Boeing 757 N666DN incident near Las Vegas, Nevada

Probable cause

The engine experienced an uncontained release of high pressure turbine material due to fatigue cracks that occurred on four consecutive blade retainig lugs on the 2nd stage turbine hub. The cracked lugs resulted in the release of four 2nd stage turbine blades that penetrated the engine's cases and nacelle. The lugs cracked due to loss of material and resultant increase in stress load on the blade slot serrations due to excessve grit blasting when the hub was being overhauled by Delta Air Lines. Contributing to the uncontained incident was the FAA's and Pratt & Whitney's failure to act in a timely manner when another PW2037 2nd stage turbine hub was found to have multiple cracks in the blade retaining lugs.

NTSB analysis

The Delta Air Lines Boeing 757 airplane had just started its takeoff roll from the McCarran International Airport, Las Vegas, Nevada, when the right engine, a Pratt & Whitney (P&W) PW2037, experienced an uncontained release of high pressure turbine material. The examination of the engine revealed a hole in the high pressure and low pressure turbine case flanges at the bottom of the engine in line with the 2nd stage turbine rotor. The engine was removed from the airplane and shipped to Delta's Technical Operations Center for disassembly. The disassembly revealed four adjacent 2nd stage turbine blades were missing. In addition, the 2nd stage turbine hub had four blade retaining lugs that were fractured. Metallurgical examination of the fractures determined the fractures were due to fatigue at elevated temperatures from multiple origins along the blade slot serrations. The metallurgical examination also revealed that there were no material defects in the hub. A dimensional inspection of the hub's blades slots showed that they were missing material. Delta reported that they had to use a grit blasting procedure that was more agressive to remove the varnish-like scale from the hub in order to clean it sufficiently to permit the fluorescent penetrant inspection. Although the incident hub was only grit blasted one time, maintenance records for another PW2037 2nd stage hub that was found to have multiple cracks in the blade slots showed that it had been grit blasted multiple times to clean the hub. Grit blasting tests conducted by P&W showed that if the appropriate grit blasting procedures were not adhered to that significant material loss could result.

Text from the NTSB. Open the NTSB docket for ENG08IA038 for the full record.