Tower Warned Pilot Before Fatal Crash : Investigation: Safety board says captain of the business jet might not have realized he was in the turbulent wake of a 757.

The pilot of a private executive jet that crashed Wednesday near an auto mall acknowledged a control tower warning that he was close behind another plane shortly before the crash, saying he had it in sight, an FAA spokeswoman said Friday.

But the pilot may not have known that he was following a United Airlines Boeing 757, a much larger airplane than the Westwind 1124 the pilot was flying. Crash investigators believe the 757 generated so much turbulence in its wake that it may have caused the private, 12-seat Westwind to roll out of control and plummet into a field next to several auto dealerships.

The crash killed two top executives of the In-N-Out Burger chain and three others aboard the Westwind, but no one was hurt on the ground. In-N-Out President Richard A. Snyder of Newport Beach and Executive Vice President Philip R. West of Irvine, who had broken their own rule about not flying together, died in the crash.

The National Transportation Safety Board continued Friday to focus on the issue of wake turbulence from United Flight 103, a Boeing 757 two miles in front of the Westwind.

Gary Mucho, regional director of the safety board, said it was unclear why the Westwind’s pilot, Stephen R. Barkin, was flying the aircraft 200 feet below instead of above the glide path of the Boeing 757, as most pilots are taught to do in order to avoid the wake of a larger aircraft.

FAA spokeswoman Elly Brekke said, “He acknowledged the controller’s statement about other traffic ahead of him, but it’s possible he didn’t know the other traffic was a 757.”

Regulations concerning air turbulence place almost all of the responsibility on the pilot to recognize its possible existence and take corrective action rather than require air traffic controllers to give out advisories, according to copies of the regulations supplied by the FAA.

Investigators did not release tapes of the controller or cockpit conversations Friday but said evidence indicates the Westwind was not assigned to fly at any specific altitude. Previously, safety board investigators said that radar recordings indicated the Westwind dipped about 200 feet below the bigger plane’s flight path.

Rules require a four-mile separation between a small plane and a large aircraft in situations where wake turbulence is possible, but that regulation does not apply because the Westwind and the 757 are both classified as large aircraft, officials said.

The two planes were more than three miles apart when the Westwind was cleared to land, the FAA’s Brekke said. “That meets all of the requirements,” Brekke said.

The safety board has estimated that the Westwind eventually closed to a distance of about two miles from the 757 just before the crash.

Mucho said investigators still have not ruled out catastrophic mechanical failure as a cause of the crash. The board’s technical staff was combing the wreckage Friday for clues, while their colleagues in Washington analyzed the cockpit voice data recorder from the Westwind’s cockpit. There was no flight data recorder, Mucho said.

Mucho estimated that it would take several days before a transcript of the voice recording is released. “We have to get all the parties involved to agree that it says what we think it says,” Mucho said.

National transportation safety officials said it is rare for a plane to crash because of turbulence from a jet. They could not say Friday how many crashes had been attributed to jet turbulence, but they identified two such incidents--one last year in Montana and another seven years ago in Van Nuys.

The Van Nuys crash occurred in May, 1986, killing the sole occupant of the plane, John Gibson, 37, a television actor. Gibson’s Socata Trinidad TB-20 crashed after it apparently struck the jet wash from a giant C-130 military transport plane that was landing just ahead of him.

Last year, seven people were killed when a Cessna Citation 550, owned by the U.S. Department of Energy, crashed in an industrial section of east Billings after crossing the wash of another jet.

Mucho said there was another incident this year in which a Boeing 737 following a 757 into Denver was apparently turned on its side while encountering the wake of the larger jet.

Also killed in Wednesday’s crash were Philip R. West, 37; Barkin, 46, the pilot; John O. McDaniel, 49, the co-pilot; and Richard Sims.

Times correspondents Jennifer Brundin and Mary Lou Pickel contributed to this story.