Swiss BCS3 near Paris on Jul 25th 2019, engine shut down in flight
Last Update: March 4, 2021 / 21:58:59 GMT/Zulu time
Incident Facts
Date of incident
Jul 25, 2019
Classification
Incident
Airline
Swiss
Flight number
LX-348
Departure
Geneva, Switzerland
Destination
London Heathrow, United Kingdom
Aircraft Registration
HB-JCM
Aircraft Type
Airbus A220-300
ICAO Type Designator
BCS3
A passenger reported the engine emitted a loud bang and streaks of flames, the crew diverted to Paris for a safe landing.
On Aug 9th 2019 the French BEA reported the left hand engine failed while the aircraft climbed through FL320 and was shut down. The aircraft diverted to Paris CDG Airport. A post flight examination revealed the low pressure compressor rotor stage 1 was missing from the engine. There were no injuries, the aircraft sustained minor damage. The BEA delegated and the NTSB accepted the delegation of the investigation. The occurrence was rated a serious incident and is being investigated by the NTSB.
On Aug 20th 2019 the BEA, on behalf of the NTSB, published a call for witnesses stating:
On behalf of the NTSB, the BEA is issuing a call for witnesses regarding engine parts that may have fallen in an unoccupied wooded area near the towns of Perrigny-sur-Armancon and Cry. The four points of the search zones are at the following GPS coordinates:
47°41'40"N 4°14'16"E / 47°42'04"N 4°14'52"E / 47°40'30"N 4°16'14"E / 47°40'20"N 4°15'57"E
providing a map (see below).
The FAA released an Air Worthiness Directive 2019-19-11 requiring following actions on Pratt & Whitney Models PW1519G, PW1521G, PW1521GA, PW1524G, PW1525G, PW1521G-3, PW1524G-3, PW1525G-3, PW1919G, PW1921G, PW1922G, PW1923G, and PW1923G-A turbofan engines that have accumulated fewer than 300 flight cycles:
(1) Within 50 flight cycles from the effective date of this AD, and thereafter at intervals not to exceed 50 flight cycles until the engine accumulates 300 flight cycles, borescope inspect each LPC inlet guide vane (IGV) stem for proper alignment.
(2) Within 50 flight cycles from the effective date of this AD, and thereafter at intervals not to exceed 50 flight cycles until the engine accumulates 300 flight cycles, borescope inspect the LPC R1 for damage and cracks at the following locations:
(i) The blades tips;
(ii) the leading edge;
(iii) the leading edge fillet to rotor platform radius; and
(iv) the airfoil convex side root fillet to rotor platform radius.
(3) As the result of the inspections required by paragraphs (g)(1) and (2) of this AD, before further flight, remove and replace the LPC if:
(i) An IGV is misaligned; or
(ii) there is damage on an LPC R1 that exceeds serviceable limits; or
(iii) there is any crack in the LPC R1.
The FAA argued the AD is necessary:
The FAA received reports of two recent IFSDs on PW PW1524G-3 model turbofan engines. The first IFSD occurred on July 25, 2019 and the second IFSD occurred on September 16, 2019. These IFSDs were due to failure of the LPC R1, which resulted in the LPC R1 releasing from the LPC case and damaging the engine. LPC rotor failures historically have released high-energy debris that has resulted in damage to engines and airplanes (see Advisory Circular (AC) 39-8, “Continued Airworthiness Assessments of Powerplant and Auxiliary Power Unit Installations of Transport Category Airplanes,” dated September 8, 2003, available at rgl.faa.gov). Although these IFSDs occurred on PW PW1524G-3 model turbofan engines, the FAA is including PW PW1900 engines in the applicability of the AD because similarities in type design make these engines susceptible to the same unsafe condition as PW PW1500 engines. This condition, if not addressed, could result in uncontained release of the LPC R1, in-flight shutdown, damage to the engine, damage to the airplane, and loss of control of the airplane. The FAA is issuing this AD to address the unsafe condition on these products.
According to this FAA AD the root causes of this and a later occurrence, see Incident: Swiss BCS3 near Geneva on Sep 16th 2019, uncontained engine failure are related.
On Oct 15th 2019 the BEA reported the two occurrences of Jul 25th 2019 and Sep 16th 2019 are "identical". So far, no parts of the engine of HB-JCM have been recovered. The NTSB asked for assistance to locate the parts, in particular a piece of titanium of about 70cm in diameter (possibly browk into smaller pieces). The BEA have therefore decided to set up a sweep of the search area and are looking for up to 150 volunteers to sweep the area on Nov 6th 2019 and Nov 8th 2019.
On Oct 26th 2019 Transport Canada issued an Emergency Airworthiness Directive (EAD) CF-2019-37 (subsequently also distributed by Switzerland's BAZL) stating:
Several occurrences of engine in-flight shutdowns (IFSDs) were reported on Airbus Canada Limited Partnership BD-500 family aeroplanes. Investigations are ongoing to determine the root cause. Preliminary investigation results indicate high altitude climbs at higher thrust settings for engines with certain thrust ratings may be a contributor. This condition, if not corrected, could lead to an uncontained failure of the engine and damage to the aeroplane.
To address this potentially unsafe condition, this AD introduces a new Aircraft Flight Manual (AFM) limitation and normal procedure to limit the engine N1 setting to 94% while above 29000 feet.
In the EAD required amendment to the Aircraft Flight Manual it is stated: "Caution: Before initiation of step climbs above 29000 feet, the autothrottle must be selected off to respect the 94% N1 limitation."
On Nov 6th 2019 the BEA reported a targeted search with the assistance by volunteers brought about 3 pieces of engine debris on the first day of the search (see photo below).
On Mar 31st 2020 the FAA released another Airworthiness Directive AD-2020-07-02 arguing:
The FAA has received reports of four instances of IFSDs occurring on the affected model turbofan engines since 2019.
In response to the two IFSDs that occurred in July and September 2019, and in response to ongoing investigations of these IFSDs, the FAA issued AD 2019-19-11 (84 FR 50719, September 26, 2019), to perform inspections of the LPC R1 to prevent failures. The FAA subsequently superseded AD 2019-19-11, issuing AD 2019-21-11 (84 FR 57813, October 29, 2019) in response to another IFSD and to expand the population of affected engines that needed inspection of the LPC R1. Since the effective date of AD 2019-21-11, another IFSD occurred in February 2020. Analysis by the manufacturer determined that the LPC vane schedules were putting the engine in a condition to experience an acoustic resonance that damages the LPC R1, which then leads to LPC R1 failure. In response, the manufacturer updated the EEC FADEC software to improve vane scheduling to avoid acoustic resonance.
This condition, if not addressed, could result in uncontained release of the LPC R1, damage to the engine, and damage to the airplane. The FAA is issuing this AD to address the unsafe condition on these products.
The four mentioned occurences are: Incident: Swiss BCS3 near Paris on Jul 25th 2019, engine shut down in flight, Incident: Swiss BCS3 near Geneva on Sep 16th 2019, uncontained engine failure, Incident: Swiss BCS3 near Paris on Oct 15th 2019, engine shut down in flight and Incident: Baltic BCS3 near Bordeaux on Feb 12th 2020, uncontained engine failure.
On Feb 9th 2021 the NTSB opened their investigation docket and released their factual report stating the aircraft "experienced a No. 1 engine failure while climbing through flight level 320 over Perrigny-sur-Armançon, France. The flight crew followed quick reference handbook procedures and attempted to shutdown the No. 1 engine, but the engine had already been shutdown by the EEC. The crew diverted to Charles de Gaulle International Airport (CDG), Paris, France and made an uneventful single engine landing. A post flight examination of the engine revealed a hole in the LPC case and the LPC stage 1 IBR (low pressure compressor stage 1 integrally bladed rotor) had separated and was missing. There were no passenger or crew injuries reported."
The NTSB described the damage:
The separated LPC stage 1 IBR penetrated the forward and mid LPC cases and created a hole from the 9 to 1 o’clock positions radially and between the forward flange of the forward LPC case and the aft flange of the mid LPC case axially. The separated LPC stage 1 IBR was contained by the nacelle and travelled aft through the bypass duct and was liberated out the back of the engine. The remaining LPC stages sustained secondary impact damage. Uncontained engine fragments also caused secondary impact damage to the trailing edge of all the fan blades and the trailing edge of eight consecutive fan exit guide vanes (FEGV) between the 10 o’clock and 11:30 positions. Thermal damage and material loss was observed in stages 5 through 8 of the high pressure compressor (HPC) and stage 2 of the high pressure turbine (HPT) during a borescope inspection (BSI) of the engine core. The low pressure turbine (LPT) stage 2 and 3 rotor blades were all broken, and the fracture surfaces were thermally distressed. The LPT stage 2 and 3 stator vanes exhibited coincident 360 degree impact damage.
Metallurgy
Multiple loose engine fragments, including a section of the separated LPC stage 1 IBR, were recovered from the nacelle and were shipped to the P&W Materials and Processes Engineering (MPE) Laboratory in East Hartford, Connecticut for examination. The fracture surface features on all recovered fragments were consistent with tensile-shear overload and a primary fracture surface was not identified.
...
Corrective Actions
Several corrective actions were released by P&W, Federal Aviation Administration (FAA), Airbus Canada, and Transport Canada to reduce the likelihood of additional events. A recurrent BSI inspection of the LPC stage 1 IBR was mandated and the inspections identified two additional LPC stage 1 IBR crack findings in the fleet. In addition to the recurrent BSI, an N1 speed restriction above FL290 was implemented to reduce the likelihood of mode excitation and an EEC software update, V2.11.9, was released to revert the LPC vane schedule back to the original vane schedule that was installed prior to the LPC stage 1 IBR failures. Finally, redesign efforts are underway to modify the 2.5 bleed valve duct geometry to increase the frequency margin and eliminate the resonant response within the engine operating range. According to P&W, redesigned hardware is scheduled to be available to the fleet by the fourth quarter of 2021.
On Mar 4th 2021 the NTSB released their final report concluding the probable causes of the incident were:
A No. 1 (left) engine low pressure compressor (LPC) stage 1 integrally bladed rotor (IBR) separation due to a high cycle fatigue crack (HCF) that originated at the runout of an airfoil leading edge root radius. The HCF crack developed as a result of a mechanically coupled LPC stage 3 and stage 1 IBR mode excitation and blade flutter response. The excitation was driven by an acoustic tone generated by turbulent airflow passing over the 2.5 bleed valve duct cavity while the engine was operating at high speeds in specific flight conditions. A primary contributor to the failure mode was an electronic engine control (EEC) software update that changed the LPC vane schedule and increased the likelihood of LPC stage 1 IBR blade flutter onset within the engine operating range.
Aircraft Registration Data
Incident Facts
Date of incident
Jul 25, 2019
Classification
Incident
Airline
Swiss
Flight number
LX-348
Departure
Geneva, Switzerland
Destination
London Heathrow, United Kingdom
Aircraft Registration
HB-JCM
Aircraft Type
Airbus A220-300
ICAO Type Designator
BCS3
This article is published under license from Avherald.com. © of text by Avherald.com.
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