Introduction
On 11 March 2025, a TAP Air Portugal Airbus A321-200neo, registration CS-TJQ, operating flight TP-1356 from Lisbon Humberto Delgado Airport (LIS), Portugal, to London Heathrow Airport (LHR), United Kingdom, declared an emergency due to smoke in the cabin and cockpit.
The aircraft was cruising at FL360 (36,000 feet) approximately 150 nautical miles west-northwest of Porto, Portugal, in Spanish airspace when the crew reported the presence of smoke on board and requested an immediate diversion to Porto Francisco Sá Carneiro Airport (OPO), Portugal.
The aircraft landed safely on Runway 35 at Porto approximately 40 minutes after the emergency declaration. Upon arrival, nine occupants, including passengers and crew, were transported to local hospitals due to smoke inhalation.
TAP Air Portugal later confirmed the flight was diverted due to a technical issue, and a replacement aircraft, an Airbus A321-200 (CS-TJH), was dispatched to continue the journey to London Heathrow with a delay of approximately 5 hours and 30 minutes.
The affected aircraft remained grounded in Porto for further inspection and investigation.
Sequence of Events
Departure and Cruise Phase
• The Airbus A321neo departed Lisbon (LIS) on schedule, climbing to its planned cruising altitude of FL360.
• The flight crew reported normal operations until approximately 150nm west-northwest of Porto, when smoke became noticeable in the cabin and cockpit.
Emergency Declaration and Diversion to Porto
• The crew declared an emergency and coordinated with Spanish and Portuguese ATC for an expedited diversion.
• Oxygen masks were not deployed, but cabin crew and passengers reported irritation from the smoke.
• ATC cleared the aircraft for an immediate descent and approach to Porto (OPO), prioritising it for landing on Runway 35.
Landing and Emergency Response
• The aircraft touched down safely in Porto approximately 40 minutes after the emergency declaration.
• Airport emergency services were on standby and immediately inspected the aircraft upon arrival.
• Nine occupants were treated for smoke inhalation and transported to local hospitals for further evaluation.
Aircraft and System Information
The Airbus A321-200neo is a modern, fuel-efficient narrow-body aircraft powered by CFM LEAP-1A or Pratt & Whitney PW1100G engines.
The aircraft’s cabin is equipped with advanced air filtration and smoke detection systems, which are designed to identify and contain potential fire or smoke-related hazards.
Smoke in the cabin can originate from various sources, including:
• Electrical system failures (wiring short circuits, avionics overheating)
• Overheated cabin components (galleys, air conditioning packs, or overhead panels)
• Hydraulic fluid or oil leakage into the bleed air system
• Passenger lithium battery fire or malfunctioning personal electronic devices
Potential Causes and Investigation Focus
Following the incident, TAP Air Portugal, Airbus technical teams, and Portuguese aviation authorities initiated an investigation to determine the source of the smoke.
Possible Causes Under Examination
1. Electrical Fault or Short Circuit
• Electrical failures, particularly in avionics or cabin panel wiring, are a common cause of in-flight smoke events.
• The A321neo’s modern avionics suite includes multiple electrical components that could have overheated or suffered an insulation failure.
2. Bleed Air Contamination (Engine Oil or Hydraulic Fluid Leak)
• A known issue in modern aircraft is contaminated bleed air entering the cabin ventilation system due to oil or hydraulic leaks from the engines.
• If engine seals fail, oil mist can be drawn into the air conditioning system, producing a smoke-like haze and strong odour.
3. Fault in the Air Conditioning System (Environmental Control System – ECS)
• The A321neo’s ECS is responsible for regulating cabin temperature and air distribution.
• A failure in one of the air conditioning packs could lead to overheating, potentially causing smoke or fumes to circulate throughout the cabin.
4. Passenger Lithium Battery Fire (Overheated Power Bank or Device)
• Lithium-ion battery fires are a growing concern in aviation safety.
• A malfunctioning passenger device, such as a laptop, phone, or power bank, may have caused a thermal event in an overhead bin or under a seat.
Key Safety Concerns and Implications
1. Smoke-Related Emergency Procedures
• Smoke on board is considered one of the most serious in-flight emergencies due to its potential to obscure visibility, incapacitate crew, or indicate an onboard fire.
• The crew’s decision to divert immediately was appropriate, minimising further exposure and ensuring a swift emergency response.
2. Passenger and Crew Health Risks
• The nine individuals taken to hospital suggest significant smoke inhalation exposure.
• If toxic fumes were present, further medical monitoring and toxicology assessments may be required.
3. Aircraft Systems Reliability
• If a mechanical or electrical fault caused the smoke event, inspections of similar aircraft in TAP’s fleet may be necessary to prevent recurrence.
• Airbus may issue revised maintenance procedures or software updates to address system vulnerabilities.
Maintenance and Investigation Actions
Upon arrival in Porto, TAP Air Portugal’s engineering team, along with aviation safety inspectors, performed a detailed examination of the aircraft.
Initial Inspection Procedures
1. Avionics and Electrical System Check
• Engineers inspected cockpit wiring, avionics cooling fans, and power distribution units for evidence of overheating.
2. Bleed Air and Engine System Examination
• Engines, bleed air lines, and air conditioning packs were checked for leaks or contamination of the ECS system.
3. Cabin and Cargo Area Inspection
• Investigators checked for burn marks, melted components, or foreign object damage in cabin panels and luggage compartments.
4. Passenger Electronic Device Analysis
• Cabin crew provided statements regarding any unusual activity or devices that may have malfunctioned.
As of the latest update, the aircraft remains grounded for further evaluation. The exact cause of the smoke event has not yet been confirmed.
Safety Recommendations and Preventative Measures
1. Enhanced Smoke Detection and Response Training
• Airline crews should receive enhanced training for early smoke detection and rapid emergency decision-making.
• Cabin crew procedures should be updated to prioritise locating the source of smoke and isolating it if possible.
2. Improved Cabin Air Quality Monitoring
• More sensitive air quality monitoring sensors in the ECS could detect anomalies sooner and alert crews before smoke reaches the cabin.
3. Stricter Lithium Battery Regulations for Passengers
• Airlines should reinforce policies regarding lithium battery handling, ensuring passengers understand the risks of overheating power banks and electronic devices.
• Cabin crew should be equipped with more fire containment kits to manage potential thermal runaway events.
Conclusion
TAP Air Portugal flight TP-1356 was forced to make an emergency diversion to Porto due to smoke in the cabin and cockpit while en route to London Heathrow.
The crew acted swiftly and professionally, ensuring a safe landing. However, nine individuals required medical attention for smoke inhalation, underscoring the seriousness of the incident.
The exact cause of the smoke remains under investigation, with possibilities including an electrical fault, bleed air contamination, or a passenger lithium battery fire.
TAP Air Portugal and aviation safety authorities will continue to assess the aircraft to determine the root cause and implement necessary corrective actions to prevent future occurrences.
Disclaimer
“This report is based on publicly available information and investigations as of 12 March 2025. While every effort has been made to ensure accuracy, we cannot guarantee the completeness of the details provided. If you are the rightful owner of any referenced materials and wish for them to be removed, please email takedown@cockpitking.com.”
