Air accident investigators have made a number of fresh safety recommendations after finalising a joint report into two offshore helicopter ditchings in 2012.
The measures include a tightening-up of regulations on liferafts to ensure that they deploy correctly in the event of an emergency.
The European Aviation Safety Agency (EASA) will also be asked to review the way in which the devices are installed.
Crew and passengers on both the EC225 Super Puma flights, which were ferrying workers to North Sea platforms, were rescued after pilots made controlled landings.
The first Bond-operated aircraft, with 14 people onboard, ditched about 30 miles off the Aberdeen coast while on its way to the Maersk Resilient rig on May 10, 2012.
In the second incident, all 17 passengers and two crew escaped injury when a CHC-operated helicopter went down about 32 miles south of Shetland on its way to the West Phoenix drilling rig on October 22, 2012.
In both instances, a 360-degree crack formed in the gearbox shaft.
An emergency lubrication system was deployed during both flights, which should have allowed the aircraft to return to base.
However, a warning light came on, prompting the pilots to ditch the helicopters immediately.
It has emerged that “incompatibility” problems with the aircraft wiring and pressure switches led to the light coming on unnecessarily.
The final Air Accident Investigation Branch (AAIB) report into the two non-fatal ditchings, officially published today, said the warning light would “always” come on after the crew activated the emergency lubrication system.
It also states that Eurocopter had “underestimated” the maximum stress the gearbox shaft could take when testing the part.
However, the report acknowledges that the safety of the key component was still “adequate”, providing there was no corrosion.
Super Puma manufacturer Airbus – formerly Eurocopter – has made a number of safety improvements in response to the two incidents and two fatal crashes, in 2009 and 2013.
Working jointly with the industry and operators, Airbus has designed a new shaft for the EC225, which has been certified and is due to be installed in all of the North Sea fleet.
However, the AAIB has also recommended that new cockpit checklists should be introduced, similar to those which are used on fixed wing aircraft.
There are several safety checks regarding liferafts on the helicopters that have been recommended.
On the Bond-operated flight, investigators found the liferafts were slow to deploy, while on the CHC flight, lines to one of the rafts became entangled.
The report advises that liferaft manufacturer Survitec should provide clear instructions on the installation of the emergency aids.
The EASA is also tasked with ensuring the liferafts operate as intended.
The report says the agency should “ensure that there is a high degree of deployment reliability in forseeable sea conditions”.
It further recommends that EASA should develop “certification requirements” for liferafts mounted on the outside of helicopters.
Finally, the EASA will also be asked to carry out research into the “fatigue performance” of components made from high-strength, low alloy steel.