The fog on Sunday morning near the scene of the crash was “as thick as swimming in a pool of milk,” said Scott Daehlin, 61. He was retrieving sound equipment for a Sunday service at his church in Calabasas when the sound of a helicopter coming low and loud through the thick marine layer caused him to look up.

“I couldn’t see anything, not even a silhouette,” he said Monday morning as he looked across the street where the steep mountainside rose. The grassy slope was littered in wreckage. “My first thought was, ‘What in the world is a helicopter doing out here in this fog?’”

For about 20 seconds, he said, he followed the sound of the helicopter as it swept over the church parking lot and south toward the crest of the Santa Monica Mountains. It sounded even and normal, but, he said, “it sounded too low.”

“It sounded almost like the pilot was hovering, trying to find his way,” he said. As the son of a pilot, he added, “I had a sinking feeling in my stomach, and I was saying, ‘Get some altitude.’”

Just then, the helicopter went down. He heard a loud thump and the crack of what sounded like fiberglass, and all sound from the engines stopped.

It turned out that the pilot, Ara Zobayan, who had held a commercial license since 2007, had not obtained a clearance to fly under instrument flight rules, which would have allowed him to navigate with the use of his instruments, officials said.

The special clearance from air traffic controllers allowed the pilot to fly through the controlled airspace around Burbank and Van Nuys, but it did not give him “blanket clearance” to continue on, an F.A.A. official said.