The type of helicopter that crashed in a central Minnesota farm field Thursday is the military's long-running workhorse with a reputation of reliability.

While the National Guard helicopter crash is still under investigation, questions surfaced Thursday about the Sikorsky UH-60 Black Hawk involved in the incident.

The possible causes of the crash fall into three camps: a material, maintenance or circumstantial failure. Most incidents involving this type of helicopter fall into the third category, which could include weather or poor visibility that could cause a pilot to inadvertently run into power lines or trees, said Lee Benson, the former chief pilot for the Los Angeles County Fire Department, where he flew UH-60 Black Hawks.

However, the National Guard said this helicopter was out on a maintenance test flight, which could point to a maintenance issue, he said.

"I am not going to make an assumption on the cause of the crash," Benson said, "but, certainly, investigators are going to be looking closely at the part they were testing."

A material failure would be something inherently flawed with the helicopter's engineering. Anything is possible, Benson said, but the UH-60 is a "stellar aircraft" with double and triple safety redundancies.

For now, the military is handling the investigation. The nation's primary accident investigator, the National Transportation and Safety Board, has not been called in to help, a NTSB spokesman said Friday. The NTSB investigates civil aviation incidents, but only steps in on military incidents upon request or if the aircraft had a civilian registration.

The U.S. military does not publish aviation accident data, but through a Freedom of Information Act request, Defense News compiled a database of all military aviation mishaps from 2011 to 2017. Of the 98 UH-60 Black Hawk mishaps reported during that time period on L-model and M-model Black Hawks — including combat and noncombat situations — about 25 could be related to mechanical problems, but only three resulted in significant damage or loss of life.

"For the amount of flight hours Black Hawks log worldwide, its mishap rate is actually relatively low," said Jen Judson, a Defense News reporter who monitors military aviation safety. "It's a very reliable aircraft."

UH-60 Black Hawk helicopters have been in use by the U.S. military since 1978. Today, the Black Hawk is primarily used as a transport vehicle, with the capacity to carry 11 soldiers. The UH-60 is used for a variety of purposes, including air assault, medical evacuations, command and control, stability and support operations.

Kristen Leigh Painter • 612-673-4767