Operators of Bombardier Challenger 600s are being instructed to carry out repetitive operational tests of the flap-control system following an uncommanded flap-extension incident.

The root cause of the incident remains under investigation, says Transport Canada, but the tests have been ordered as an interim mitigation.

Transport Canada states that the incident involved the uncommanded deployment of flaps, from zero to 45°, during climb.

The aircraft’s crew received a ‘flaps fail’ caution message and the jet returned to the departure airport without further incident.

“Investigations found that the flap-control system failed to arrest the uncommanded movement due to a failed retract relay,” says Transport Canada in a directive.

“The failed retract relay also caused the flap-control system to operate at half-speed and this was undetected during previous flights.”

Challenger incident-c-Anna Zvereva Creative Commons

Source: Anna Zvereva/Creative Commons

UK investigators are probing a flap-extension incident on a Challenger 604

While the regulator has not given specific details of the event, UK investigators are probing such an incident which occurred to a Challenger 604 departing Farnborough on 10 August last year. The jet had been climbing through 19,000ft and travelling at nearly 300kt when the flaps extended.

The checks are aimed at verifying functionality of the retract relays.

Transport Canada says operators must carry out the initial operational test of the inboard and outboard flaps within 100h or 15 months, and conduct repeat tests depending on the aircraft variant and the intervals laid out in Bombardier service documentation.