By Kevin Smith, Staff Writer Sgvtribune.com

Posted: 01/07/2010 11:13:58 PM PST

A federal investigation is under way to determine the cause of a helicopter crash in the Sierra Nevadas that occurred Wednesday when the craft hit an unmarked Southern California Edison power line.

Three state scientists and the pilot of the Bell 206 helicopter were killed when the copter clipped a skyline grounding wire between two Edison transmission towers, igniting a fire that consumed the craft and sent debris flying.

The team had been conducting a deer survey in a craggy stretch of the mountain range where electric lines crisscross the canyons.

Edison spokesman Steve Conroy acknowledged the line wasn’t marked but said the utility was never asked to do so – by the FAA or any other agency.

“Those lines have been sitting up there since the 1950s when they were installed,” he said. “We’ve never been approached by any external parties, private or governmental, to install markers on the lines.”

Conroy said Edison transmission lines in the Antelope Valley and some other regions are marked, likely as result of construction guidelines in those areas.

“At the end of the day, we’re trying not to lose sight of these four people who lost their lives as a result of this,” he said. “It’s important for us to see the outcome of the investigation so we can determine what steps we need to take to avoid having this happen in the future.”

The investigation will likely consider such factors as line visibility, aircraft speed, a possible mechanical malfunction and pilot error.

“The FAA does not require that power lines be marked because we do not have authority over local developments/projects,” FAA spokesman Ian Gregor said in a statement. “However, we recommend that all power lines be marked to make them as visible as possible to pilots.”

And it would be the responsibility of the power line owner/operator to do that, he said.

The FAA offers the following recommendations”

Markers should be placed on transmission wires and support structures to minimize the chance that pilots could inadvertently fly into them

Markers on long wires across canyons, lakes and rivers should be at least three feet in diameter

Markers should be a bright color that’s easy to see, such as orange, white or yellow, as well as an alternating color scheme

Markers should be spaced about 200 feet apart in equal intervals (When lines are low to the ground or near an airport a closer spacing is recommended)

National Transportation Safety Board investigators will spend the next two weeks examining the wreckage and radar and air traffic control data, as well as interviewing eye witnesses before issuing a preliminary finding about the probable cause.

If it’s determined that SCE – a division of Edison International – shirked its duty to mark the power line, it could be held partially legally responsible for the crash, experts said.