An engine tailcone fell off a Delta Air Lines jet shortly after takeoff Thursday and plummeted thousands of feet before landing harmlessly on a lawn in a Long Island residential neighborhood.

Apparently, neither the pilots nor anyone on the ground immediately noticed the mishap when it happened. The aircraft, a Boeing 777, doesn't need the part to fly and carried on safely to its destination, Tokyo, aviation officials said.

Delta personnel reported the engine part missing following an inspection after the plane landed following its 14-hour flight, Federal Aviation Administration spokeswoman Arlene Salac said.

The 20-pound cone, measuring 4 feet long and 3 feet in diameter at its widest spot was big enough to kill someone if it hit them from a great height.

It was on the lawn of a home in Roosevelt, N.Y., for several hours before anyone called police. The house is about 9 1/2 miles east of Kennedy Airport, where the flight originated.

Delta spokesman Anthony Black said an investigation is under way to determine what went wrong. He said he was unaware of any similar problems involving Boeing 777s in Delta's fleet.

A Boeing spokeswoman said she had no information about the accident.

A similar mishap involving a tailcone dropping off a Boeing 777 in mid-flight was reported in Japanese newspapers in 2005.

There were 206 passengers and 15 crew aboard Thursday's flight, according to the airline.