Boeing 787 N27957

Summary

On 14 May 2024 at about 14:00 local time, a Boeing 787 registered N27957, operated by United Airlines, was involved in an incident near Singapore, Singapore. 210 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

14 May 2024 at 14:00

Classification

Incident

Location

Singapore, Singapore

Coordinates

2.0379, 107.0497

Aircraft

Boeing 787

Registration

N27957

Category

Airplane

Engines

2

Operator

United Airlines

Operating rule

Part 121: Air Carrier

Phase of flight

Not recorded

Route

Singapore → San Francisco

Aircraft damage

Minor

Weather

VMC

Light

Night

NTSB number

ENG24LA014

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.