An elderly man with a heart condition was shocked when a bolt from a Boeing jet flying overhead plunged through the roof of his Sydney home.

"I used to go hunting. I used to shoot rabbits. I know the noise a gunshot makes. This is worse than a gunshot," homeowner Angelo Margiotta said on October 18.

Mr Margiotta said he was sitting in the kitchen of his home at Five Dock, in Sydney's inner west, when he heard a "big, big, big, loud bang" just before 9am (AEST).

Firemen called to Mr Margiotta's home found a damaged roof tile and a bolt in the ceiling space.It appeared to them to have been... a high-speed impact," a fire brigades spokesman said.

The Civil Aviation Safety Authority (CASA) later confirmed the 10cm bolt came from a Boeing jet either landing or taking off from Sydney airport that morning.

CASA will now try to find out which aircraft the bolt fell from.

It said the bolt was most likely used to attach the mechanism that extends and retracts a plane's wing flaps, which happens mainly when planes take off and prepare to land.

CASA officials obtained the serial number from the bolt once firemen arrived at the scene.

"It is an aircraft bolt manufactured in America," CASA spokesman Peter Gibson said.

"It is used on a number of different types of Boeing aircraft and used in a number of locations including the wing flaps.

"The next question is what plane does it come from and that's not quite as easy."

Mr Gibson said no aviation safety issues had been reported in relation to the missing bolt, believed to be one of several which operate the wing flaps.

"We don't have any immediate serious safety concerns," he said.

CASA has determined the bolt is not made by Boeing but by a company that supplies parts for Boeing aircraft.

Qantas has all but been ruled out of the search since it sources parts directly from Boeing, Mr Gibson said.

Similar debris from the sky has struck Sydney homes twice in the past 10 years but the material turned out not to come from planes, he said.

(Editor's Remark: Later reports indicate the bolt belonged to a Singapore Airlines' Boeing 747 aircraft)