Transport Canada issued an emergency airworthiness directive regarding wing to fuselage attachment joints on DHC-8-400 aircraft models.
Transport Canada reports that there have been three in-service reports of cracked barrel nuts found at the front spar locations of the wing to fuselage attachment joints. Additionally, three operators have reported finding a loose washer in the barrel nut assembly. Failure of the barrel nuts could compromise the structural integrity of the wing to fuselage attachments.
Preliminary investigation determined that these cracks are due to hydrogen embrittlement.
The AD mandates an initial and repetitive detailed inspection of the barrel nuts. The AD applies to all DHC-8 aeroplane models 400, 401 and 402, serial numbers 4001 and subsequent that have accumulated 1900 or more total hours air time or 12 months or more in service since new