Approaching Sioux Lookout runway 16 after a flight from Red Lake the Metro collided with a Piper PA-31-350 Navajo Chieftain (C-GYPZ) operated by Air Sandy. The Piper aircraft had just taken off from Sioux Lookout runway 34 and was climbing through 4500 feet on its way to Red Lake when its right wing collided with the Metro’s right wing. The accident happened in daylight (13:30 LT) with a visibility >15 miles and a 8000 feet cloud base. PROBABLE CAUSE: “Neither flight crew saw the other aircraft in time to avoid the collision. Contributing to the occurrence were the inherent limitations of the see-and-avoid concept which preclude the effective separation of aircraft with high closure rates, the fact that neither crew was directly alerted to the presence of the other aircraft by the Flight Service specialist or by onboard electronic equipment, and an apparent lack of pilot understanding of how to optimise avoidance manoeuvring.”