FREDERICK, Md. (AP) — Federal investigators were at the scene Friday of a collision between an airplane and a helicopter near a Maryland airport that killed three men but spared two others in the plane.

The two who survived deployed a parachute to slow the aircraft's descent.

The National Transportation Safety Board is leading the investigation into what caused the Cirrus SR22 plane and a Robinson R44 helicopter to collide Thursday in the air. Investigators were combing the scene and planned to talk with survivors and air traffic controllers.

The plane went down in a line of trees east of downtown Frederick, while the helicopter crashed a tenth of a mile south of the plane, between two storage units, Maryland State Police spokesman Greg Shipley said.

The plane, which hit a stand of trees, appeared to be largely intact, but the helicopter was demolished.

All three men aboard the helicopter were killed. They were identified as Christopher Parsons, 29, of Westminster, Maryland; Breandan McFawn, 35, of Cumberland, Maryland; and William Jenkins, 47, of Morrison, Colorado. It's unclear which of them was piloting the helicopter.

The pilot of the airplane, Scott Graeves, 55, of Brookeville, Maryland, and his passenger, Gilbert Porter, 75, of Sandy Spring, Maryland, were treated at a hospital in Hagerstown and released Thursday evening, according to state police.

Messages left at the homes of Graeves and Porter were not immediately returned Friday.

The Federal Aviation Administration said the helicopter was in a training exercise when the collision occurred, though the agency did not provide specifics. The plane was coming in for a landing.

The helicopter was leased to Advanced Helicopter Concepts, a flight school at the airport.

Chris Hollingshead, who identified himself as an employee of the flight school, said Friday that the company was voluntarily suspending flights and cooperating with investigators.

"Hopefully this investigation will prevent this type of horrible accident" in the future, he said.

Hollingshead said Parsons was an experienced flight instructor with the company and that Jenkins was on board to see if everything was in order for it to be rented out. Hollingshead said McFawn was a passenger but did not make clear whether Parsons or Jenkins was flying the helicopter. He did not answer questions.

The company's website says Parsons decided to become a helicopter pilot during his service in the U.S. Marine Corps, where he worked on helicopters for five years, and was looking forward to helping students begin their own careers as helicopter pilots.

"This is a horrible day," Hollingshead said. "We're all shocked and horrified."

A helicopter of the same make and model, also operated by Advanced Helicopter, crashed in 2009 on Interstate 70 about 15 miles west of Frederick, killing all four people aboard. The NTSB ruled that crash an accident due to poor nighttime visibility on a fog-shrouded mountain. The weather Thursday was cloudy and breezy, and NTSB senior air safety inspector Brian Rayner said it did not seem to be a factor in the crash.

A transcript of the control tower conversation provided by LiveATC.net indicates the tower was working with two airplanes and three helicopters shortly before the crash.

"I have three helicopters below you in the traffic pattern," the controller tells an inbound airplane.

"I have two of 'em in sight," the pilot responds.

The controller then gave the airplane clearance to land. In the next second, the audio is overtaken by someone screaming, "Oh, God! Oh, God!"

Jesse Ault Jr. of Brunswick, Maryland, and his wife, Pamela, saw the airplane "spiraling out of control" before the crash, and said the pilot was hurt and shaken up.

"The pilot had blood up above his nose and on his face," Ault said. "You could tell he was visibly shaken."

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Associated Press reporter David Dishneau contributed to this report.