Description

On 3 January 2019, a Bombardier DHC8-400 (C-FSWE) being operated by WestJet Encore on a scheduled domestic flight from Calgary to Nanaimo as WEN3109 and in the cruise at FL 220 lost prescribed separation in day VMC against a privately-operated Piaggio P180 (N990RS) flying from Spokane to Kamloops at the same level as their tracks converged. In the absence of any ATC intervention, the DHC8 received and actioned a resultant TCAS RA to DESCEND which subsequently restored the prescribed minimum separation between the two aircraft. 

Investigation

An Investigation was carried out by the Canadian Transportation Safety Board (TSB). It was quickly apparent that the two aircraft involved had been flying in accordance with their respective clearances prior to the avoiding action taken in response to the TCAS RA which had been the sole action taken which resolved the loss of separation. Sufficient relevant recorded ATC data and testimony was available to enable a detailed reconstruction of the events leading up to the conflict so no recorded information or crew experience details were sought in respect of the two aircraft involved. Rather, the focus of the Investigation was on the failure of ATC to ensure that clearances which maintained prescribed separation were issued.