What happened
On July 7, 2001, a PIPER PA-34-200T, registration EC-EQV, was performing a dual instruction flight departing from Tenerife Norte Airport. The aircraft was occupied by a student pilot, an instructor, and a second instructor.
During the takeoff roll on runway 30, as the aircraft reached approximately 65 knots, the instructor noticed the left wing began to dip. To maintain control, the instructor took the controls, shut down the left engine, and feathered the propeller to decelerate the aircraft. As the speed decreased, the aerodynamic effectiveness of the control surfaces diminished, and the pilot was unable to prevent the left wing from dropping and impacting the pavement. This impact caused the aircraft to yaw around the left wingtip, leading to a runway excursion where the aircraft came to a stop within the runway safety area.
All three occupants survived the incident without injury. The aircraft sustained damage to the left propeller, the left wing, and the left main landing gear, which broke into two pieces.
The investigation
Investigators conducted a detailed laboratory analysis of the fractured left main landing gear strut. Visual inspection revealed significant areas of paint loss and evidence of corrosion pitting across the surface. The paint application was found to be irregular and non-homogeneous. Notably, at the ribbed intersection of the two tubes forming the shock absorber body, the paint had been mechanically removed, leaving prominent marks from a sharp object. A deep indentation was also identified on the front face of the strut near the fracture surface.
Laboratory testing, including hardness, conductivity, chemical composition, and metallographic studies, confirmed that the material used in the manufacturing of the strut was appropriate and met all required strength standards. The analysis determined that the failure was a semi-brittle tear that originated at a specific point on the exterior surface. This fracture propagated rapidly through the material, eventually leading to the failure of the remaining tube section under a static bending overload.
Findings
- The primary cause of the failure was a semi-brittle tear initiated by a mechanical notch (indentation) present on the strut.
- This mechanical notch acted as a stress concentrator, significantly reducing the local strength of the component.
- The failure occurred during the takeoff roll under normal operating loads, as the notch induced localized stresses far exceeding normal levels.
- It remains undetermined whether the mechanical notch was present prior to the flight or if it was created during the takeoff roll itself.