What is the longest period of time an aircraft type has been grounded due to safety concerns? Obviously inspired by the current 737 Max situation, what is the longest period of time that any individual type of airliner has been grounded for safety concerns (excluding those that never returned to service)?
The Yak-42 was grounded from June 1982 to October 1984 (26 months) for a cause similar to Alaska Airlines Flight 261.