Flight and Events
Air Canada Flight 621, a Douglas DC-8-63 registered as CF-TIW, departed Montreal International Airport at 07:17 EDT on July 5, 1970. The aircraft carried 100 passengers, six cabin crew, and three flight crew. The flight to Toronto International Airport was routine. At approximately 10 miles from Toronto, the crew performed the In-Range Check. The Before-Landing Check, which includes lowering the undercarriage, was initiated about 8 miles out during the turn onto final approach. On this checklist, the item 'spoilers armed' was intentionally omitted.
The Incident
During the approach, a conversation occurred between the Captain and First Officer regarding whether to arm the ground spoilers 'on the flare' or 'on the ground.' They agreed that the First Officer would arm them 'on the flare,' just before touchdown. As power was reduced for the flare, the Captain gave the order 'OK,' and the First Officer immediately deployed the ground spoilers. However, the aircraft was still about 60 feet above the runway when the spoilers deployed, causing a rapid sink. The Captain exclaimed and applied full throttle to all four engines, pulling back on the control column to raise the nose. The First Officer apologized. Despite the Captain's actions, the aircraft struck the runway heavily, remained on the ground for about half a second, then bounced back into the air. As it rose, the ground spoilers began to retract.
Upon striking the runway, the number 4 engine and its pylon separated from the aircraft, falling onto the runway along with a piece of lower wing plating. This allowed fuel to escape and subsequently ignite. Damage was also sustained to the attachments of the number 3 engine, though that engine continued functioning.
The Crash Sequence
After the bounce, the aircraft climbed to approximately 3,100 feet above ground. During the climb, the First Officer communicated with the airport control tower, indicating the crew believed they could circle for another landing attempt on runway 32. However, about 40 seconds before the final crash, they realized the situation was irreversible. Throughout the climb, intermittent fire and smoke trailed from the aircraft.
Approximately two and a half minutes after the initial touchdown, the first explosion occurred in the right wing, outboard of the number 4 engine location, causing parts of the outer wing structure to fall. Six seconds later, a second explosion near the number 3 engine caused that engine and pylon to tear free, falling to the ground in flames. Six and a half seconds after that, a third explosion resulted in the loss of a large section of the right wing, including the wing tip. The aircraft entered a violent maneuver, with the right wing ablaze, losing height rapidly. More wing plating tore free, and the aircraft struck the ground at high velocity, approximately 220 knots, in a nose-low, left-wing-high attitude. All persons aboard were killed.
Probable Cause
The official investigation identified several contributing circumstances without weighting or ordering priority: the Captain's failure to follow the Before-Landing Check procedures regarding arming the ground spoilers; the First Officer's action, contrary to the Captain's order, of manually pulling the ground spoiler actuating lever to 'Extend' when the aircraft was about 60 feet above the runway; the manufacturer's failure to provide a gate or equivalent means to prevent inappropriate manual operation of the ground spoiler lever in flight; the Ministry of Transport's acceptance and approval of the ground spoiler system design; Air Canada's acceptance and use of the aircraft with this defective design feature; the failure of the manufacturer and Air Canada to unequivocally inform in their manuals that ground spoilers could be deployed in flight by such action and to warn of the hazard; the failure of Air Canada's Ground Training School to instruct pilots or warn of the danger; the failure of the Ministry of Transport to detect deficiencies in the manufacturer's flight manual and to require warnings; the failure of the Ministry of Transport to note differences between airline manuals and to take remedial action; and under overload conditions, the failure of the manufacturer to design engine pod attachments for safe sequential separation or to ensure fuel and electrical system integrity.