What happened
On a scheduled flight from Toronto/Lester B. Pearson International Airport to Hong Kong, a Cathay Pacific Airways Airbus A340-300, registration B-HXN, experienced an uncommanded shutdown of its number 1 engine. The incident occurred approximately one hour and nine minutes into the flight while cruising at flight level 350. The flight crew reported feeling an airframe vibration followed by the spontaneous loss of engine power.
At the time of the event, the aircraft was carrying 249 passengers and 13 crew members. Because the pilots observed no rotation from the engine's windmilling components, they suspected the engine had seized and elected not to attempt a restart. Following consultation with technical personnel in Hong Kong, the crew diverted the aircraft to Vancouver International Airport, where it landed safely without further incident.
The investigation
Investigators examined the CFM56-5C4 engine and found that the shutdown occurred without any prior cockpit warnings or entries in the centralized fault display system. Post-flight inspections in Vancouver revealed that while the engine had not actually seized, the permanent magnet alternator (PMA) and the electronic control unit (ECU) required replacement. During testing of the replacement components, a second engine shutdown occurred under similar circumstances.
Detailed analysis of the hardware revealed scoring and burning on the PMA rotor and stator, alongside excessive play in the PMA drive shaft. Further examination of the assembly uncovered a visible crack in the ball bearing cage. Additionally, investigators found that the Airbus A340 maintenance manuals lacked specific instructions for checking drive shaft play or identifying rotor scoring, which led maintenance personnel to overlook critical indicators of wear during the initial troubleshooting.
Findings
- The primary cause of the engine shutdown was radial overload stress leading to contact fatigue and spalling in the ball bearing of the PMA drive shaft.
- This mechanical failure caused the PMA rotor to contact the stator, creating an intermittent short circuit that interrupted the electrical power supply to the ECU.
- A known deficiency in the ECU software prevented the system from successfully switching to alternate aircraft electrical power sources during the power loss.
- The lack of specific maintenance references for drive shaft play and rotor scoring hindered the ability of technicians to identify the failing component during the first inspection.