A Super Puma that crashed into the North Sea killing 16 men was declared fit for service the day before the tragedy, an inquiry has heard.
The helicopter plunged into the water off the Aberdeenshire coast while returning from the BP Miller platform in 2009.
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A fatal accident inquiry (FAI) is being held before a sheriff in Aberdeen almost five years after the accident.
Fourteen oil workers and two crew were killed when the aircraft hit the sea on April 1.
Many of them worked for KCA Deutag Drilling and were returning from BP's Miller platform when the crash happened.
An investigation into the crash has found that the aircraft suffered a "catastrophic failure" of its main rotor gearbox.
James Gilmour, former engineering director at Bond Offshore Helicopters, gave evidence on the third day of the inquiry before Sheriff Principal Derek Pyle.
Technical logs for the helicopter were shown to the inquiry demonstrating that licensed engineers carried out scheduled maintenance the day before the fatal accident.
This included inspections of both engines and the personal locator beacons on the helicopter. After-flight inspections were also carried out that day, the inquiry was told.
Mr Gilmour, who now works as an aviation consultant, said: "There were no defects during the flights for that day."
Referring to the technical record of the work completed by the engineers, he said: "It has been signed off at the bottom saying the aircraft is fit for service."
Mr Gilmour told the inquiry there was an additional recurrent inspection (ARI) put in place for the helicopter gearbox on March 25 after the aircraft's chip detector picked up a magnetic particle.
The ARI ordered that the magnetic chip plugs of the gearbox be inspected at every shutdown of the aircraft for the next 25 flight hours.
The checks were carried out and signed off, according to documents shown to the inquiry.
"Nothing was found during all these inspections," Mr Gilmour said. "There were no chips found and the ARI was closed."
Fiscal depute Geoffrey Main, for the Crown, asked if Mr Gilmour was aware of the ARI at the time.
He said: "No, this is day-to-day work carried out in the hangar. I don't get involved down to that level."
He said he was not made aware of the discovery of the particle on March 25 until after the crash.
Mr Gilmour said he would not necessarily expect to have been told about the particle, stating it was "not that uncommon".
He said that in the hours and days after the accident, as investigators worked to discover its cause, the particle "wasn't high on my radar at that time".
A report by the Air Accidents Investigation Branch (AAIB) found that the gearbox failure caused the main rotor on the AS332-L2 model to break away and its ''tail boom'' got severed from the fuselage.
The inquiry at the Town House in Aberdeen is expected to last about six weeks and will examine the circumstances of the crash in order to prevent any future tragedy.
Captain and co-pilot Paul Burnham, 31, from Methlick in Aberdeenshire, and Richard Menzies, 24, from Droitwich Spa in Worcestershire, were killed with 14 oil industry workers.
Five men from Aberdeen died: Alex Dallas, 62, James Costello, 24, Stuart Wood, 27, Vernon Elrick, 41, and Brian Barkley, 30; and two workers were from Aberdeenshire: Leslie Taylor, 41, from Kintore, and Warren Mitchell, 38, from Oldmeldrum.
The other victims were Raymond Doyle, 57, from Cumbernauld; 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.
Some of the victims' families have expressed anger that there has been no criminal prosecution following the crash.
There have also been calls for a full public inquiry into helicopter safety to be held.
Documents shown to the inquiry indicated that the ARI was signed off by an engineer shortly after 6am on the morning of the crash.
Mr Gilmour agreed that the helicopter could not have flown on that day unless all related work orders for the aircraft had been completed and closed.
He is expected to continue his evidence to the inquiry tomorrow.
The fatal 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 this accident.
In May 2012 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.