What happened
On 14 September 2008, a Zenair CH601 micro light aircraft, registration PH-4B6, was conducting a recreational flight over the Netherlands. The aircraft departed from Middenmeer airfield carrying a pilot and one passenger. After performing several turns near Medemblik, the aircraft proceeded south toward Hoorn.
While cruising at an altitude of approximately 1100 feet over the Markermeer, the aircraft's right-hand wing suddenly buckled upward. This structural failure caused the aircraft to enter a steep dive, rotating around its longitudinal axis, before impacting the water. Both occupants were fatal in the crash, and the aircraft was destroyed.
The investigation
The Dutch Safety Board conducted a technical investigation involving experts in aircraft structures and materials, alongside the National Aerospace Laboratory. Investigators recovered the wreckage from approximately three meters below the water surface.
Analysis of the wreckage revealed significant damage to the right-hand wing, including a twisted and broken main spar and a failed wing box assembly. The investigation also examined the aircraft's flight path using GPS data, which confirmed the aircraft was flying within its prescribed speed limits at the time of the accident. Furthermore, investigators reviewed a history of similar wing-collapse accidents involving the Zenair CH601 model in several other countries.
Findings
Technical examination of the PH-4B6 identified that the right-hand wing main spar had buckled near the fuselage. The investigation established that the rivet joints between the main spar and the wing skin had failed over a distance of more than one meter. Additionally, the rear attachment assembly connecting the right wing to the fuselage had failed, and the aileron control system showed signs of heavy overloading and extreme deflection.
Safety action
Following the publication of a preliminary report regarding this accident and other similar occurrences, the Dutch Inspectorate for Transport and Water Management imposed a flying ban on all Zenair CH601XL aircraft registered in the Netherlands. This ban was subsequently adopted by aviation authorities in several other nations to prevent further occurrences of similar structural failures.