UPPER DARBY, Pa. (AP) — Federal investigators say they have been unable to determine what caused a medical flight to go haywire before the helicopter crash-landed without losing any lives nearly two years ago.

The pilot somehow avoided a web of power lines and buildings as it came out of a nose-dive, slamming sideways to the ground next to a church in suburban Philadelphia.

The National Transportation Safety Board said in its final report dated Jan. 4 that the Eurocopter EC135 was flying from Chambersburg toward a Philadelphia hospital at an altitude of about 1,500 feet when it abruptly increased its altitude and then went into a steep dive over Drexel Hill.

The pilot was able to recover from what surveillance video showed was a “near-vertical, nose-down, spiraling descent” but “was unable to climb or hover” due to insufficient engine power, and the aircraft crashed, the safety board said.

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The helicopter, owned by Denver-based Air Methods, part of the LifeNet program based in Hagerstown, Maryland, was transporting an infant girl, the pilot and two medical crew members when it came down at about 1 p.m. on Jan. 11, 2022 next to Drexel Hill United Methodist Church in Upper Darby. The pilot was seriously injured.

The safety board said the probable cause was “an inflight attitude upset for undetermined reasons” that resulted in over-speeding of the rotor system and a reduction of power from both engines, which were functioning as designed but left insufficient power to continue normal flight.

“Examination of the helicopter revealed no evidence of malfunction that would result in an abrupt departure from cruise flight,” the safety board said.

The flight medic said he and the flight nurse were out of their seats treating the patient when there was a loud “bang,” the helicopter banked sharply and rolled, and the two were then “pinned to the ceiling.” Later, the aircraft leveled, and they were able to secure the patient and secure themselves in their seats before bracing for the landing.

The pilot told investigators in September 2023 that he did not recall the beginning of the emergency, but remembered fighting for control, then “assessing and rejecting multiple forced landing sites before selecting the point of touchdown,” the report said.

Upper Darby Fire Chief Derrick Sawyer said there were children in a day care associated with the church at the time of the crash. Upper Darby Police Superintendent Timothy M. Bernhardt called it a “miracle” that there were no life-threatening injuries.