Overview
On October 31, 2024, Avianca flight AV-46, a Boeing 787-8 registered N785AV, experienced a loss of cabin pressure during cruise at FL420 over the Atlantic Ocean, approximately 520nm south of Ponta Delgada, Portugal. The flight, en route from Bogotá, Colombia (SKBO) to Madrid, Spain (LEMD), conducted an emergency descent to FL100 and diverted to Ponta Delgada, where it landed safely. No injuries were reported among the 250 passengers and 9 crew members.
Incident Summary
Flight Details
• Aircraft Type: Boeing 787-8
• Registration: N785AV
• Flight Number: AV-46
• Operator: Avianca
• Departure Airport: El Dorado International Airport (SKBO), Bogotá, Colombia
• Destination Airport: Adolfo Suárez Madrid-Barajas Airport (LEMD), Madrid, Spain
• Alternate Airport: João Paulo II Airport (LPPD), Ponta Delgada, Portugal
• People Onboard: 250 passengers, 9 crew
Sequence of Events
1. The aircraft departed Bogotá at 13:20 UTC for an anticipated 10-hour flight to Madrid.
2. At FL420, the crew received an L GEN DRIVE L2 alarm, followed by a Left PACK failure indication.
3. The APU was activated, and the crew began a descent to FL410.
4. As the cabin altitude rose to 10,100 feet, the CABIN ALTITUDE warning triggered.
5. The crew initiated an emergency descent to FL100, manually deployed passenger oxygen masks, and declared an emergency via CPDLC, VHF, and HF.
6. The aircraft diverted to Ponta Delgada and landed safely on runway 12 at 19:55 UTC, approximately 90 minutes after the onset of the incident.
Technical Analysis
Aircraft Systems
The Boeing 787’s pressurisation system is fully electric, powered by four Variable Frequency Starter Generators (VFSG), two on each engine. These provide power to four Cabin Air Compressors (CACs), which supply pressurised air to two air conditioning packs for cabin pressurisation.
Sequence of Failures
1. VFSG L2 Failure: The failure of the left-side generator caused a power loss to the CAC L2.
2. Cascade Shutdown: The Pack Control Unit (PCU) attempted to restart CAC L2, which caused an overload, leading to the shutdown of CAC L1.
3. RH Pack Issues: The right-hand pack, designed to compensate for single-pack failures, was found to be underperforming due to a misassembled recirculation duct, resulting in a significant air leak.
Contributing Factors
• Maintenance Errors: The depressurisation event occurred on the third flight after major maintenance work on the Packs. The misassembled recirculation duct compromised the right-hand pack’s functionality.
• Component Reliability: The VFSG L2 failure initiated the cascade of events, and further analysis of the generator is underway by the manufacturer.
• Operational Context: The RH Pack’s diminished capacity limited the system’s ability to manage pressurisation following the LH Pack failure.
Crew and Maintenance Response
Crew Actions
• APU Activation: Provided auxiliary power to sustain systems.
• Emergency Descent: Executed promptly to FL100, ensuring passenger and crew safety.
• Oxygen Deployment: Passenger oxygen masks were manually deployed as a precaution, even though cabin altitude remained below 14,000 feet.
• Diversion Decision: Coordination with operations led to the selection of Ponta Delgada as the alternate airport.
Maintenance Findings
• Post-incident investigation revealed misassembly of recirculation ducts during recent maintenance, causing significant air leaks.
• Maintenance personnel cited limited access to the RH Pack area as a contributing factor to the improper assembly.
• The failed generator was sent to the manufacturer, CRANE, for failure mode analysis.
Safety Implications
Immediate Actions
1. Inspection of Packs: Comprehensive inspection of both LH and RH Packs, focusing on proper assembly and component integrity.
2. Generator Analysis: Investigation of VFSG L2 failure to identify potential design or manufacturing issues.
3. Crew Training: Reinforcement of emergency descent procedures and oxygen deployment protocols.
Long-Term Recommendations
1. Maintenance Protocols: Enhanced quality control measures for critical components like recirculation ducts.
2. Design Improvements: Collaboration with Boeing to address cascading failures within the Pack Control Unit.
3. Operational Reviews: Evaluation of alternate airport selection and fuel management for transoceanic flights.
Conclusion
The incident highlights the critical role of both maintenance accuracy and crew response in managing in-flight emergencies. The Avianca crew’s prompt actions ensured the safety of all occupants. Ongoing investigations by the GPIAA, Avianca, and Boeing aim to address the systemic and operational factors contributing to this event.
Disclaimer
This report is based on all available evidence and facts at the time of writing. While every effort has been made to ensure accuracy, we apologise if any details are missed or not fully accurate. If you are the rightful owner of any associated images and wish for their removal, please email takedown@cockpitking.com.
