American Airlines went against manufacturer recommendations and used their own maintenance procedure to save 200 man hours of labor per aircraft. This resulted in one engine of AA Flight 191 separating from the wing on takeoff and the deaths of 273 people.
In 1982 a British Airways 747 had all 4 of its engines…
In 1982 a British Airways 747 had all 4 of its engines flame out after flying through a cloud of volcanic ash over Indonesia. The crew managed to maneuver the powerless plane through the cloud, restart all 4 engines in mid-air, and then safely make an emergency landing in Jakarta.