A Serene Air Airbus A330-200, registration AP-BNE performing flight ER-502 from Karachi to Islamabad (Pakistan) with 120 people on board, was already enroute at FL370 about 220nm northeast of Karachi when the crew received an engine (CF6) stall indication, shut the engine down, drifted down to FL220, turned around and returned to Karachi for a safe landing on runway 25L about 40 minutes after leaving FL370.
A passenger reported the captain told them an engine had failed, something that had happened to the aircraft already a few weeks ago, see Incident: Serene A332 near Karachi on Oct 1st 2020, engine shut down in flight.
A replacement Boeing 737-800 registration AP-BNA is just climbing out of Karachi with a delay of about 6 hours.
On Apr 15th 2021 Pakistan's SIB reported an engine #2 (right hand engine) FADEC overheat ECAM message was generated triggering a master caution. The engine was shut down and the aircraft returned to Karachi on single engine. The occurrence was rated a serious incident and is being investigated by the SIB.
On Jun 24th 2021 Germany's BFU reported they are supporting the investigation led by Pakistan's SIB, they have been asked to read out a data medium.
The occurrence aircraft returned to service after about 36 hours on the ground in Karachi.
On Aug 24th 2026 Pakistan's BASIP (Bureau of Aircraft Safety Investigation Pakistan) released their final report concluding the probable causes of the serious incident were:
Cause
The occurrence was caused by overheating of the Engine No. 2 Electronic Control Unit (ECU), which resulted in failure of both ECU Power Supply Modules and the subsequent ENG 2 FADEC FAULT during cruise flight.
Contributory Factors
The ECU overheating was caused by continuous leakage of hot bleed air through a deteriorated Engine No. 2 Thrust Reverser Pressurization Valve (TRPV), which exhibited significant internal wear and leakage of its pressure control components.
Latent Contributory Factors
- Maintenance personnel did not fully accomplish the approved MMEL deactivation procedure for the Engine No. 2 thrust reverser, as the required pneumatic blanking cap was not installed and was replaced with a non-approved polyethylene covering. This maintenance non-compliance removed a designed barrier against hot bleed air discharge and remained undetected prior to the occurrence flight.
- The failure to correct the incomplete accomplishment of the MMEL thrust reverser deactivation procedure indicates a breakdown in maintenance procedural compliance and verification processes, allowing a latent unsafe condition to remain on the aircraft prior to the occurrence flight.
The BASIP analysed:
On 05th April, 2021 Serene Air Airbus 330-200 aircraft bearing Registration No AP-BNE was scheduled for a routine flight SEP-502 from JIAP, Karachi to IIAP, Islamabad. Aircraft landed back at JIAP, Karachi due to In Flight Shut Down (Engine No.2).
During the climb from Karachi to Islamabad, the aircraft experienced a MASTER CAUTION accompanied by an ECAM transition from the CRUISE to ENG page. Although engine parameters remained normal and balanced, a STARTER VALVE 2 FAULT message was recorded and subsequently became invalid. After levelling at FL370, an ENG 2 FADEC FAULT occurred, resulting in the disconnection of the auto-thrust system. Following the fault, Engine No. 2 was shut down and the flight was turned back to JIAP, Karachi. During the descent, the auto-thrust system re-engaged and operated normally. The aircraft subsequently landed at JIAP, Karachi, without an overweight landing.
Flight Operations
Following the occurrence of Engine No. 2 caution messages during the climb, the flight crew monitored engine indications and maintained the climb profile as engine parameters remained within normal limits. Upon the subsequent ENG 2 FADEC FAULT at FL370 and the associated auto-thrust disconnection, as per PFR, ENG2 FADEC FAULT triggered at 08:20 UTC. Then engine #2 experienced a thrust decrease, which led to a yawing moment towards the right. This thrust asymmetry was compensated by left rudder deflection. ENG 1 thrust lever held at TOGA for approximately 10 seconds (s), then returned to MCL; A/THR remained armed but disengaged. In case of non-standard disconnection, a message A/THR OFF is logged into the PFR. As this PFR message is not present, crew has performed an A/THR standard disconnection with the instinctive pushbutton on the thrust levers. The crew carried out the relevant procedures, including shutdown of Engine No. 2. The flight was then discontinued and a return to JIAP, Karachi was initiated. During the descent, Auto-Thrust functionality was restored and remained available for the remainder of the flight. The aircraft completed a single-engine approach and landed at JIAP, Karachi without exceeding the maximum landing weight limitations.
...
Electronic Control Unit
The ECU was sent for tear down investigation where after initial inspection with minor observation of external body the component was subjected to testing. Initially NVM (Non-volatile memory / fault data) retrieval was not possible and unit did not communicate with data loader. Troubleshooting revealed defective PSM (Power Supply Module) on Channel A and Channel B. After replacement of both PSM, NVM retrieval and decode was performed. NVM Data showed several faults on both channels including ECU OVER TEMPERATURE. The reported ENG 2 FADEC Overheat ECAM Master Caution was confirmed by NVM analysis.
Both temperature recorder inside the ECU showed all fields dark, which means internal temperature was over 126°C. The ECU contains two temperature recorders on the plate between Channel-A and Channel-B Circuit Card Assemblies (CCAs). Each temperature recorder is divided into four sections, and each section has a different temperature threshold (76 °C, 93 °C, 110°C, and 126 °C). As each temperature threshold is reached, the temperature recorder section associated with that temperature threshold darkens. We found both temperature recorders dark on all four segments, which indicates that the internal ECU temperature was above 126 °C.
The loss of both PSM is most likely caused by overheat of the ECU. The final temperature was above 126°C, which is outside the specified operating temperature range for electronic parts used in the ECU. As there are no indications that this extreme heat has been generated inside the ECU, therefore, there can only be an external cause for the over heat of the ECU.
...
Human Factors
The crews recognition of abnormal engine indications, adherence to checklists, decision-making, communication with ATC, and execution of the diversion were appropriate and consistent with operator SOPs.
At the time of the occurrence, Engine No. 2 thrust reverser had been deactivated under MMEL provisions. The approved maintenance procedure required installation of a blanking cap on the flexible pneumatic hose between the thrust reverser pressurization valve and the centre drive unit. Post-occurrence examination revealed that this cap had not been installed, as was not available, instead the hose end was covered with a polyethene with the use of tie wrap. The polyethene is not designed to with stand the continuous hot bleed air and created an open pneumatic discharge path within the fan cowl area. Consequently, if pressure were present downstream of the thrust reverser pressurization valve, hot bleed air could be released directly into the nacelle compartment.
A passenger reported the captain told them an engine had failed, something that had happened to the aircraft already a few weeks ago, see Incident: Serene A332 near Karachi on Oct 1st 2020, engine shut down in flight.
A replacement Boeing 737-800 registration AP-BNA is just climbing out of Karachi with a delay of about 6 hours.
On Apr 15th 2021 Pakistan's SIB reported an engine #2 (right hand engine) FADEC overheat ECAM message was generated triggering a master caution. The engine was shut down and the aircraft returned to Karachi on single engine. The occurrence was rated a serious incident and is being investigated by the SIB.
On Jun 24th 2021 Germany's BFU reported they are supporting the investigation led by Pakistan's SIB, they have been asked to read out a data medium.
The occurrence aircraft returned to service after about 36 hours on the ground in Karachi.
On Aug 24th 2026 Pakistan's BASIP (Bureau of Aircraft Safety Investigation Pakistan) released their final report concluding the probable causes of the serious incident were:
Cause
The occurrence was caused by overheating of the Engine No. 2 Electronic Control Unit (ECU), which resulted in failure of both ECU Power Supply Modules and the subsequent ENG 2 FADEC FAULT during cruise flight.
Contributory Factors
The ECU overheating was caused by continuous leakage of hot bleed air through a deteriorated Engine No. 2 Thrust Reverser Pressurization Valve (TRPV), which exhibited significant internal wear and leakage of its pressure control components.
Latent Contributory Factors
- Maintenance personnel did not fully accomplish the approved MMEL deactivation procedure for the Engine No. 2 thrust reverser, as the required pneumatic blanking cap was not installed and was replaced with a non-approved polyethylene covering. This maintenance non-compliance removed a designed barrier against hot bleed air discharge and remained undetected prior to the occurrence flight.
- The failure to correct the incomplete accomplishment of the MMEL thrust reverser deactivation procedure indicates a breakdown in maintenance procedural compliance and verification processes, allowing a latent unsafe condition to remain on the aircraft prior to the occurrence flight.
The BASIP analysed:
On 05th April, 2021 Serene Air Airbus 330-200 aircraft bearing Registration No AP-BNE was scheduled for a routine flight SEP-502 from JIAP, Karachi to IIAP, Islamabad. Aircraft landed back at JIAP, Karachi due to In Flight Shut Down (Engine No.2).
During the climb from Karachi to Islamabad, the aircraft experienced a MASTER CAUTION accompanied by an ECAM transition from the CRUISE to ENG page. Although engine parameters remained normal and balanced, a STARTER VALVE 2 FAULT message was recorded and subsequently became invalid. After levelling at FL370, an ENG 2 FADEC FAULT occurred, resulting in the disconnection of the auto-thrust system. Following the fault, Engine No. 2 was shut down and the flight was turned back to JIAP, Karachi. During the descent, the auto-thrust system re-engaged and operated normally. The aircraft subsequently landed at JIAP, Karachi, without an overweight landing.
Flight Operations
Following the occurrence of Engine No. 2 caution messages during the climb, the flight crew monitored engine indications and maintained the climb profile as engine parameters remained within normal limits. Upon the subsequent ENG 2 FADEC FAULT at FL370 and the associated auto-thrust disconnection, as per PFR, ENG2 FADEC FAULT triggered at 08:20 UTC. Then engine #2 experienced a thrust decrease, which led to a yawing moment towards the right. This thrust asymmetry was compensated by left rudder deflection. ENG 1 thrust lever held at TOGA for approximately 10 seconds (s), then returned to MCL; A/THR remained armed but disengaged. In case of non-standard disconnection, a message A/THR OFF is logged into the PFR. As this PFR message is not present, crew has performed an A/THR standard disconnection with the instinctive pushbutton on the thrust levers. The crew carried out the relevant procedures, including shutdown of Engine No. 2. The flight was then discontinued and a return to JIAP, Karachi was initiated. During the descent, Auto-Thrust functionality was restored and remained available for the remainder of the flight. The aircraft completed a single-engine approach and landed at JIAP, Karachi without exceeding the maximum landing weight limitations.
...
Electronic Control Unit
The ECU was sent for tear down investigation where after initial inspection with minor observation of external body the component was subjected to testing. Initially NVM (Non-volatile memory / fault data) retrieval was not possible and unit did not communicate with data loader. Troubleshooting revealed defective PSM (Power Supply Module) on Channel A and Channel B. After replacement of both PSM, NVM retrieval and decode was performed. NVM Data showed several faults on both channels including ECU OVER TEMPERATURE. The reported ENG 2 FADEC Overheat ECAM Master Caution was confirmed by NVM analysis.
Both temperature recorder inside the ECU showed all fields dark, which means internal temperature was over 126°C. The ECU contains two temperature recorders on the plate between Channel-A and Channel-B Circuit Card Assemblies (CCAs). Each temperature recorder is divided into four sections, and each section has a different temperature threshold (76 °C, 93 °C, 110°C, and 126 °C). As each temperature threshold is reached, the temperature recorder section associated with that temperature threshold darkens. We found both temperature recorders dark on all four segments, which indicates that the internal ECU temperature was above 126 °C.
The loss of both PSM is most likely caused by overheat of the ECU. The final temperature was above 126°C, which is outside the specified operating temperature range for electronic parts used in the ECU. As there are no indications that this extreme heat has been generated inside the ECU, therefore, there can only be an external cause for the over heat of the ECU.
...
Human Factors
The crews recognition of abnormal engine indications, adherence to checklists, decision-making, communication with ATC, and execution of the diversion were appropriate and consistent with operator SOPs.
At the time of the occurrence, Engine No. 2 thrust reverser had been deactivated under MMEL provisions. The approved maintenance procedure required installation of a blanking cap on the flexible pneumatic hose between the thrust reverser pressurization valve and the centre drive unit. Post-occurrence examination revealed that this cap had not been installed, as was not available, instead the hose end was covered with a polyethene with the use of tie wrap. The polyethene is not designed to with stand the continuous hot bleed air and created an open pneumatic discharge path within the fan cowl area. Consequently, if pressure were present downstream of the thrust reverser pressurization valve, hot bleed air could be released directly into the nacelle compartment.
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