What happened
On October 13, 2018, an A220-100, registered as HB-JBC, was operating a scheduled flight from Paris-Charles de Gaulle to Zurich. During the climb phase, specifically around flight level 200 within the Paris Flight Information Region, the flight crew received consecutive warnings indicating low oil quantity and low oil pressure in the left engine. In response to these alerts, the crew followed established procedures to shut down the affected engine. The aircraft continued its flight to Zurich without further complications. While the crew sustained light injuries, the 112 passengers remained uninjured.
The investigation
Investigators determined that the oil loss in the left engine was caused by a faulty O-ring seal located at the fuel oil cooler. The investigation examined the maintenance history and manufacturer communications regarding the engine components. It was noted that a previous service bulletin from Pratt & Whitney, issued in June 2018, had recommended replacing the fuel oil cooler with a part featuring an increased thread length and higher tightening torque. However, this modification was categorized with low urgency and had not yet been implemented on HB-JBC.
Findings
- The primary cause of the engine shutdown was an oil leak originating from a defective O-ring seal at the fuel oil cooler.
- The manufacturer's initial recommendation for a hardware upgrade was not yet applied to the aircraft at the time of the incident.
Safety action
Following the incident, the manufacturer issued a more urgent service bulletin in October 2018, requiring periodic inspections of the connection for aircraft that had not yet received the modification. Subsequent inspections of the Swiss International Air Lines fleet identified two additional affected fuel oil coolers, which were subsequently replaced. Further updates to the service bulletins eventually included the replacement of the oil line leading to the connection. The FAA and EASA later issued an Airworthiness Directive making these corrective measures mandatory.