The account was given on the first day of a Fatal Accident Inquiry almost five years after the Super Puma plunged into the water off the Aberdeenshire coast.
Lidvar Olav Hildre, a ship's mechanic, was painting a railing on board the Normand Aurora, a platform supply boat sailing to Norway. The inquiry, sitting at the Town House in Aberdeen, was told he heard a helicopter making a "normal buzzing noise" above the ship.
"Apart from the helicopter noise I didn't hear anything else - then suddenly there was silence," he said in a statement to police that was read out by Fiscal Depute Geoffrey Main, appearing for the Crown before Sheriff Principal Derek Pyle.
Mr Hildre's statement continued: "This made me look into the air, as this was unusual, and I saw on the starboard side of us an oblong shape falling like a torpedo towards the sea."
The weather was good with clear conditions and a calm sea, he said.
"The object was obviously a helicopter, but I couldn't believe what I was seeing.
"It fell silently towards the sea. I don't think there was any smoke or anything coming from the helicopter at that point.
"Just before the helicopter hit the sea, or just as the helicopter hit the sea, I cannot be sure which, I saw one flame come from the helicopter. I couldn't say exactly where on the helicopter this came from.
"There was then a big splash as the helicopter hit the sea in a bang, then there was white smoke.
"After this I then saw, quite clearly, four large black rotor blades all attached together falling out of the sky towards the sea, separate from the helicopter.
"The rotor probably hit the sea around the same place as the helicopter but I never saw it hit."
He heard a bigger bang as he ran to report what he saw to his superiors, who prepared to launch a fast boat.
Debris was spread in pieces around an area about 300 feet in diameter.
Details of the search were relayed to him on board the Normand Aurora.
Eight bodies were on the surface, tied together by rescuers to prevent them floating away.
As the only eyewitness account was read out, family members in the public gallery sat silently, some wiping tears from their eyes.
Fourteen oil workers and two crew were killed when the aircraft hit the sea on April 1, 2009.
Many of them worked for KCA Deutag Drilling and were returning from BP's Miller platform when the helicopter's main rotor gearbox suffered a "catastrophic failure".
The first witness called was Malcolm Paterson, 29, a Bond Offshore Helicopters mechanic who worked on the aircraft before it left on its final journey.
He explained the process and said nothing unusual was noted by anyone involved before it was signed off.
The inquiry, expected to last about six weeks, will examine the circumstances of the crash and make recommendations in an attempt to prevent any future tragedy.
Some of the victims' families have expressed anger that there has been no criminal prosecution following the crash.
Lorraine Doyle, father of Raymond Doyle, from Cumbernauld, told The Herald last week she was "sickened" by the decision by the Crown Office and Procurator Fiscal Service.
The inquiry began with a roll call of all 16 victims, with their names, occupations and some personal details read out.
Captain and co-pilot Paul Burnham, 31, from Methlick, Aberdeenshire, and Richard Menzies, 24, from Droitwich Spa, Worcestershire, were killed along with Mr Doyle and 13 other workers.
Five men from Aberdeen died: Alex Dallas, 62; James Costello, 24; Stuart Wood, 27; Vernon Elrick, 41; and Brian Barkley, 30. Two workers were from Aberdeenshire: Leslie Taylor, 41, from Kintore, and Warren Mitchell, 38, from Oldmeldrum.
The other victims were David Rae, 63, from Dumfries; Gareth Hughes, 53, from Angus; Nairn Ferrier, 40, from Dundee; James Edwards, 33, from Liverpool; Nolan Goble, 34, from Norwich; and Mihails Zuravskis, 39, from Latvia.
A report by the Air Accidents Investigation Branch said the gearbox failure caused the main rotor on the AS332-L2 model to break away and its "tail boom" was severed from the fuselage.
The crash happened just six weeks after a Super Puma EC225 ditched as it approached a production platform owned by BP. All 18 people on board survived that accident.
In May last year the same model of helicopter, destined for an oil platform, went down about 30 miles off the coast of Aberdeen and its 14 passengers and crew had to be rescued.
Five months later another EC225 carrying an oil crew from Aberdeen to a rig 86 miles north-west of Shetland was forced to ditch. The 17 passengers and two crew were rescued from life rafts by a passing boat.
New advice on checks for the EC225 model were issued following the accidents.
Four oil workers were killed when their Super Puma L2 plunged into the sea off Shetland on August 23 last year. Fourteen people survived.
The inquiry continues.