ALERT - Five people were rescued after their aircraft's right ski broke through the sea ice north of Alert on May 9.

The right ski of a Kenn Borek Twin Otter, like this one pictured outside of Iqaluit on April 15, broke through the sea ice north of Alert on May 9. - Kassina Ryder/NNSL photo

The pilots of the Kenn Borek Air Twin Otter believed the ice to be much thicker than it was when they attempted to land, said Sean Loutitt, vice-president, operations.

"They landed, they came to a stop and then one of the skis broke through the ice," Loutitt said. "It was much thinner than the crew thought it was from the air."

The plane was carrying two crew and three scientists conducting survey work, a report from Transport Canada said. The group was able to grab their gear and get out of the airplane before using a satellite phone to call the Kenn Borek base in Resolute Bay. They were taken to Alert by helicopter two hours later.

Half of the aircraft had sunk into the water by the time they were rescued.

"The aircraft fuselage (body) was last seen submerged up to the wings, tail high," the report said.

Loutitt said he does not yet know if the plane sunk completely or if it's still sitting on the sea ice.

"The weather has been quite bad so we haven't been able to get back to the site yet," he said.

"We need to get back to the site to assess how the aircraft finally settled onto the ice to determine how we're going to get it out of there."

Loutitt said the crew performed a manoeuvre to check the ice thickness before landing.

"They do what they call a ski drag, they come in and they land and then they take off again," he said. "They followed all the company procedures as far as establishing the site.

"The pilot had a lot of experience doing this before."

Loutitt said these incidents are rare.

"This is only the second time we've broken through the ice. The first time was 25 years ago right at the North Pole," he said.

Even so, landing on sea ice can be dangerous, he said.

"It is a risk that is out there," he said. "A person is trying to determine ice thickness and suitability from the air without being able to actually have somebody on the ground, so it is fairly subjective."

Ice can be unpredictable Loutitt said.

"They landed on a similar piece of ice half an hour before that 30 miles away and they drilled the ice and I think it was seven feet thick," he said. "You do get a lot of different ice."

Kenn Borek Air complied with Canadian aviation regulations and the Transportation Safety Board will not continue any investigation into the incident, according to an e-mail from Transport Canada.