The cabin crew ran up to the flight deck as passengers screamed, said Bruce Northrup, a New York City banker returning from a wedding with his wife and 15-year-old son. "People were yelling, `Tell us what's going on,"' he said in an interview with The Associated Press.
The twin-engine jet made a U-turn and began descending gradually. The pilot told the 300 or so frightened passengers they had a "serious technical problem" and were headed to Shannon, Ireland, a half-hour away. He also told them to calm down.
They were quiet, but not calm, for what turned into a very long 90 minutes, Northrup said. After a safe emergency landing, passengers saw what had caused the problem: a windshield covered with cracks.
"That window looked like something out of an automobile junkyard," Northrup said.
Boeing officials traced the problem to faulty wiring in a window heater. At least two other Boeing 777s have experienced the same problem in the past year, the AP has learned. All landed safely and no one was hurt.
Experts say three similar incidents in one year is unusual for an aircraft.
The 777, Boeing's newest, largest twin-engine jet, is among the most modern in the commercial fleet. It entered service in 1995, carries up to 550 people and costs between $153 million and $231 million each, depending on the model. There are 138 registered in the United States, according to Federal Aviation Administration records.
Their windshields, made of three layers of glass, acrylic and epoxy, can get brittle in the cold, thin air at cruising altitude seven miles up. They're warmed by a heater to stay elastic. The wires on the three planes that suffered cracked windshields loosened and shorted out.
On the Alitalia flight, the short caused a small fire and the innermost layer of the window cracked, Boeing spokeswoman Liz Verdier said.
The flight crew put out the fire with an extinguisher in three seconds and then brought the plane down to 10,000 feet. That reduced the difference between the pressurized cockpit and the thin air outside, said Bill Waldock, aviation safety professor at Embry-Riddle Aeronautical University in Arizona. The danger at high altitudes is that the windshield could shatter and loose items or people could be sucked out, though that's never happened on a commercial flight.
Boeing has sent a directive to airlines instructing them how to tighten the wire connections. Boeing also is developing circuit breakers that will prevent sparking and the window from overheating, Verdier said.
Fires can be a bigger safety issue than cracked windows.
"Electrical fires are kind of nasty because they're so hot," said Waldock. "But as long as that's all there is, it's the easiest to stop."
John O'Brien, safety director for the Air Line Pilots Association, said the wiring problem in the 777s isn't a major concern because the embedded filaments in the windshield are isolated from other combustible materials.
FAA officials said Boeing is taking appropriate action.
"Anytime there's a fire, there's a concern to us," FAA spokesman Paul Takemoto said. "But cracked windshields rarely affect the safety of the aircraft."
Most windshield damage is caused by planes striking birds. Between Jan. 1, 1990, and last Dec. 31, there were 442 such incidents recorded by the FAA's National Bird Strike Database. However, database manager Sandra Wright estimates 75 percent of bird strikes go unreported.
Waldock said it's extremely rare for a cracked windshield to cause a major problem for pilots. If the crack is serious enough the pilot simply descends and makes an emergency landing at the nearest airport, as the Alitalia crew did.
Waldock said to his knowledge the most serious incident involving a windshield occurred 13 years ago over England when the captain's front panel of a BAC-111 cracked and blew out as the plane was cruising at 20,000 feet.
"He started out of the airliner," Waldock said of the pilot. A member of the flight crew managed to grab his legs, and two stewards clung to him for 15 minutes while the co-pilot made an emergency landing.
"They landed with him out the front end," Waldock said.
By Leslie Miller