The Accident-Heavy Douglas DC-10
Having had 55 accidents with many fatalities to date, the DC-10 is one of the most poorly-manufactured jets to exist. Probably the biggest issue with it is that the cargo doors opened outward opposed to inward like regular planes.
Due to this flaw, an improperly closed door flew open in the middle of a flight in 1972, alerting the need for a redesign. Something similar happened in 1974, and then in 1979, an engine fell off the wing during take-off. Today, the carrier is much safer thanks to many redesigns.