Airbus A220 HB-JCM

Summary

On 25 July 2019 at about 11:05 local time, a Airbus A220 registered HB-JCM, operated by Swiss International Air Lines, was involved in an incident near Perrigny-sur-Armançon, France. 121 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

25 July 2019 at 11:05

Classification

Incident

Location

Perrigny-sur-Armançon, France

Nearest airport

Charles de Gaulle (CDG)

Coordinates

47.6900, 4.2387

Aircraft

Airbus A220

Registration

HB-JCM

Category

Airplane

Year built

2018

Engines

2

Operator

Swiss International Air Lines

Operating rule

Non-U.S., Commercial

Phase of flight

Not recorded

Route

Geneva → London

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

ENG19IA029

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 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.

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

Read the full NTSB narrative

The No. 1 (left) engine low pressure compressor (LPC) stage 1 integrally bladed rotor (IBR) separation was caused by a high cycle fatigue (HCF) crack that originated at the runout of an airfoil leading edge root radius. Acoustic tests, instrumented flight tests, and multiple analytical methods were completed and identified a mechanically coupled LPC stage 3 and stage 1 IBR mode excitation driven by an acoustic coincidence with the 2.5 bleed valve duct cavity. At high engine speeds in specific flight conditions, unsteady or turbulent airflow generated by the LPC IBR blade tips created an acoustic tone as it passed over the 2.5 bleed valve duct cavity, located immediately aft of the LPC (Figure 1). The acoustic tone excited a LPC stage 3 IBR blade 1st bending mode that was mechanically transferred through the LPC module to the LPC stage 1 IBR where a stiffwise bending mode was excited. 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 stage 3 IBR / 2.5 Bleed Valve Acoustic Interaction Factors that contributed to the LPC acoustic coincidence within the engine operating range were installation of electronic engine control (EEC) Software V2.11.7.2 and low engine operating hours. EEC Software V2.11.7.2 modified the LPC inlet guide vane (IGV) schedule to improve engine surge/stall margin in high power flight phases such as top of climb, by rotating the vanes in the closed direction. The revised vane schedule inadvertently created conditions that were favorable for LPC IBR 3 and IBR 1 flutter onset.   New engines have tighter clearances between the LPC IBR blade tips and the outer air seals. The tighter clearances created unsteady loading at the blade tip region and resulted in stronger acoustic coupling and flutter response. Flight test data confirmed that acoustic coincidence and flutter response within the engine operating range was significantly reduced following an engine rub in period. The Powerplant Group Chairman’s Factual Report available in the investigation docket includes additional information on the LPC acoustic coincidence and the testing and analytical methods used to identify the failure mode.

Quoted verbatim from the NTSB record.