The safety agency has released a report into the June 2012 accident, which also raises concerns about non-approved equipment that had been installed on a self-righting system aboard the boat and concludes survival suits used during the exercise were inadequate, leaving two surviving crew members with mild hypothermia.
The incident happened on June 3 of last year, when a four-member crew was conducting a training exercise on a Zodiac Hurricane rigid-hull, inflatable fast-rescue craft on Sechelt Rapids, a narrow channel off Sechelt Inlet, located northwest of Vancouver, that is known for large rapids and strong currents.
The crew were members of the Royal Canadian Marine Search and Rescue, a volunteer search-and-rescue group that operates throughout B.C.
The rescue craft, named the Lewis-McPhee, was heading through Sechelt Rapids to conduct a navigating and towing exercise with another vessel, the Ken Moore.
The Lewis-McPhee arrived early and the crew decided to conduct another exercise, known as station keeping, in the rapids while they waited for the Ken Moore, the safety board report says.
About 10 minutes after entering the rapids, a wave from the left side of the boat caused the vessel to roll and then capsize.
Two crew members were thrown clear of the boat, but two others, Angie Nemeth and Beatrice Sorensen, became trapped underneath.
Two nearby boats responded to the crew's distress calls, and a Cormorant search-and-rescue helicopter also headed to the scene. One of the surviving crew members attempted to activate the Lewis-McPhee's self-righting system, but the system — which the safety board says used parts that had not been approved by the manufacturer — did not work.
About 45 minutes after the boat capsized, two search-and-rescue technicians dove into the water and located Nemeth and Sorensen, but by then, the two crew members had no signs of life. Their vests were caught on the overturned boat, and the search-and-rescue technicians were unable to free them.
The capsized boat was towed to a government dock a short distance away, where a shore crane was used to lift the Lewis-McPhee out of the water. Paramedics on scene pronounced Nemeth and Sorensen dead.
The two surviving crew members, meanwhile, suffered mild hypothermia and reported difficulty staying afloat in the rapids.
The Transportation Safety Board was unable to identify what exactly caused the rescue craft to capsize, but the report noted that because the crew decided at the last minute to conduct the station-keeping exercise and that they did so without an advanced plan and without considering the potential risks involved.
The safety board report notes that guidelines for the B.C. coast recommend station-keeping exercises should only be conducted during periods of "slack water," when there is little or no tidal currents. The crew started the station-keeping exercise at approximately 11:20 a.m., but the next period of slack water wasn't expected until after 2 p.m., the report says.
The report also suggests the training was unnecessary.
"The location chosen ... for the station-keeping exercise was well known for its standing waves and strong currents, and was selected to help train the crew members to provide SAR (search-and-rescue) aid to those trapped within the rapids," the safety board report says.
"However, SAR statistics for the past nine years do not indicate that there has been a need for this type of rescue in the rapids, because the swift water carries persons swept overboard downstream, as in this occurrence. If high-risk training exercises are carried out without consideration of the need for training, proper planning and preparation, risks to crew members are increased."
The crew members were wearing anti-exposure suits, but their suits were inadequate for the conditions, the report notes.
"The coxswain (the crew member in charge) and surviving crew member were found to be suffering from mild hypothermia when they were rescued," the report says.
"The marine anti-exposure suits they were wearing did not provide sufficient thermal protection, nor did they provide adequate buoyancy while the crew members were in the cold and turbulent waters of Sechelt Rapids."
The Transportation Safety Board subsequently issued a number of safety memos related to the self-righting system used on the Lewis-McPhee, warning operators of fast-rescue crafts to only use parts that have been approved by the manufacturer.
Royal Canadian Marine Search and Rescue responded to the crash by prohibiting training on the rapids and restricting travel on the rapids to emergencies only.
The organization also directed that all of its vessels with self-righting systems be serviced to ensure only approved parts were used and that all such vessels be re-certified.
Jim Lee, president of Royal Canadian Marine Search and Rescue, said his organization implemented a new training program soon after the tragedy.
He said safety remains his group's primary focus, and the organization would be examining the safety board's report to determine whether other steps should be taken.