Canada's half-century-old Sea King helicopters will take a step closer to retirement next month, with the last official East Coast flight planned for Jan. 26, CBC News has learned.

West Coast operations will continue until December 2018, military officials said, at which point the new Cyclone aircraft will officially take over as Canada's Maritime helicopter.

There still may be some Sea King flights on the East Coast past January, but only for logistical reasons, such as repositioning the aircraft locally or sending them to other parts of the country.

Sea Kings have been operating in Canada since 1963.

The multipurpose workhorse aircraft is paired with every Royal Canadian Navy frigate. Its tail and rotors fold so it fits inside the ship. Its hull is designed to perform emergency water landings, and it can be outfitted as a submarine hunter, with sonar systems and torpedoes.

Cyclone helicopters still being tweaked

The Sea King's replacement is the Cyclone, a military variant of the Sikorsky S-92.

The federal government has accepted delivery of more than a dozen Cyclone aircraft, but not all of them are currently in Canada.

A Canadian military Sikorsky CH-148 Cyclone conducts test flights with HMCS Montreal in Halifax Harbour on April 1, 2010. (Andrew Vaughan/Canadian Press)

Each new batch of helicopters is flown and tested by Canadian aircraft experts. If changes are needed, the helicopters are sent back to Sikorsky to re-enter the production cycle and the improvements are made for future versions.

There have been at least three different batches or "blocks" delivered to Canada.

New issue discovered

The navy recently discovered a new problem with the latest block of Cyclones.

Just like the Sea Kings, these helicopters are designed to land on ships at sea. To test the Cyclone's limits, the crew of HMCS Montreal spent months seeking the worst weather and highest seas.

Life at sea is fun...but it's no joke! Cyclone helicopter remains firmly attached to MONTREAL's deck during trials. <a href="https://t.co/uDx72CKO0q">pic.twitter.com/uDx72CKO0q</a> —@MapleSeaLeaf

In extreme conditions, the Cyclone can use a cable to safely land on a ship. While the helicopter hovers above the surging and tilting vessel, the cable slowly winches the aircraft down.

The method is highly effective, but officials found it can cause problems for another important system.

The Cyclone is also equipped with a sonar system that it lowers into the water on a tether. It dips beneath the surface and sends out pings to search for submarines.

Sonar could hit ship during landings

"Analyses have shown that, in theory, it is possible for the sonar submersible unit to contact the ship-mounted assisted-recovery system when operating in high sea state condition," said an emailed statement from Department of National Defence officials.

Put simply, both the sonar and landing systems work fine. But due to the sonar's position, it could hit the ship when the helicopter uses the cable landing system.

The long-term fix will be to reposition the sonar system. Until Sikorsky makes that change, the current group of helicopters can either be used as shore-based aircraft, or have the sonar system removed for ship-based operations.

Even without the tethered sonar system, the Cyclone can still search beneath the surface. An additional sonar system sends remote buoys into the ocean that transmit acoustic information wirelessly back to the helicopter.

The next block of Cyclones will fix the sonar issue by repositioning the mechanism. That block should be delivered by June 2018.