Eurocopter has begun dispatching kits for the interim fixes needed to put its EC225 helicopter back into operations.

Around 80 EC225s of the 157 EC225s and military EC725s delivered have been grounded since October due to issues with the bevel gear vertical shaft that forced the ditching of two aircraft into the North Sea last year. A series of interim fixes were approved by the European Aviation Safety Agency (EASA) as well as the U.K. Civil Aviation Authority on July 9, with the kits being sent to operators the next day. The modifications are yet to be approved by Norway authorities. A decision from Oslo is expected on July 12.

The kits are being applied to all of the remaining 157 aircraft, while those on production lines in France and Brazil will have the modifications retrofitted before the aircraft are delivered to customers.

Jean-Brice Dumont, Eurocopter’s head of engineering, said the fallout from the problems has affected other parts of the company. “We had to take resources away from working on the EC175 and EC225 modernization and maturity to work on the EC225 gearbox,” Dumont said in an interview with Aviation Week. “We have taken many long-term lessons from the impact of these problems.”

More than 100 engineers have been working on the problems since the grounding began in October. Dumont said there had been many “false eureka moments” until a major breakthrough in the root cause was made in late February.

Engineers had managed to explain the cause of what had happened to the shaft fitted to the Bond Offshore aircraft relatively quickly, according to Dumont. But the problems were less clear on the shaft of the CHC aircraft,which had endured many more hours of flight time when it failed last October.

The main interim fix is a modification to the EC225’s health and usage monitoring system (HUMS), known as M’ARMS. Mod 45, as it is known, collects real-time data from accelerometers near the vertical shaft, monitoring for exceedances. If these indicate the presence of a crack, the system will signal the pilot, who then has a 2-hr. margin to land at a location where maintenance can be performed.

Aircraft without a HUMS will be dependent on the use of ultrasonic non-destructive inspections every 8-11.5 hr. Dumont says engineers should be able to fit the aircraft with the fixes within a week, although no operator has confirmed when they will return the aircraft back to operations.