What happened
On March 8, 2017, a Burkhart Grob G 109B powered glider, registration N109FH, was performing a turn in cruise flight when the pilot experienced unusual movement in the rudder pedals. Upon inspecting the rear of the aircraft, the pilot observed that the rudder had detached from the top of the vertical stabilizer. The pilot noted that the resulting adverse yaw was mild and proceeded to land the aircraft. During the landing roll, the rudder further separated from the empennage. There were no injuries resulting from the event.
The investigation
FAA photographs of the rudder hinges revealed extensive corrosion. The upper hinge exhibited a clean fracture surface on both the rudder and the vertical stabilizer sides. The aircraft was parked in an outdoor tie-down space at an airport located less than one-half mile from the Pacific Ocean.
Maintenance records indicated that the most recent annual inspection had been completed approximately 14 months prior to the accident. A 6,000-hour "Extension of Life Time" inspection had been performed roughly nine months before the accident. While most items on the 6,000-hour inspection checklist were initialed as satisfactory, the line items for visual checks for decay regarding the aileron, fuselage controls, elevator/trim tab, and rudder were left uninitialed.
The mechanic responsible for the recent inspections stated that no abnormalities were noted and that the decay checks were performed and found satisfactory, despite the lack of initials on the checklist. The mechanic suggested that corrosion could develop rapidly in such a marine environment and recommended more frequent inspections and daily rinsing with water to remove salt residue.
Findings
- The aircraft was operated in a marine environment subject to ocean spray.
- The upper rudder hinge failed due to severe corrosion.
- The most recent annual inspection was overdue by approximately two months.
- The pilot believed the 6,000-hour inspection had renewed the annual inspection requirement, but later learned the annual inspection had not been performed.