The 737 rudder PCU also had a defect in the 90s that caused a series of major incidents, although obviously that's been fixed since: https://en.wikipedia.org/w

The 737 rudder PCU also had a defect in the 90s that caused a series of major incidents, although obviously that's been fixed since: https://en.wikipedia.org/wiki/Boeing_737_rudder_issues https://en.wikipedia.org/wiki/Boeing_737_rudder_issues