Anchorage, Alaska. “On June 8, 2020, about 0945 Alaska daylight time, a float-equipped Piper PA-12 airplane, N3188M, sustained substantial damage when its rudder structurally failed in flight about 8 miles north of Anchorage, Alaska.2 The flight instructor and private pilot receiving instruction were not injured.
While on a left crosswind leg after takeoff from a lake, the airplane yawed abruptly to the right and the pilot indicated that the controls “felt strange.” The flight instructor assumed control of the airplane and noticed drastically diminished control about the vertical axis. In addition, significant downward elevator pressure (forward control yoke) was required. In an effort to aid in directional control, the water rudders were deployed. Uncertain that he could make a 180° turn due to the poor directional control, the flight instructor elected to return to the airport from which they had departed and landed without further incident”.

Anchorage, Alaska. “On July 23, 2021, about 1510 Alaska daylight time, a float-equipped Piper PA-14 airplane, N4206H, sustained substantial damage when its rudder structurally failed in flight about 15 miles southeast of Anchorage, Alaska.3 The commercial pilot was not injured.
The pilot reported that while in level cruise flight, frequent left and right rudder inputs were required to keep the inclinometer centered, similar to a light turbulence encounter.4 The airplane then began to experience a constant yaw, with elevator adjustments required to maintain level flight. He stated that the oscillation then stopped and a “a very large right rudder input” was required to maintain the course heading. He was able to land the airplane without further incident”.

Conclusions

“It is likely that each of the five recently examined Piper Aircraft Inc. part number 40622 rudder posts, all made of American Iron and Steel Institute 1025 carbon steel, fractured due to fatigue.
Posts made of American Iron and Steel Institute 1025 carbon steel in
Piper Aircraft Inc. part number 40622 rudders are susceptible to fatigue cracking under normal service conditions.
Recently documented structural failures of Piper Aircraft Inc. part number 40622 rudders equipped with a post made of American Iron and Steel Institute 1025 carbon steel indicate a serious hazard to flight safety that warrants action.”

New Recommendation

“Issue an airworthiness directive that describes the safety risk associated with the continued use of Piper Aircraft Inc. part number 40622 rudders equipped with a post made of American Iron and Steel Institute (AISI) 1025 carbon steel and that requires owners and operators to address the unsafe condition, such as by replacing them with rudders equipped with a post made of AISI 4130 low-alloy steel or its equivalent. (A-22-3)”

Source:
https://www.ntsb.gov/investigations/AccidentReports/Reports/AIR2202.pdf