Stock wise, WS is a mature company whose stock has always been valued on the companies assets and performance/results. AC's stock has been volatile because of market suspicions on its ultimate performance after leaving bankruptcy protection and ACE's very model IPO pricing at under $2. At the time, while AC did have assets with a real value, it also had pension and other liabilities that had to be addressed. As these concerns have been addressed one-by-one, the stock has increased in value. And now, as restructuring and performance have achieved their goals -- along with the huge drop in fuel prices and thus operating costs -- the market looks more favourably on AC and this has resulted in a more realistic share pricing.

Further, WS is very restricted in its growth while AC has continued to employ its relatively new wide body fleet into international destinations. With the domestic/transborder markets pretty much saturated, WS's growth will only come from venturing more boldly into international destinations but this will be both expensive (new aircraft, overseas infrastructure and marketing) and time consuming. Thus its share price will only grow slowly compared to AC...though that airline's share growth will soon require a decision on dividend payments (which is another factor where WS is considered "mature" and off-sets continuing share price rises).

Yesterday's bump in AC's share price has likely brought it to a plateau for the balance of the year, and we know full 2017 performance patterns vs those of previous years based on the stabilizing of routes and aircraft assignment.