BOEING 757DELTA AIR LINES INC
Las Vegas, NV, USA · 2008-08-06·N666DN
What happened
NTSB summary, verbatimThe 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.
Photographs
63the aircraft, and what the investigators foundPhotographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.
Probable cause
the Board's determinationThe 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.
Occurrence sequence
1 stepsNTSB coding · CICTT taxonomy- 1 · Takeoff-rejected takeoffPowerplant sys/comp malf/faildefining event
Findings
1 causal · 0 contributing- CAUSEAircraft › Aircraft power plant › Engine (turbine/turboprop) › Turbine section — Failure
Safety recommendations
2 issuedwhat changed because of this accidentTO THE FEDERAL AVIATION ADMINISTRATION: Require that Pratt & Whitney PW2037 engines be removed from service for inspection of the 2nd stage turbine hubs when they have accumulated significantly fewer hours and/or cycles than the incident engine (10,880 hours and/or 4,392 cycles). (Urgent)
TO THE FEDERAL AVIATION ADMINISTRATION: Require that Pratt & Whitney PW2037 2nd stage turbine hubs undergo recurring inspections when they have accumulated significantly fewer hours and/or cycles than the incident engine (10,880 hours and/or 4,392 cycles) until the cause for the previous instances of cracking is identified and corrective action to prevent future cracking is implemented. (Urgent)
Sequence of events
7 timed eventsfrom the FDR factual report · claude-sonnet-5- 15:45 PDTTakeoffp.1Delta Airlines 624, a Boeing 757-232 equipped with Pratt & Whitney PW2037 engines, experienced an uncontained failure in the turbine area of the No. 2 (right) engine
- N/ATakeoffp.1The crew received a No. 2 engine fire warning light and rejected the takeoff
- N/ARejected takeoffp.1Smoke was observed from the No. 2 engine at the time the takeoff was rejected
- N/APost-eventp.1Metal debris was found on the runway after the airplane had taxied clear
- N/APost-eventp.1Examination of the engine at the gate revealed a hole in the engine cowl that was in line with a hole in the high pressure turbine case
- SRN 91454Takeoffp.4The Eng2 Vib parameter shows a rise in engine vibration
- SRN 91462Takeoffp.4The Eng2 Fire indication is set
NTSB analysis
from the final reportThe 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.