RENO, Nev. --

Investigators said the pilot of a medical helicopter issued a mayday moments before the aircraft crashed into a hilly area north of Reno near the Nevada-California state line early Saturday.

All three crew members - the pilot, flight nurse and paramedic - were killed.

The helicopter, an Aerospatiale AS350, had dropped off a patient at a Reno hospital and was returning to its base in Susanville, Calif., when it crashed around 2 a.m. Saturday, according to Federal Aviation Administration spokesman Ian Gregor.

A witness driving on a nearby road told authorities he saw nothing unusual about the helicopter's flight before it fell rapidly from the sky. The witness said he saw a fireball when the helicopter hit the ground, according to Gregor.

Gregor said the pilot was not communicating with air traffic controllers at the time of the accident. Investigators from the FAA and National Transportation Safety Board spent Saturday combing the wreckage about 29 miles northwest of Reno in Lassen County as they searched for clues about the cause of the crash.

The wreckage will be taken to a salvage yard Sunday.

The helicopter was operated by Mountain Lifeflight out of Susanville. The company confirmed the loss of all three crew members aboard the helicopter. Mountain Lifeflight issued a statement Saturday afternoon identifying the pilot as James Bradshaw, 39, the flight nurse as Clinton Reger, 40, and Christopher Ritz, 37, as the paramedic.

It was the second fatal crash of a Mountain Lifeflight helicopter returning to Susanville after dropping off a patient at Renown Medical Center in Reno.

According to the National Transportation Safety Board, a Eurocopter AS-350B operated by the company crashed into Honey Lake, about 11 miles southeast of the company's Susanville base, on March 21, 2002. NTSB investigators determined the pilot failed to maintain altitude and said the smooth surface of the water contributed to pilot disorientation.

The pilot died in the crash and two crew members were seriously injured.