Residents say the area around Las Virgenes Road was covered in fog at the time. The little valley is effectively the upper end of Malibu Canyon, which climatologists say could channel marine moisture through the mountains.
Stephen LaDochy, a climatology professor at Cal State L.A. who has studied marine layer movements, said that conditions can change abruptly in the uneven Southern California terrain.
"You have competing things going on at the same time," he said. "The inversion layer is heavier, drier air sinking down, while the marine layer is pushing up. It is a battle zone between the uplift and the sinking motion of the marine layer."
Beker, the pilot, said clouds will also roll right over the mountaintops, creating a swell. He said Zobayan appears to have been flying just above the cloud tops, which can be disorienting. "It's really easy to get tricked," he said. "You don't have a horizon."
He said at this angle it would be hard to notice any upward curve of the cloud deck where it rode over the mountains. "Suddenly you're in the cloud."
Zobayan climbed from 1,250 feet to 2,125 feet, slowing down to 126 mph. Then he veered south and plummeted.
Aviation consultant William Lawrence, a retired Marine Corps colonel and helicopter test pilot and instructor, said the S-76B's steep climb and rapid descent probably was triggered by the pilot's sudden realization that he was too close to the ground.
In addition to a warning from air traffic control that he was too low to be seen on radar, the pilot also might have been alerted by a ground proximity warning system telling him to pull up, Lawrence said.
Deetz said the aircraft was outfitted with such a device. It would squawk "Terrain! Terrain! Terrain!" in a high-pitched voice if the craft came close to the ground or an obstacle. He said the alert was triggered so often by high-rise buildings that pilots sometimes shut off the audio.
As the helicopter rapidly rose into the clouds in a "zoom climb," Lawrence said, the pilot could have become spatially disoriented as he peered from the helicopter to get his bearings, a condition involving the inner ear that can result in the inability to tell up from down. In some instances, pilots trying to level their aircraft have wound up "punching the nose over" and sending it plummeting into the ground.
"Spatial disorientation can happen really, really quick," said Lawrence, a seasoned accident investigator, noting that pilots are trained to react by relying on their instrument readings.
"The only way you live is to pay attention to your instruments," Lawrence said.
It's also possible that the helicopter experienced a mechanical malfunction that resulted in the pilot's loss of control, he said.
Jerry Kocharian, 62, was standing outside the Church in the Canyon drinking coffee when he heard a helicopter flying unusually low and seeming to struggle.
"It wasn't sounding right, and it was real low," Kocharian said. "I saw it falling and spluttering. But it was hard to make out as it was so foggy."
The helicopter vanished into the sheet of fog, then there was a boom and "a big fireball," he said.
"No one could survive that."
(Times staff writers Richard Winton and James Rainey contributed to this report.)
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