Washington ? Alitalia Flight 610 was over the Atlantic on its Rome-to-New York flight last July when the Boeing 777 seemed to shudder. Passengers smelled smoke.

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.

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.