A flight safety system highlighted potentially serious problems with a Super Puma gearbox on two occasions before it crashed in the North Sea, an inquiry heard today.
Flight data downloaded from the ASS32-L2 showed that particles were detected on a gearbox part the week before the disaster.
Multiple epicyclic chip detection warnings were recorded on the Health and Usage Monitoring Systems (HUMS) on March 24th and March 25th.
The same warning was repeated on the HUMS device 15 minutes before the aircraft crashed off the coast of Peterhead, killing 16 people, on April 1.
Brice Fernando told a fatal accident inquiry that he analysed and decoded the flight data after the disaster.
The HUMS expert, who worked at the helicopter manufacturers Eurocopter at the time, said he had not been aware of the March 24th chip warning before the crash happened.
The inquiry was shown a graph which was described as a summary of chip detection on the epicyclic module.
Mr Fernando told the inquiry: “This graph shows there was particles detected on the 24th of March, the 25th of March and the 1st of April.”
Sheriff Principle Derek Pyle asked: “From your expertise with HUMS, are you able to say whether there is any connection with occurences on the 25th to the four occurences on the 1st of April?”
He replied: “No.”
The inquiry has heard that if particles are collected on an epicyclic chip detection system, it can be a warning of a problem with a gearbox part.
And if the chips remain undetected, the epicyclic module component could fail leaving the helicopter at risk of crashing.
The inquiry heard no chip detection warnings were recorded on the helicopter system between March 26 and March 31.
Mr Fernando dealt with a phone call from an engineer working for helicopter operator Bond on March 25th.
He told the inquiry that proper communication procedures were not followed by the engineer on that date.
The HUMS expert said engineers should fill out special forms with details of helicopter problems then email the form to the manufacturer.
The forms are then passed on to the appropriate manufacturing department.
However, the Bond engineer contacted him by phone on March 25th instead to ask for his advice.
Mr Fernando said staff from helicopter operators would not normally contact him by phone but they sometimes did if they were in a rush.
He said he was told that there was a problem with rising trends relating to the bevel gear component and a chip warning had come on for the epicyclic module.
He told the inquiry that the Bond employee informed him that maintenance staff had found a few particles in the bottom of the main gearbox.
The HUMS expert then contacted one of his colleagues for advice and said he had no knowledge of a chip having been found in the epicyclic module until after the crash.
He said he called Bond back with the information and spoke to another engineer who informed him that the particles had been considered “insignificant”.
It later emerged that the wrong work card had been followed due to the confusion between engineers and the manufacturing team on the gearbox location of the chip.
The aircraft was then cleared to fly with a work order raised for additional checks every 25 flying hours.
No further chips were detected.
The aircraft system recorded four further epicyclic chip detector warnings on the day of the crash on April 1, 2009.
The last one was recorded on the system 15 minutes before the fatal crash which was caused by a fatigue fracture of a second stage planet gear in the epicyclic module.
The inquiry continues.