Airbus A220 HB-JCA

Summary

On 16 September 2019 at about 19:25 local time, a Airbus A220 registered HB-JCA, operated by Swiss International Air Lines, was involved in an incident near Côte-d'Or Region, France. 77 people were on board and nobody was injured. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

16 September 2019 at 19:25

Classification

Incident

Location

Côte-d'Or Region, France

Coordinates

47.9781, 5.0182

Aircraft

Airbus A220

Registration

HB-JCA

Category

Airplane

Year built

2017

Engines

2

Operator

Swiss International Air Lines

Operating rule

Non-U.S., Commercial

Phase of flight

Not recorded

Route

Geneva → London

Aircraft damage

Not recorded

Weather

Unk

Light

Night

NTSB number

ENG19IA034

Nobody was injured.

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 because 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.

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

Read the full NTSB narrative

The No. 1 engine low pressure compressor (LPC) stage 1 integrally bladed rotor (IBR) failure was caused by a stage 1 IBR high cycle fatigue crack that originated at the runout of an airfoil leading edge root radius. Multiple analytical methods, including two-dimensional (2D) computational fluid dynamics (CFD), acoustic testing, and instrumented flight testing identified a coupled LPC stage 3 and stage 1 IBR instability caused by an acoustic coincidence with the 2.5 bleed valve duct cavity. At high engine N1 speeds, the stage 3 IBR blade tips generate vortices/turbulent airflow and given the right conditions, the turbulent airflow can create an acoustic tone as it passes over the 2.5 bleed valve duct cavity, located immediately aft of the LPC stage 3 IBR (Figure 1). The acoustic tone drove a LPC stage 3 IBR blade 1st bending mode excitation that was then mechanically transferred through the LPC module and excited a LPC stage 1 IBR stiffwise bending mode that was present at the same approximate frequency. The resultant stresses on the LPC stage 1 IBR blades exceeded material limits and subsequently led to crack formation and eventual progression to overload failure. Figure 1- Engine LPC Diagram Identifying the IBR 3 / 2.5 Bleed Valve Acoustic Interaction Factors that contributed to the LPC stage 3 and stage 1 IBR acoustic coincidence and blade excitation within the engine operating range were: installation of electronic engine control (EEC) Software V2.11.7.2 and the low time rub in period on the LPC IBR blade tip clearances. EEC Software V2.11.7.2 changed the LPC inlet guide vane schedule to rotate the IGV’s in the closed direction at specific high power engine conditions to improve engine stall/surge margin. The revised vane schedule inadvertently created conditions that were favorable for generation of the 2.5 bleed valve duct cavity acoustic tone and IBR mode excitation. New engines have tighter clearances between the LPC IBR blade tips and the outer air seals. The reduced clearance created unsteady loading at the blade tip region and resulted in stronger acoustic coupling/flutter response. After a rub in period, the clearance increases, and the occurrence of flutter onset is reduced. This incident was the second of four Airbus A220-300 PW1500G LPC stage 1 IBR separations that occurred between July 25, 2019 and February 12, 2020. The findings from the first LPC stage 1 IBR failure investigation are available in the NTSB investigation number ENG19IA029 docket.

Quoted verbatim from the NTSB record.