Canada’s fleet of Sikorsky CH-148 Cyclone helicopters have returned to limited flying following a two-month grounding, after a software issue was detected with the aircraft’s flight control computers.

An investigation by the manufacturer found the software problem affects all the Cyclone aircraft. An update to eliminate the issue will be in place before Block 2 deliveries begin, says Sikorsky, but the firm, fixed-price contract covering the programme ensures that no costs will be borne by the customer.

The software issue will cause a one-month delay for aircraft training, but the Royal Canadian Air Force expects initial operational capability for the CH-148 will remain on schedule for April 2018.

“Based on the root cause of this particular issue, the fix is 100% software,” says Doug Baker, project manager for the maritime helicopter programme. “From that perspective, too, that makes the retrofit fairly straightforward.”

The RCAF's 12 Wing at its Shearwater base in Nova Scotia has five helicopters being used for operational training and evaluation, with a number having returned to the manufacturer for the Block 2 update. Sikorsky will deliver four more between now and the end of the summer for a total of 14 Block 1 aircraft. The first six Block 2 types are still scheduled for delivery in June 2018, with all 28 helicopters to arrive by 2021.

The RCAF expects Sikorsky will have the software fix retrofitted for aircraft stationed at 12 Wing and Block 2 production line models by late 2017, Baker says.

After grounding the fleet in early March, Sikorsky flight-test aircraft resumed sorties on 27 April and five Canadian helicopters stationed at Shearwater returned to flight on 16 May. The rotorcraft initially began flying as the investigation progressed, a Sikorsky spokesman says.

After discovering the flight-control issue, the RCAF resumed some flight testing with the most severe restrictions impacting operations at low speeds close to the ground, says Colonel Peter Allan, 12 Wing commander. The service could not hoist personnel, sling cargo, execute sloped landings, practice manoeuvres close to the ground or take off and land on ships, he says. That left operators with the ability to depart from the training base at Shearwater to maintain currency and basic point-to-point navigation.

“We still managed to progress some testing from that flight posture,” Allan says. “High-level surveillance missions where we’re not manoeuvring close to the ground but we’re still able to employ a bunch of our tactical systems to support any kind of an operation.”

While Shearwater lifted the most severe restrictions on 9 June, to return to hoisting and shipboard operations, limitations on induced pitch and roll remain. Those restrictions only apply at certain altitudes and modes of the flight-control system, Allan says.

“So we can still do those manoeuvres, just in different modes than we might otherwise have done them,” he says. “It’s more of a technical restriction and avoiding certain pieces of the code really in the software, making sure we don’t induce a fault, but Sikorsky has narrowed down very specifically what pieces of the code are affected in the software and how we would induce those pieces of code to be triggered.”