US and Canadian safety authorities have issued an urgent update on how pilots should inspect the wings of Bombardier CRJ100 and CRJ200 regional jets in cold weather operations before take-off, and how those take-offs should be accomplished.

A Federal Aviation Administration final airworthiness directive is due to take effect on 21 April, three weeks after a similar emergency AD issued by Transport Canada became effective.

 © Bombardier

The new rule replaces a 2005 AD that called for flight manual changes to counter stall-related loss-of-control issues on take-off due to "even small amounts of frost, ice, snow, or slush on the wing leading edges or forward upper wing surfaces", according to the FAA.

Since that time, the FAA says it has learned from Transport Canada of three new "uncommanded roll during take-off" incidents involving both regional jets and the business jet sister, the Challenger.

The FAA is now proposing new temporary revisions to the aircraft flight manual dealing with limitations and procedures for cold weather or icing conditions. Included are new tactile inspections for ice on wings limitations and procedures for using wing and cowl anti-ice during taxi and take-off and modified take-off guidelines to reduce high-pitch attitudes during rotation.

The FAA says Transport Canada is developing "further actions", including crew awareness and training, and further rulemaking is possible.