NTSB details final moments before deadly mid-air collision involving Pennsylvania police helicopter

CARLISLE, Pa. -- The National Transportation Safety Board has released its preliminary report on last month's mid-air collision involving a Pennsylvania State Police helicopter and a Cessna aircraft at the Carlisle Airport in Cumberland County.

Federal investigators said the Aug. 19 crash occurred just before 7 p.m. as the Cessna was approaching the runway to land. The helicopter had already landed and exited the runway but was hovering in a nearby field.

According to the NTSB, the helicopter crew was conducting a training flight and returning to Carlisle Airport when they became aware of the approaching Cessna.

A witness who heard radio transmissions between the aircrafts told investigators the helicopter crew instructed the Cessna pilot to "extend his downwind," meaning to continue flying parallel to the runway to create additional spacing between aircraft. The pilot of the Cessna acknowledged the instruction, the report said.

One of the helicopter pilots told investigators the crew received a traffic collision avoidance system alert before spotting the airplane and communicating over the radio. The Cessna pilot had also advised that he was second in line to land.

Airport surveillance video reviewed by investigators showed the airplane crossing the runway threshold about 30 seconds after the helicopter crossed it and while the helicopter remained near the airfield.

According to the report, the airplane never touched down. Instead, it continued along the runway before pitching up and beginning to climb.

"After the airplane reached the apex of its climb, about 1 wingspans above the runway, the right wing dropped and the airplane immediately turned right and descended toward the northwest," the NTSB report states.

Investigators said the helicopter was hovering about 50 feet north of the runway when the airplane leveled its wings, rapidly pitched up and struck the rear section of the helicopter, hitting the tail rotor and main rotor blades.

The NTSB said only about eight seconds elapsed between the time the helicopter exited the runway surface and the collision.

The helicopter crew told investigators they were unable to see the approaching Cessna before impact because it was behind them.

As a result of the collision, the Cessna broke into four pieces, while the helicopter's rotor and tail blades separated from the aircraft.

Investigators recovered all major wreckage components and flight data from both aircraft.

Post-crash examination of both aircrafts revealed no evidence of any pre-impact mechanical malfunctions or failures that would have precluded normal operation.

Both pilots aboard the Pennsylvania State Police helicopter suffered injuries but have been released from the hospital.

The pilot of the Cessna, identified as Dr. Paul Sokoloski, 57, of Hershey, Pennsylvania, was killed in the crash.

The NTSB's investigation continues.

Read the full preliminary report here.

ABC News contributed to this report.