Investigators are working to determine why a small plane veered off course while landing at a rural Pennsylvania airport and collided with a hovering state police helicopter, killing the plane’s pilot and injuring two state troopers.Aaron McCarter, investigator-in-charge with the National Transportation Safety Board, said Thursday there was no immediate explanation for the fatal crash.“Many of you have all seen the videos that have turned up online. It’s very dramatic. That shows the collision. We see the outcome, but we want to understand why it happened,” McCarter said.Investigators will examine the wreckage, aircraft, pilots’ actions and weather and other environmental conditions at the time of the crash.Plane struck helicopter during landingThe crash at the small airport in Carlisle, about 110 miles (170 kilometres) northwest of Philadelphia, involved a Bell 407 helicopter and a Cessna 150, according to the Federal Aviation Administration.The Cessna was attempting to land when it veered to the side and collided with the rear of the police helicopter, which was hovering above a grassy area beside the runway during a training exercise, Pennsylvania State Police said.The plane struck the helicopter’s tail, killing the Cessna pilot and sending both aircraft crashing to the ground.Investigators examine pilot communicationMcCarter said both pilots were flight instructors. The airport did not have a control tower, but pilots communicate over a common frequency.He said communication had been established between the two flight crews and investigators have strong evidence that the Cessna pilot was aware of the helicopter hovering nearby.However, investigators have yet to determine whether the helicopter may have been difficult for the pilot to see.“I can’t tell you whether or not his visual acuity or whether or not the helicopter was blocked from view,” McCarter said.Mechanical issue also being examinedMcCarter said the Cessna pilot had carried out maintenance on the aircraft before the flight, but investigators do not yet know whether a mechanical problem contributed to the crash.He said the aircraft’s flight path was unusual and investigators are examining why it approached from that direction before making a sudden turn.“I have no information at all to tell me either pilot of either vehicle was at fault. We are very early in the investigation to determine that,” McCarter said.Pilot killed, two troopers injuredThe plane’s pilot was identified as Paul William Sokoloski, 57, by the Cumberland County Coroner’s Office. He was the only person aboard the Cessna.The helicopter lost its blades and tail boom before crashing on its side. Both pilots were trapped inside until one pushed out a window and helped the other escape, Lt. Col. George Bivens, the state’s acting police commissioner, said at a news conference Wednesday night.“When I say it was a very violent crash, that plane was cut into a lot of pieces,” Bivens said.The helicopter was piloted by Cpl. Bryce Corman and Trooper Jason Mills. Both were airlifted to Penn State Health Milton S. Hershey Medical Center.Corman has since been released, while Mills remains in hospital with a good prognosis, Pennsylvania Governor Josh Shapiro said Thursday.