Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:
Several operators have reported cases of inadvertent single spoiler deployment during flight on the DHC-8 Series 400 aircraft. Investigation has revealed that the probable cause for this deployment is internal contamination of the Lift/Dump (L/D) valve and moisture ingress into the L/D valve armature.
This condition, if not corrected, could cause uncommanded deployment of the spoilers resulting in increased drag and in combination with a loss of aileron, could result in a significant reduction in aircraft roll control.
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.