Another problem identified during the investigation was that a fail-safe system, including valve position indicators and gas pressure sensors, was not installed to alert the crew when a valve failed.
Wärtsilä shipped Ferguson’s main engines in early 2017 without such monitoring systems, although the company later installed them as standard on new engines and installed them on the ship’s smaller auxiliary engines.
The CalMac report suggests that standards body Lloyds Register may have approved the system on the assumption that such safety features were fitted to all engines.
These sensors are now installed on the Glen Sannox and will also be installed on its sister vessel MV Glen Rosa, due for delivery later this year.
The failed valve was replaced with a new model, and CalMac provided additional training to its personnel. The vessel is not currently powered by gas.
In a statement, CalMac said: “Following the incident in June 2025, lessons have been learned and corrective action taken.
“The vessel is absolutely safe to operate on LNG, and the decision not to refuel her with gas after her annual overhaul at the beginning of the year was solely due to our desire to return her to service as quickly as possible.”
The Marine Accident Investigation Unit reviewed CalMac’s report and indicated that it was satisfied with the firm’s actions to correct the situation.
Wärtsilä said client confidentiality prevented it from answering questions about why fault-tolerant monitoring equipment was not installed at Glen Sannox or who had access to its service notifications.
The statement said: “We are committed to sustainable development and maintaining the highest standards of safety, quality and reliability for our customers.
“We work closely with our customers throughout the lifecycle of our solutions and provide technical guidance, updates and support where needed.”