What happened
Two significant aviation incidents involving the Boeing McDonnell Douglas DC-10 occurred at Amsterdam Airport Schiphol within a year of each other. On December 18, 1999, a DAS Air Cargo freighter, registration N800WR, experienced an uncontained failure of its tail engine during the takeoff roll. The failure caused engine components to be ejected from the engine casing, penetrating the engine cowling and striking the aircraft's elevator. This resulted in substantial damage to the engine and the rear structure of the aircraft, forcing the crew to abort the takeoff.
On September 7, 2000, a second incident occurred involving a Continental Airlines Boeing McDonnell Douglas DC-10-30, registration N15069. During its takeoff roll at Schiphol, the left engine suffered an uncontained failure where low-pressure turbine components were ejected through the engine nacelle. Unlike the previous event, this failure did not cause damage to the aircraft fuselage or wing fuel tanks.
The investigation
The investigation examined the mechanical failures of both engines to determine the root causes of the component ejections. For the DAS Air Cargo incident, investigators focused on the engine's inlet assembly. For the Continental Airlines event, the investigation looked into the structural integrity of the low-pressure turbine components and the possibility of fatigue-related failures.
Findings
In the case of the DAS Air Cargo N800WR, the investigation concluded that a faulty installation of a mounting bracket for the bellmouth assembly was the most likely cause. It is believed that this bracket failed, allowing the bellmouth assembly—a component of the engine inlet located between the engine and the airframe—to be ingested into the engine.
Regarding the Continental Airlines N15069, the investigation established that the failure was caused by the fatigue-induced breakage of turbine nozzle locks. The investigation found that the design of these locks did not sufficiently account for the thermal and time-dependent stresses experienced during operation. Specifically, the locks failed due to intercrystalline cracking caused by creep and fatigue loading, which led to the rotation and subsequent ejection of the turbine vane segments.
Safety action
Following the Continental Airlines incident, a safety recommendation was issued to the engine manufacturer, General Electric, to develop an improved nozzle lock design for the CF6-50 engines. The manufacturer subsequently implemented a new design featuring thicker components and a doubled number of locks in the second turbine stage. Since these design improvements and the implementation of updated maintenance procedures, no further incidents of this specific nature have been reported.