Air Canada flight 621 was a routine early morning flight originating from Montreal-Dorval International Airport, QC (YUL), with destination Toronto International Airport, ON (YYZ). The DC-8-63 plane, a relatively new airplane which had been delivered just over two months ago, departed at 07:17 for a flight which was to take just over 50 minutes. The captain was pilot flying. The enroute and descent portion of the flight were uneventful. At a distance of 8 miles from Toronto Airport, about 08:02, the “Before-Landing Check” was made. This included the lowering of the undercarriage and according to Air Canada procedures should include arming the spoilers. This item however was intentionally omitted. On previous flights were the captain and first officer had flown together they had disagreed on when to arm the spoilers. Both men did not like to arm the spoilers at the beginning of the final approach, fearing that this increased the chance of inadvertent spoiler activation. The captain preferred to arm the spoilers on the flare, while the first officer preferred to arm and extend them on the ground. Although both procedures where contrary to company policy, it was agreed between them that when the captain was flying the aircraft, the first officer would cause the spoilers to be extended on the ground, and when the first officer was flying the captain would arm the spoilers on the flare. However on this particular occasion, the captain and first officer had a discussion about when the spoilers should be armed. The captain finally ordered: “All right, give them to me on the flare”, which was contrary to their personal agreement on previous flights. Power was reduced then on the aircraft for the purpose of the flare and the captain gave the order to the first officer by saying “O.K.”; and immediately thereafter the ground spoilers were deployed. The aircraft was about 60 feet above runway 32 at that time and began to sink rapidly. The captain immediately noticed what had happened, applied full throttle to all four engines and pulled back the control column. The nose came up as the aircraft continued to sink. Realizing what he had done, the first officer apologized to the captain. The plane than struck the runway heavily, causing the number 4 engine and pylon to separate from the wing. It fell on the runway along with a piece of the lower wing plating, allowing fuel to escape and subsequently ignite. The DC-8 rose back into the air, at which time the ground spoilers retracted, and climbed to an altitude of 3100 feet. During this climb, fire and smoke were seen trailing behind the aircraft intermittently. The crew wanted to circle for an emergency landing on runway 32. This was not possible because of debris on the runway, so the controller suggested a landing on runway 23. About two and a half minutes after the initial touchdown an explosion occurred in the right wing outboard of the number 4 engine location causing parts of the outer wing structure to fall free to the ground. Six seconds later, a second explosion occurred in the vicinity of number 3 engine and the engine with its pylon ripped free of the wing and fell to the ground in flames. Six and one half seconds later, a third explosion occurred which caused the loss of a large section of the right wing, including the wing tip. The airplane then went into a violent manoeuvre, lost height rapidly and at the same time more wing plating tore free following which the DC-8 struck the ground at a high velocity, about 220 knots in a left wing high and nose low attitude. PROBABLE CAUSE: The Canadian investigation report did not conform to ICAO standards and did not contain a probable cause as such.