh, 37, a six-year veteran of the force, was listed in stable condition at a Topeka hospital after the Friday afternoon crash, said police spokeswoman Kristi Pankratz.

Pankratz said Unruh, a certified pilot for fixed-wing aircraft, had been training to join the helicopter unit for several months. The solo flight he was making would have concluded his testing for certification in rotor-wing aircraft.

The helicopter went down in a Flint Hills pasture within seven miles of his Manhattan destination.

The Kansas Highway Patrol said the “aircraft lost RPMs in the rotors, which led to engine malfunction.”

The two remaining department helicopters will be grounded until the investigation of the crash is completed, Maj. John Sidwell said.

The police helicopter unit was established in 1971. One officer died in a crash three years later, and two other officers were killed in a 2000 crash.

A fourth helicopter crash in Topeka, involving a LifeStar helicopter ambulance, occurred in 1998 at Forbes Field. That crash happened during a routine training flight for LifeStar. The three people aboard that helicopter escaped with minor injuries.

The fatal crashes raised questions about the future of the unit, but authorities decided it was worthwhile.

The police helicopter unit again became a subject of public scrutiny in 2004 after a consultant suggested an alternative program with potential savings of up to $761,000 annually.