Flights of a helicopter that crashed into the North Sea killing 16 men were temporarily halted a week before the accident when a problem was discovered with its gearbox, an inquiry has heard.
Fourteen oil workers and two crew died when the Bond-operated Super Puma plunged into the water off the Aberdeenshire coast while returning from the BP Miller platform on April 1 2009.
Verner Hill, an engineer and deputy shift supervisor with Bond at the time, said he was "unhappy" and "uneasy" after a problem was detected in the aircraft days before the tragedy.
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Mr Hill, 54, who now works as a fleet support specialist with Bristow Helicopters, was giving evidence at a fatal accident inquiry at Aberdeen's Town House.
He was on duty on March 25 2009 when a colleague flagged up a problem with the helicopter's health and usage monitoring systems (Hums) during a turnaround inspection after the aircraft's first flight rotation that day.
The helicopter had flown from Aberdeen to the Unity platform in the North Sea, returning at 8.20am.
Mr Hill said data downloaded from the Hums showed a purple flashing warning light on the main gearbox indicator that appeared to indicate its chip detector had picked up a particle of metal.
The issue was only discovered after the helicopter had taken off on another flight at 9.25am, the inquiry heard.
Mr Hill said that at the time there was no requirement for Hums data to be fully downloaded and examined before a helicopter took off again, but that was now standard procedure.
He said he spoke to his line manager about the problem after further checks were carried out and no more anomalies were found.
"I was asking whether we needed to recall the aircraft from flight, if I remember correctly," he said. "I wasn't told to recall it."
He was shown a report prepared after the fatal crash which, he told the inquiry, appeared to indicate that the particle had been detected 94 times.
When the helicopter returned at 11.40am, Mr Hill and another colleague carried out an inspection on the main gearbox and no particles were found, the inquiry heard.
But an examination of the Hums after the helicopter's second flight still showed the warning.
Mr Hill said he was "uneasy" with the situation.
"I wasn't happy with what I was seeing," he said. "I spoke to the oncoming supervisor about it. I can't remember who decided but we took it offline.
"It was due to go on a training flight but we took it off the training flight and put it into the hangar for an after-flight inspection to be carried out."
The inquiry heard that a particle was later found during the after-flight inspection.
Asked why it was not found earlier, Mr Hill said: "I've thought about this and the only thing I can think of is I missed it because of whatever reason, bright sunlight, I don't know."
The particle may also have been caught up in the chip detector's O-ring when it was taken out of the gearbox, he added.
The inquiry previously heard there was an additional recurrent inspection (ARI) put in place for the helicopter gearbox in the days following the detection of the 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.
It was signed off and closed on the morning of the fatal crash, the inquiry has heard.
An investigation into the crash has found that the aircraft suffered a ''catastrophic failure'' of its main rotor gearbox.
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 crash claimed the lives of captain and co-pilot Paul Burnham, 31, from Methlick in Aberdeenshire, and Richard Menzies, 24, from Droitwich Spa in Worcestershire.
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.
The inquiry before Sheriff Principal Derek Pyle is expected to last about six weeks and will examine the circumstances of the crash in order to prevent any future tragedy.
Solicitor advocate Tom Marshall, who represents many of the families of those who died, later renewed a motion for the technical logs of all Bond helicopters being operated on March 25 to be released to the inquiry.
"It's simply a question of how much work the engineering staff had to contend with," he said.
But Sheriff Principal Pyle refused the motion, stating that there was no evidence that errors were made because of "pressure of business".
Information about other helicopters was therefore not relevant to the inquiry, he said.
"There's no suggestion that they (the engineering staff) failed in some way to investigate and identify the fault for the helicopter with which we are concerned," he said.
But he added that questions remain about events on March 25 after the gearbox fault was discovered.
He also revealed that he had decided it was "not right" for him to read the AAIB report into the crash.
Sheriff Principal Pyle said: "It is undoubtedly the case that, thus far, the big question of this inquiry is what on earth happened on the 25th?
"It appears - and, as I said, I haven't read the AAIB report - there is a bit of uncertainty about why this helicopter fell into the sea.
"It is understood it was the gearbox, we all understand that, but we really don't know, there is no certainty, about exactly why the gearbox failed.
"There are theories about it. Things can't be discounted and it may relate to what happened on the 25th."
The inquiry continues on Monday.