On October 31, 1987, an Enstrom F-28A (registration N9583) was involved in an aviation accident near Lapeer, MI. No fatalities were reported. Investigators recorded the probable cause as: The right horizontal stabilizer attach tube failed from fatigue originating at a surface defect on its outer diameter caused by misaligned drilling at the right inboard attach hole. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise, a helicopter's right horizontal stabilizer attach tube failed and separated, contacting the tail rotor. This resulted in failure of the tail rotor drive shaft flex coupling and loss of tail rotor thrust. The pilot performed a successful autorotation. Examination revealed fatigue from a surface defect caused by misaligned drilling at the attach hole.
Incident Description
A helicopter was in cruise flight when the right side horizontal stabilizer attach tube failed and separated from the tail boom. The separated tube then contacted the tail rotor. This contact resulted in failure of the tail rotor drive shaft flex coupling at the tail rotor gear box. Consequently, there was a loss of tail rotor thrust. The pilot executed a successful autorotation, landing in an open field.
Examination Findings
Examination of the right horizontal stabilizer attach tube revealed that it had failed due to fatigue. The fatigue crack originated at the right inboard attach hole. The origin was a surface defect on the outer diameter of the tube. This surface defect was caused by misaligned drilling during the manufacturing process.
Probable cause
The right horizontal stabilizer attach tube failed from fatigue originating at a surface defect on its outer diameter caused by misaligned drilling at the right inboard attach hole.
What happened in the 31 Oct 1987 Enstrom F-28A accident near Lapeer, MI?
During cruise, a helicopter's right horizontal stabilizer attach tube failed and separated, contacting the tail rotor. This resulted in failure of the tail rotor drive shaft flex coupling and loss of tail rotor thrust. The pilot performed a successful autorotation. Examination revealed fatigue from a surface defect…
Were there any fatalities in the 31 Oct 1987 Enstrom F-28A accident?
No fatalities were recorded in this accident.
What aircraft was involved and where did it happen?
The accident on 31 Oct 1987 involved an Enstrom F-28A, registration N9583, at Lapeer, MI.
What was the probable cause of the accident?
The right horizontal stabilizer attach tube failed from fatigue originating at a surface defect on its outer diameter caused by misaligned drilling at the right inboard attach hole.
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