A stunt plane piloted by top-rated WGN radio host Bob Collins crashed through the roof of a hospital and then exploded Tuesday afternoon in far north suburban Zion after colliding with a Cessna flown by a student pilot, killing all three people aboard the two aircraft but sparing scores of people on the ground, authorities said.

Investigating agencies and horrified witnesses gave conflicting accounts of the midair collision, which took place despite good flying weather: a clear sky and excellent visibility, on a relatively balmy February afternoon. Airborne collisions are one of the rarest causes of civil aviation accidents.

The National Transportation Safety Board said Collins' plane and the aircraft flown by the student pilot were in crowded airspace approaching the same runway at Waukegan Regional Airport around 3 p.m., the time of the crash.

David Bowling, air safety inspector for the North Central Regional Office of the NTSB, said the student pilot was on a supervised solo flight along with other planes around the Waukegan airport. She was doing traffic pattern work, Bowling said--taking off, traveling in established traffic patterns, landing and taking off again. He said he did not know how many planes were in the pattern.

Lake County Coroner Barbara Richardson confirmed that Collins, 57, an aviation enthusiast and private pilot for more than two decades, and his Mettawa neighbor, Herman Luscher, 58, a retired U.S. Navy pilot, died in the fiery crash. They were riding in Collins' Czech-made Zlin 242, a plane designed for acrobatic flying that friends said the popular radio host enjoyed for its high-performance sport capabilities.

The third victim, the student pilot, was at the helm of a Cessna 172, Richardson said. The woman's identity had not been released as of early Wednesday, although the coroner said the woman was a United Airlines flight attendant. The Cessna took off earlier Tuesday from Palwaukee Airport in Wheeling, officials said.

Investigators will analyze the wreckage and review air traffic radio tapes before deciding how to proceed.

Officials said it was too early to rule out mechanical problems or determine if the weather conditions somehow were factors in the crash. But a source at the safety board said investigators would focus on radio communications with the Waukegan tower to determine whether the pilots were looking out their windows frequently to stay far enough apart in the crowded airspace.

One witness said one of the planes hit the right wing of the other aircraft and they both plunged nose-first. "They were all tangled up and then they went down," said Randy Finck, who was part of a construction crew pouring concrete at a gas station.

The accident occurred at 3:04 p.m. when both aircraft were about two miles from touching down on Runway 23 at Waukegan's airport, said Carl Dinwiddie of the safety board.

"The planes were being sequenced to the runway, with the Cessna cleared to follow the Zlin," Dinwiddie said, adding that at least one air-traffic controller was on duty at the airport.

After the collision, witnesses said, Collins' white plane seemed to level off for a moment, then plunged and crashed into the fifth floor of Midwestern Regional Medical Center, 2501 Emmaus Ave., and exploded.

"It was a ball of fire," said Jim Leech, owner of a nearby insurance agency who ran outside after hearing the crash. "After about three minutes on the roof, it exploded."

The Cessna fell in the middle of Elim Avenue in a residential neighborhood after nose-diving into the parking lot of a senior citizens center. As the Cessna came down near the Sheridan Health Care Center, 2534 Elim Ave., the blue-striped plane clipped a tree, hit several cars and tumbled through some trees and bushes, according to witnesses.

At the cancer hospital where Collins' plane crashed, dozens of patients and employees were evacuated after the crash and explosion shook the facility, blowing out windows along the top floor. Two employees were slightly injured.

"I felt the whole floor move and there was an explosion," said Kathy Sutton, a hospital worker who was on the third floor.

Witnesses on the ground voiced shock and horror at what they had seen.

"I just saw it falling out of the sky," said Leo Barnes, who was standing in front of the Zion post office at Shiloh Boulevard and Sheridan Road. "I just stood there. I didn't believe it."

Tom Kane, a 16-year-old freshman at Zion-Benton High School, was home when he heard the collision. "I looked out my kitchen window into the sky and saw two airplanes breaking apart," Kane said. "The one plane nose-dived directly in the street in front of me. . . . I ran outside and I could smell gasoline really strong. I was scared and I didn't know what was happening."

Marla Becker, administrator of the Sheridan senior center, said she and about a dozen employees and residents ran out of the building after hearing the Cessna crash in the parking lot. The nursing home houses 210 senior citizens. None was injured.

"There was a small airplane in many pieces in the middle of the street," she said. "There was debris all over. The plane was mangled. The cockpit was in the middle of the street and a wing and a tire were on the front lawn."

Collins was rated as a single-engine pilot and passed his most recent medical exam in November 1996, according to Federal Aviation Administration records. Collins carried a Class 2 medical certificate, usually issued to charter pilots, corporate pilots and anyone else who flies commercially.

Tom Petersen, news director for WGN radio, said Collins was a cautious but enthusiastic pilot who kept an office at the Waukegan airport to spend more time close to his hobby. When he went up, though, Collins usually flew with a flight instructor. "That was one thing he was adamant about," Petersen said. "He believed in that whole-heartedly. . . . He was absolutely terrific (as a pilot)."

Collins, a member of the Experimental Aircraft Association, which sponsors the Oshkosh Air Show each summer, co-owned the 4-year-old Zlin with Daniel A. Bitton, president and chief executive officer of DB Aviation in Waukegan.

"Mr. Collins was a close and dear personal friend of mine as well as being a safe and capable flying partner," Bitton said.

Luscher flew regularly, according to neighbors, serving as pilot or co-pilot. He will be remembered for his involvement in village affairs and for his friendly demeanor, neighbors said.

"He was a good friend," said Jack Tindall, who lives across the street and down the block from Luscher. "He also was active in civic affairs, and we will miss his involvement in our village. . . . He was a wonderful person, a very fine man."

Luscher is survived by his wife and a young son, neighbors said.

Aviation Training Enterprises, a flight school based in Ronkonkoma, N.Y., owned the Cessna, according to FAA records. Attempts to reach officials from the flight school were unsuccessful.

Authorities were trying to determine Tuesday night the extent of the student pilot's flying experience. A student pilot must fly a minimum of 40 hours in training, including at least 10 hours of solo flight time, to earn a private pilot certificate. The requirement had been 20 solo hours, but was changed in 1997.

Even experienced pilots must overcome the blind spots inherent in the design of their aircraft. The Cessna 172 has a high wing over the top of the fuselage, obstructing the view above and behind the cockpit. The Zlin 242 is a low-wing monoplane with a canopy, making it difficult to see directly below the aircraft.

Midair collisions are rare in general aviation, accounting for 18 accidents last year out of 39 million flights, according to the Air Safety Foundation of the Aircraft Owners and Pilots Association. Midair collisions, however, tend to occur mainly when weather conditions are clear and favorable to visual flight rules. In addition, the foundation said, 49 percent of midair collisions occur when aircraft are approaching or departing an airport.

Seven people were killed in July 1997 when a Cessna 172 flown by a student pilot collided with a Beechcraft Bonanza near Meigs Field. The NTSB determined that both pilots failed to see and avoid the other plane.

The airspace in the area follows visual flight rules, which means it is the responsibility of all pilots to see and avoid all other traffic, as well as maintain two-way radio contact with the tower, said FAA spokesman Bob Handschiegel.

He declined to say how many controllers were working at the Waukegan tower, which is staffed by a private air-traffic control company hired by the FAA. Handschiegel also said he had no information whether either plane radioed the tower with problems.

Richard Stephenson, chairman of the board of Midwestern Regional Medical Center, said the center offers specialized cancer treatment and is affiliated with Cancer Treatment Centers of America. Stephenson said he and Collins used to ride their Harley-Davidson motorcycles together.

"When I heard it was him . . . I broke down, quite literally. It was a real jolt," Stephenson said.

Robert L Collins