History of Flight
On October 15, 2013, at about 1451 CDT, a Spirit Airlines (NKS) Airbus A319, registration N516NK, experienced a No. 1 (left) engine failure during climb out from Dallas-Fort Worth International Airport (DFW), Dallas, Texas. The airplane was equipped with two International Aero Engines (IAE) V2524-A5 turbofan engines. About ten minutes after takeoff, at flight level 190, the electronic centralized aircraft monitor (ECAM) displayed a No. 1 engine pressure ratio (EPR) mode fault, N2 over limit warning, and an exhaust gas temperature (EGT) over limit warning. The ECAM notifications coincided with heavy vibrations felt throughout the cockpit and cabin. The flight crew advanced both engines to the take-off/go around (TO/GA) power setting. About four minutes later, a No. 1 engine fire warning registered, and the crew shut down the No. 1 engine and discharged one fire suppression bottle. Smoke entered the cockpit, and the crew donned oxygen masks. The airplane returned to DFW and executed an uneventful single-engine landing. Aircraft Rescue and Fire Fighting personnel met the aircraft and determined the fire had been extinguished. The flight was operated under 14 Code of Federal Regulations Part 121 as a regularly scheduled flight from DFW to Atlanta Hartsfield International Airport.
Injuries
No injuries were reported to passengers or crew.
Damage to Airplane
Visual examination revealed minor impact damage on the aft engine fairing, left wing fairing (canoe), and the leading edge of the left horizontal stabilizer. The impacts did not penetrate the outer panel or affect underlying structure. The No. 1 engine low pressure turbine (LPT) 3rd and 4th stage disks, turbine exhaust case center body, and the No. 5 bearing housing were jettisoned. The LPT 5th stage disk separated from the 6th stage disk and hung on the LPT shaft. Extensive damage occurred to all remaining high pressure turbine (HPT) and LPT hardware. Large sections of the LPT and exhaust cases were breached and not recovered. Engine cowlings were in good condition without indications of radial uncontainment. The No. 1 engine pylon exhibited sooting and substantial metal splatter above the LPT plane of rotation. Airbus deemed the pylon structure beyond repair limits, and it was removed and replaced.
Test and Research
The engine was shipped to the Pratt & Whitney Columbus Engine Center. The LPT shaft exhibited bending and heavy circumferential scoring. The LPT 6th and 7th stage disks remained intact but had substantial impact damage. All LPT 6th stage blades were missing; all LPT 7th stage blades were fractured at the root. The HPT 2nd stage disk had three blades separated below the platform with blade attachments secure in hub slots, and two blades were missing completely. Remaining blades exhibited hard body impact damage on leading and trailing edge surfaces. Components from the LPT, HPT, and No. 4 bearing compartment were analyzed. Three HPT 2nd stage blades fractured below the platform exhibited stress corrosion cracking (SCC) originating in the internal blade J-channel cooling air cavity. Of the 67 intact blades, 41 had varying levels of SCC. Probe spectrometry identified elemental sulfur at the corrosion front of each cracked blade examined. Hardness testing on HPT disks indicated exposure to temperatures exceeding 1950°F (1066°C). Hardness values increased by stage aftward and were lowest along disk outer rims, increasing toward center bores. The No. 4 bearing compartment fracture surfaces showed overload without fatigue indications; no fire exposure or thermal distress.
Crew Response
At the time of the event, the airplane was climbing out from DFW, and the crew navigated between two thunderstorm cells. Initial indications were a heavy audible vibration and an ECAM EPR mode fault. The crew began EPR mode fault emergency procedures and realized autopilot and autothrust had disengaged. The captain manually flew the airplane and advanced both throttles to TO/GA. The NKS Crew Operating Manual (COM) does not instruct throttle advancement in applicable abnormal/emergency procedures. The captain did not recall advancing throttles but stated he wanted to position for better troubleshooting. Advancing the throttle on the No. 1 engine did not further increase N2 speed because the engine was N2-limited by the full authority digital engine control, but it continued to subject HPT and LPT components to excessive gas path temperatures and vibration levels. The COM procedures for EPR mode fault, EGT overlimit, and N2 overlimit were reviewed. Maximum N1 and N2 speeds requiring engine shutdown were not reached. The COM states that when EGT limit is exceeded, operation may continue until next landing, but maximum temperature and duration should be recorded; if unable to maintain limits, the engine should be shut down. During the event, ECAM displayed an EGT warning, but the actual temperature showed amber X's due to gas path temperature exceeding probe sensing capability. The high vibration procedure does not require engine shutdown.
Additional Information
The ECAM warning sequence was evaluated by Airbus. Initially, EPR mode fault appeared, then N2 over limit, then EGT over limit, with warnings alternating due to FADEC control. The EGT probes on the V2524-A5 are temperature-rated to 1238°F (670°C). Maximum certified EGT was 1328°F (720°C) for 5 minutes. Probes can function up to 1400°F (760°C). The engine electronic control receives EGT signals up to 1830°F (999°C); above that, cockpit indication shows amber X's. The source of sulfur detected in cracked blades could not be identified. All 44 cracked blades were last repaired at Turbine Overhaul Services in Singapore. Cleaning procedures were verified non-corrosive. Environmental sulfur introduction was considered; the airplane flew over continental US, but IAE reported sulfur accumulation increasingly common for all engines due to pollutants.
Corrective Actions
Following the event, IAE revised HPT 2nd stage blade inspection criteria to better detect internal cracks during repair/overhaul, using x-ray and borescope. IAE/P&W developed an aluminide coating for internal cavities of HPT 2nd stage blades to protect against corrosive deposits and began installing new blades on production V2500 SelectOne engines. A service bulletin to retrofit in-service engines with new blades was expected in the first quarter of 2015.