History of the Flight
On September 18, 2014, at approximately 0930 Pacific standard time, a jetBlue Airways Airbus A320-232, registration N656JB, flight number 1416, departed Long Beach Airport (LGB) for Austin-Bergstrom International Airport. During initial climb, while passing through about 10,000 feet above ground level, the flightcrew received multiple Electronic Centralized Aircraft Monitor (ECAM) messages including an "ENG 2 FIRE WARNING" and noted smoke in the cabin. The crew shut down the No. 2 (right) engine, discharged both fire extinguishing bottles, and initiated an air turnback to Long Beach. The airplane landed uneventfully on the remaining engine, and Airport Rescue and Firefighting personnel observed no external damage. Of the 142 passengers and 5 crewmembers, none reported injuries. Day visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed.
Engine Damage Examination
Post-flight inspection of the airplane revealed heat distress and delamination in the No. 2 engine thrust reverser, small impact marks (without skin penetration) on the right aft fuselage near the rear cargo door and right horizontal stabilizer. Examination of the engine showed considerable low pressure turbine (LPT) blade damage and a fractured fuel pressure line to the station 2.5 low pressure compressor bleed valve slave actuator.
The engine was removed and shipped to MTU in Germany for detailed examination. External inspection revealed thermal distress including consumed or partially consumed insulation blankets, loop clamp cushions, wiring harness sheathing, and sooting. No case breaches or penetrations were noted, though the LPT case exhibited a localized outward bulge. Disassembly showed that all high pressure turbine (HPT) stage 2 blades were present except two that had released with their roots. A single fir tree blade retaining lug from the HPT stage 2 disk had fractured between the inner and middle attachment teeth, releasing two HPT stage 2 blades. Upstream turbine hardware was undamaged, while remaining HPT stage 2 blades and downstream hardware showed heavy secondary impact damage, tears, and material loss.
Test and Research
Metallurgical examination of the fractured HPT stage 2 disk lug by IAE revealed fatigue from multiple origins propagating from the pressure side (PS) of the middle (No. 2) fillet toward the suction side, eventually fracturing due to progressive tensile overload. A concave 'divot' measuring up to 0.0008 inches deep was found in the PS No. 2 fillet adjacent to the fracture surface, running the entire fillet length. Similar 'divots' were observed on all remaining lugs, leading IAE to conclude the groove was a tool mark from the original broaching operation. Shadowgraph inspection showed the tool mark created an irregular profile. Bulk microstructure was typical of properly processed IN-100 powder metal.
Additional Information
IAE examined HPT stage 2 disks broached before (disk 7.1) and after (disk 7.2, the failed disk) the same broaching tool cycle. Disk 7.1 had tool marks in the last 20 of 72 blade slots; disk 7.3 (next sequential disk) had tool marks in all 72 slots. A subsequent disk (8.1) broached after tool reconditioning also showed tool marks in all 72 slots, including an additional unique tool mark on the PS No. 3 fillet. Reconditioning did not eliminate the 'divot'.
An audit team from IAE, Avio Aero (the machinist), and General Electric identified primary contributing factors: cutter tool draft angle design causing scuffing and rapid wear, non-optimized tool redressing, and procedural issues with inspection. Best practices from GE and IAE were implemented. IAE proposed a fleet management plan including a Non-Modification Service Bulletin for once-through inspection of all Avio-manufactured HPT stage 1 and 2 disks. The FAA indicated they would issue an Airworthiness Directive mandating inspections.