On the night of Dec. 16, 1997, the crew of Air Canada Flight 646, a Canadair Regional Jet, conducted a Category I instrument landing system (ILS) approach to Runway 15 at the airport in Fredericton, New Brunswick, Canada. The ceiling and visibility were below the minimums published for the instrument approach. Nevertheless, the runway visual range on Runway 15 was 1,200 feet, and the crew was authorized by Canadian regulations to conduct the approach under these conditions. The captain saw the runway approach lights when the aircraft was 100 feet above decision height. The first officer, the pilot flying, disconnected the autopilot about 165 feet above ground level and the aircraft began to drift above the glideslope and left of the runway centerline. The first officer reduced thrust to idle in an attempt to recapture the glideslope. The captain believed that the aircraft was not in position to make a safe landing and commanded a go-around. The aircraft stalled during the go-around, struck the runway and then veered off the right side of the runway. The aircraft then struck a ditch, a hill and some trees, and came to rest approximately 1,130 feet from the runway. The captain and eight passengers were seriously injured; the first officer, the flight attendant and the remaining 31 passengers sustained minor injuries or no injuries. The Transportation Safety Board of Canada in its final report on the accident, said that the aircraft stalled at an angle-of-attack approximately 4.5 degrees lower than normal, and that the premature stall was caused primarily by a thin accumulation of ice on the wing leading edges. Many factors were involved in this accident: the weather, darkness, flight-crew training and aircraft knowledge, aircraft handling, aircraft operating procedures, aircraft performance and limitations, Canadian Aviation Regulations, runway lighting, distribution of information, aircraft design and certification, and overview of operations. The weather, with a low ceiling and low visibility in fog, was the one factor that led to the interaction of all the other factors and, finally, to the accident.4. What is the reason for the stall?