A paperwork anomaly may have emerged in technical logs over the maintenace of a Super Puma helicopter that crashed into the North Sea killing 16 men, a fatal accident inquiry has been told.

The claim was made by a former engineering director of the aircraft's operators, Bond Offshore Helicopters, at the hearing into the tragedy that occurred as the workers were returning from a BP platform off the north-east coast.

James Gilmour told the hearing in Aberdeen yesterday there seemed to be a discrepancy in maintenance records on the aircraft the day before the crash.

He insisted the company had enough staff on shift on March 31 to carry out the required work.

The inquiry was shown ­technical logs demonstrating checks carried out on the helicopter that day were completed between 9.30am and 9.40am.

Solicitor advocate Tom Marshall, representing many of the families of those who died, said the timeframe "did not seem feasible".

The inquiry heard yesterday an additional recurrent inspection (ARI) was put in place for the helicopter gearbox on March 25 after the aircraft's chip detector picked up a magnetic particle.

The ARI ordered the magnetic chip plugs of the gearbox be visually inspected at every shutdown of the aircraft for the next 25 flight hours.

Mr Gilmour told the inquiry that in the 10-minute window the ARI had to be carried out and the aircraft refuelled with 1140kg of fuel. A pre-flight inspection was also required.

He said he did not believe that 10 minutes was long enough for all the work to be carried out.

Mr Gilmour said: "It would take longer to shut down and start up the aircraft, and the window for refuelling doesn't seem right to me.

"I would have thought you would at least need 15 minutes. .

"It appears it's a 10-minute window, but it seems a very small window to do all three tasks. There is an anomaly there, I think."

Sheriff Principal Derek Pyle said a test may need to be carried out to check the time it would take to refuel the aircraft and establish the correct time the engineers had to carry out the work.

Mr Marshall also questioned the number of engineers on shift the day before the fatal crash. "Four men looking after eight helicopters seems quite a low number," he said.

Mr Gilmour said: "With the rosters we have, when the aircraft are actually flying we have turnaround inspections. I would say that was a good number to have involved in that."

Maintenance staff were also on call if there was a problem with any aircraft, he added.

An investigation into the crash has found the aircraft suffered a "catastrophic failure" of its main rotor gearbox.

A report found the gearbox failure caused the main rotor to break away and its "tail boom" got severed, killing Paul Burnham, 31, Richard Menzies, 24, Alex Dallas, 62, James Costello, 24, Stuart Wood, 27, Vernon Elrick, 41, and Brian Barkley, 30; Leslie Taylor, 41, and Warren Mitchell, 38. Other victims were Raymond Doyle, 57, David Rae, 63, Gareth Hughes, 53, Nairn Ferrier, 40, James Edwards, 33, Nolan Goble, 34, and Latvian Mihails Zuravskis, 39.

The inquiry continues