Federal investigators spent Thursday scouring the rooftop of New Mexico’s only top-level trauma center in search of clues as they tried to determine what caused a medical helicopter to crash while taking off from the roof.

Neither the pilot nor the two crew members on board were seriously hurt in Wednesday’s crash, but the damaged helicopter remained on its side Thursday atop University of New Mexico Hospital. Part of its tail section was still hanging over the edge of the six-story building.

Investigators with the Federal Aviation Administration and the National Transportation Safety Board inspected the wreckage and interviewed people who were on the ground at the time of the crash.

Some witnesses had reported a gust of wind before the chopper went down. But Brad Deutser, a spokesman for PHI Air Medical, the company that owns the aircraft, said it’s too soon to say what might have contributed to the crash.

“At this point, there’s lot of speculation, but that’s the whole purpose for the investigation — to find out what really happened,” Deutser said. “We wish we had the exact answer so we could address it, but the FAA and NTSB have taken the lead on the investigation so we can get the facts.”

No patients were aboard the chopper when it went down. The crew had just dropped off a patient and was leaving when the crash occurred.

Images from TV news helicopters showed the roof around the wrecked chopper soaked as firefighters sprayed the tail section with water, but no flames were visible.

Within a couple of minutes of the wreck, the emergency sprinklers surrounding the helipad were activated, and hospital personnel pulled the pilot and two crew members from the craft, hospital spokesman Billy Sparks said.

“Everything worked as it should, and first responders did an amazing job,” Sparks said. “We are extremely fortunate that no one suffered major injuries and that no patients or employees were injured.”

The hospital’s fifth and sixth floors were evacuated as a precaution, but operations had returned to normal by Thursday, Sparks said.

A team with the Federal Emergency Management Agency worked overnight to make structural improvements to four damaged roof joists, Sparks said. Structural engineers have been monitoring the building and have determined it is stable.

It’s unclear how long the hospital’s helipad will be out of service, but Sparks said an alternate landing zone has been identified.

Two of PHI Air Medical’s three bases in New Mexico are back up and running, and the third is expected to resume service by next week. Deutser said the company employs 40 pilots, flight nurses, paramedics and mechanics in the state.

The pilot, whose name has not been released, has worked for the company for more than 10 years. Deutser said he’s a highly experienced pilot.

The wreck at the hospital, in a busy area just north of the university, comes just weeks after a news helicopter crashed at an intersection near Seattle’s Space Needle, killing both people on board. That crash prompted Seattle officials to review policies about permitting helipads.