PENSACOLA, FLA., DEC. 28 -- Investigators climbed aboard a crippled Eastern Airlines jet today seeking to learn why it cracked open after a hard landing Sunday night in foggy rain and dragged its tail section 7,000 feet down a runway.

Three of the 105 people aboard the DC9 suffered minor injuries during an emergency evacuation, and were treated and released at two hospitals. Flight 573 originated in Richmond and passed through Atlanta.

The twin-engine plane remained on the runway today with a two-foot crack circling its fuselage between the wings and engines.

Several passengers said they expected the worst after the plane slammed onto the runway. "I thought it would crash and burn," passenger Tyrone Taylor said. "I knew we were coming too fast. We hit real hard."

{One point of the probe by the National Transportation Safety Board is the Pensacola Regional Airport's Instrument Landing System (ILS), which tells pilots the angle of their glide approach to the runway, United Press International reported.

{Drucella Anderson of the NTSB said the jet was cleared for an ILS approach, but the tower told the crew the system was in alarm, meaning it may not be working.

{"The crew responded they were receiving normally," Anderson said.}

The jetliner dragged its fractured tail section the length of the 7,000-foot runway, stopping within 50 yards of the far end at 11:40 p.m., said Chuck Porter, the airport's acting manager.

"It's very unusual," Fred Farrar, a spokesman for the Federal Aviation Administration in Washington, said of the accident. "The only other one even similar to it was several years ago."

In that accident, the tail section of an MD80, an enlarged version of the DC9, broke off behind the rear-mounted engines after a certification flight.

The jet landed Sunday night in rain and fog, and visibility was only two miles while the ceiling was 900 feet, said Jack Barker, an FAA spokesman in Atlanta. But he said he was unsure if weather was a factor.

The plane's captain was a 20-year veteran pilot, Eastern spokeswoman Karen M. Ceremsak said. She refused to identify him. Eastern officials said they were unsure whether the plane could be salvaged.

As the jetliner scraped down the runway Sunday, passengers were told to put their heads down, passenger Carolynn Fleming said. "All of us I'm sure were just thinking the plane would stop before the fire started and fortunately the fuel lines stayed intact," she said.