Poor maintenance results in accident

Aircraft: Great Lakes 2T-1A-2. Injuries: None. Location: Kingsville, Texas. Aircraft damage: Substantial.

What reportedly happened: The purpose of the flight was to give the pilot a chance to practice aerobatic maneuvers for an upcoming airshow. After completing a hammerhead turn, he felt a slight vibration and the pitch control felt unusual. Returning to the airport, the vibration increased. The pilot landed but was unable to maintain directional control and the airplane ground-looped.

The post-landing inspection revealed the right horizontal stabilizer and elevator had separated from the airplane, striking the rudder and causing substantial damage. Closer examination revealed evidence of a pre-existing crack in the front spar near a riveted fitting. The spar moved outward and disengaged from the fitting. The inboard section rotated downward and separated from the airplane. The remaining portion of the stabilizer pivoted aft, separated from the airplane, and struck and damaged the rudder.

A service alert from the airplane’s manufacturer outlined a similar previous occurrence. Another emphasized the importance of properly rigged tail wires, noting that if the tail wires were improperly rigged, excessive torque loads could be applied to the horizontal stabilizer front spar, causing the attach fitting to fail. Examination of the last annual inspection entry disclosed no reference to the horizontal stabilizer spar being inspected, nor did it indicate that either service bulletin had been complied with.

Probable cause: A pre-existing crack in the front spar of the right horizontal stabilizer near a riveted fitting, causing it to fail and separate from the airplane in flight. Contributing to the accident was the failure of maintenance personnel to comply with existing service bulletins and to detect and repair the damaged spar.

NTSB Identification: CEN11LA209

This February 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.