DDDOF
When a tech stop is required, ANC is preferred over YVR. Generally it saves time and allows more payload to be carried over a tech stop in YVR. On eastbound flights during the winter the tracking may keep the aircraft further south to take advantage of the strong jetstreams that are present this time of year over the North Pacific. It is also worth noting that the flight is usually direct to YYZ from HKG because of this, this time of year. A tech stop is only required on the return to HKG in ANC. Once the summer schedule starts a tech stop is required in both directions.