During the night flight, the pilot was cleared through Class Bravo airspace and he queried the controller if there was an altitude restriction on his route. The controller stated that he must remain at or below 500 feet and that a frequency change was approved upon reaching a local geographical reporting point (Century Boulevard). A review of radar data disclosed that the helicopter followed an interstate southbound toward the destination airport. The radar data further showed that about 3 minutes prior to the last target, the helicopter's altitude varied between 200 and 400 feet mean sea level (msl). The last target was observed at a mode C reported altitude of 400 feet msl (about 250 feet above ground level), and located adjacent to Century Boulevard. Several witnesses reported observing the helicopter flying low southbound along the interstate. They then recalled seeing a bright spark as the helicopter collided with a high voltage transmission line, followed by the helicopter impacting the asphalt. The main wreckage, consisting of the fuselage and engine, came to rest in the far left lane of the seven-lane southbound side of the interstate. The wreckage was located almost immediately above Century Boulevard, which extended perpendicular (and under) the interstate. Power lines were located adjacent to the wreckage with two major steel support tower structures on either side of the interstate. Neither the towers nor the wires had obstruction markings or lights, nor were they required to have any. The wires were oriented east-west and the highest wires measured about 120 feet in height; the most southern static wire contained a 6- to 8-inch abrasion in the galvanized steel, consistent with the helicopter's skid making contact. There was no evidence of mechanical malfunction or failure found during the postaccident examination.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

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