On July 5, 1970, an Air Canada plane crashed while landing in Toronto, (Ontario). All 108 passengers and crew died.
Captain Peter Hamilton and First Officer Donald Rowland had certainly flown together before. But they disagreed on when to “arm the ground spoilers.”
I’m not a pilot, so the exact procedure for this manoever is not something I totally understand. But from what I was able to learn, arming the ground spoilers is executed just above the runway, causing the aircraft’s nose to rotate up. That ensures the nose wheel does not contact the runway first, and it also reduces the rate of descent so that the main wheels will not impact the runway too hard. The thrust of the engines is reduced at the same time, causing the speed of the aircraft to slow significantly.
They both agreed they did not like arming them at the beginning of the final approach, fearing it could lead to an inadvertent spoiler deployment. The captain preferred arming them on the ground, while the copilot preferred arming them during the landing flare.
So they compromised. When the captain was piloting the aircraft, the first officer would deploy the spoilers on the ground, as he preferred, and when the first officer was piloting the aircraft the captain would arm them on the flare as copilot preferred.
On July 5, there was a miscommunication. The pilot said, “All right. Give them to me on the flare,” and then said, “Okay.” The copilot immediately deployed the spoilers on the flare, instead of just arming them. The plane began to sink heavily, so the captain had to pull back on the control column and applied full thrust to all four engines. The copilot realized his mistake and apologized.
The nose lifted, but the aircraft continued to sink, hitting the runway with enough force that the number four engine and pylon broke off the wing. The captain managed to lift off for a go-around, but was unaware that the lost fourth engine had torn off a piece of the lower wing plating and the aircraft was now trailing fuel, which ignited. They requested from the tower to land on the same runway, but were told that there was too much debris and were given another runway.
Two and a half minutes after the initial collision, the right wing above engine number four exploded, causing parts of the wing to break off, and six seconds after this explosion, another explosion occurred in the area of the number three engine, causing the pylon and engine to both break off and fall to the ground in flames. Six and a half seconds after the second explosion. After that, a third explosion occurred, destroying most of the right wing, including the wing tip. The plane then went into a violent nose dive, striking the ground at a high velocity of about 220 knots (407 km/h) and killing all 100 passengers and the nine crew members on board.
The mishap was the first Air Canada accident involving fatalities since November 1963, when another DC-8, Flight 831 crashed with a loss of 118 lives.