Newark International Airport
Aircraft Accident/Incident Report

Newark, New Jersey 07114
Tuesady, April 25, 2000 19:42 EDT

At V1, the DC-10-30's number 1 engine, a General Electric CF6-50C2, experienced a casing breach when the 2nd-stage low pressure turbine (LPT) anti-rotation nozzle locks failed. The breach occurred in the turbine plane, between approximately the 3 o'clock and 9 o'clock positions. Debris from the breach resulted in collateral damage to the numbers 2 and 3 engines, the fuselage, and the left landing gear. In May 1993, the engine manufacturer issued a service bulletin to replace existing nozzle locks with ones that had thicker posts and arms. The change required modification of the LPT case nozzle lock holes. In March 1994, the manufacturer issued another service bulletin, SB 72-1082, which introduced a newly designed nozzle lock. The new locks, which were installed on the accident engine, utilized original diameter stud shanks, but were manufactured from a different material, and did not require modification of the LPT case. There were two previously reported failures of SB 72-1082 LPT nozzle locks, discovered during routine under-cowl inspections. In one case, all of the 2nd-stage nozzle locks were broken. The nozzle segments had rotated 120 degrees within the LPT case, but the case itself was not breached. In the second case, two 4th-stage nozzle locks had failed, but there was no collateral damage. According to the engine manufacturer, the failures were intergranular, "suggesting either stress rupture or sustained peak low cycle fatigue." Safety Board examination, of the only two recovered 2nd-stage nozzle locks from the accident engine, along with a section of casing with a nozzle lock stud attached, revealed intergranular fracture features, degradation at the surface of the fracture features, and grain boundaries, typical of oxidation damage. The intergranular fractures and oxidation damage found at the grain boundaries were consistent with stress rupture. An examination of a cracked 2nd stage nozzle lock, from a comparison engine, also revealed oxidation and intergranular fracture features, consistent with stress rupture.

Stress rupture of the 2nd-stage low pressure turbine anti-rotation nozzle locks, resulting from inadequate nozzle lock design.