The No. 1 (left) engine high pressure turbine (HPT) stage 1 aft blade retainer developed a fatigue crack that initiated and propagated through thickness and circumferentially until final overload failure that was not contained by the turbine case. Fractography of the HPT stage 1 aft blade retainer revealed the crack initiated in the upper collet radius at a single point of origin which corresponded to a surface connected material anomaly that measured 0.005 inches by 0.015 inches by 0.0005 inches. The fracture surface contained an area of intergranular fracture morphology with visible beach marks, consistent with hold-time fatigue growth and the remaining fracture surface was consistent with overload fracture. Further examination of the material anomaly was determined to be a cluster of particles enriched with Titanium, Aluminum, Zirconium, Magnesium, and Oxygen, which is consistent with Oxide/Carbonitride/Nitride/Carbide (OCNC) particles. Analysis of the HPT stage 1 aft blade retainer material found all dimensional and material characteristics to be conforming to GE Aerospace drawings and material specifications. The presence of OCNC particles and clusters of particles is inherent to Rene 65 material with quantity and size distributions accounted for within GE’s philosophy for material life limit calculations. The calculated stress conditions for the GEnx HPT stage 1 aft blade retainer collet feature were found to be uniquely high when compared to the stress conditions of other rotating hardware. This higher stress environment was determined to be the result of the assembly interference fits between the HPT stage 1 disk, the HPT stage 1 aft blade retainer, and the HPT mid seal in combination with the engine’s operational loads. Analysis of material test data suggests that surface connected OCNCs have a reduced crack incubation/nucleation life at high stress conditions, and that surface connected OCNCs do not behave according to traditional crack growth threshold behavior. Activation of surface connected OCNCs can in fact reduce material fatigue life capability but not every OCNC will initiate a crack, suggesting an unknown bimodal behavior.
The uncontained left engine failure was caused by the failure and liberation of the HPT stage 1 aft blade retainer as a result of a fatigue crack in the upper collet radius that originated from a surface connected cluster of Oxide/Carbonitride/Nitride/Carbide (OCNC) particles. Contributing to the failure of the HPT stage 1 aft blade retainer was an unknown material behavior unique to OCNC clusters in Rene 65 material that are surface connected in highly stressed material that may result in a localized reduction of material fatigue life capability.
Boeing 787-9 · N27957 — 63,592 samples, 20 parameters, 13:09:41.0 to 15:22:09.9.
| Time | Event | Page |
|---|---|---|
| 1336 UTC | Aircraft departed Singapore and climbed uneventfully to 31,000 ft (FL310) | 5 |
| 1408:48 UTC | With the aircraft stable at FL310 and 312 kts computed airspeed, engine 1 (the left engine) N1, N2, and fuel flow all abruptly decreased | 5 |
| 1408:55 UTC | The left engine fire warning became active | 5 |
| 1409:24 UTC | The engine 1 fuel cutoff switch was moved from the run position to the cutoff position | 5 |
| 1409:28 UTC | The engine 1 fire switch was pulled | 5 |
| 1409:40 UTC | The left engine fire bottle was discharged | 5 |
| 1409:55 UTC | The left engine fire warning cleared | 5 |
| 1504 UTC | The aircraft returned to Singapore and made an uneventful single-engine landing | 5 |
| Group | Title | Pages | Type |
|---|---|---|---|
| fdr | FDR-RECORDERS REPORT_ENG24LA014_FINAL | 14 | |
| fdr | FLIGHT DATA RECORDER FACTUAL REPORT - ATTACHMENT 1 | 1 | csv |
Docket: data.ntsb.gov/Docket/?NTSBNumber=ENG24LA014. This brief is an analytical aid assembled from public records; it is not an investigative finding.