Flight AF-374 | Registration: F-HTYH
Date: 6 April 2025 | Location: North Atlantic Airspace near Shannon, Ireland
Flight Details
• Aircraft Type: Airbus A350-900
• Engines: 2 × Rolls-Royce Trent XWB-84
• Operator: Air France
• Registration: F-HTYH
• Flight Number: AF-374
• Callsign: AFR374
• Route: Paris Charles de Gaulle (LFPG), France to Vancouver International (CYVR), Canada
• Date of Incident: 6 April 2025
• Total Occupants: 296 (280 passengers, 16 crew)
• Weather Conditions: VMC, no known atmospheric anomalies reported over Irish FIR
Introduction
On 6 April 2025, an Air France Airbus A350-900 operating flight AF-374 from Paris to Vancouver declared a PAN PAN emergency while in cruise near the boundary of Shanwick Oceanic airspace. The crew reported an unidentified odour on board and requested an immediate return to Paris Charles de Gaulle. The aircraft descended to FL100 and landed safely in Paris approximately 3.5 hours after departure. The event prompted a full technical investigation and precautionary aircraft replacement.
Sequence of Events
AF-374 departed Paris Charles de Gaulle in the early afternoon and climbed to its cruise altitude of FL380. Approximately 260 nautical miles north-northwest of Shannon, just prior to entering Oceanic airspace, the flight crew contacted ATC to declare a PAN PAN emergency, citing an unidentified odour in the cabin or cockpit environment.
Following the declaration, the crew requested a descent to FL100, which was coordinated with Shannon Control and approved. The aircraft exited its cruise altitude, maintained communications with ATC, and rerouted eastbound, entering Irish and subsequently French airspace under normal flight conditions.
The descent to FL100 was precautionary, consistent with procedures for suspected fume events or cabin air contamination, to ensure pressurisation safety and limit exposure to unknown substances.
The aircraft landed on runway 27L at Paris CDG without further incident. Emergency services were on standby but did not need to intervene. The aircraft taxied to a remote stand for inspection.
Crew & Communication
The crew followed standard protocols for fume or odour detection events, which prioritise:
• Cabin crew reports or pilot detection of the odour
• Activation of air recirculation and filtration isolation
• Masking as necessary
• Coordination with ATC for descent to a breathable altitude
The decision to declare PAN PAN (urgency) rather than MAYDAY (distress) reflects the absence of incapacitation or fire. Communications with ATC were described as clear and coordinated throughout the deviation and descent.
All transmissions were compliant with ICAO urgency handling phraseology, and the crew maintained full control of the aircraft.
Aircraft Systems & Technical Analysis
The Airbus A350 is equipped with advanced environmental control systems (ECS) that manage airflow, pressurisation, and air quality through high-efficiency particulate air (HEPA) filters and recirculation fans. Air is supplied from engine bleed sources and supplemented via cabin filters.
Unidentified odours on board can result from:
• Contaminated bleed air (e.g. oil or hydraulic fluid leaks)
• Electrical component overheating
• Air conditioning pack malfunction
• Lavatory or galley odours being misrouted into the cabin
• External environmental contaminants entering intake ducts
In this case, the lack of smoke or visible contamination suggests a low-level odour of uncertain origin, possibly linked to environmental systems.
Upon return, the aircraft was withdrawn from service for:
• ECS and air distribution system inspection
• Engine oil seals and bleed air check
• Recirculation fan module analysis
• Cabin material and electrical component review
• Air sampling and cockpit environmental monitoring
Given the duration of grounding and replacement dispatch, initial diagnostics may not have revealed an obvious source, prompting deeper component-level investigation.
Passenger Experience & Cabin Conditions
No injuries or onboard medical events were reported. Some passengers may have noticed an unusual smell depending on its origin and dispersion in the cabin, but no mass symptoms or respiratory distress occurred.
Cabin crew likely reassured passengers following the deviation, and standard emergency procedures were not escalated. The descent to FL100 may have caused minor discomfort or extended flight duration, but conditions remained stable.
Passengers were later transferred to a replacement aircraft, which arrived in Vancouver with an estimated 8-hour delay.
Emergency Response & Aftermath
Paris emergency services met the aircraft as a precaution. No evacuations were carried out, and the aircraft taxied without external assistance.
Following disembarkation, F-HTYH was positioned in a technical bay for maintenance. The replacement aircraft, A350 F-HTYQ, was dispatched later the same day to resume service, minimising network disruption.
Air France initiated internal incident and engineering reports in coordination with Airbus and Rolls-Royce technical support.
Investigation Status
No formal investigation has been announced by French BEA, indicating the event is being handled as an operational safety issue rather than a reportable accident or serious incident under Annex 13 criteria.
The airline’s safety department, in coordination with maintenance control and cabin operations, will analyse:
• Crew reports
• Maintenance history
• Previous occurrences of similar odours
• BITE logs from ECS and cabin pressurisation systems
If a systemic fault or recurring design issue is detected, a safety bulletin may be issued to other A350 operators.
Root Cause & Contributing Factors
The precise cause of the odour remains under investigation. Likely scenarios include:
• Trace contamination of bleed air from an oil seal leak
• Overheated electrical components in the galley or avionics bay
• Fan or air conditioning pack malfunction
• External airborne contaminant briefly entering air intake zones
Contributing factors may include:
• Inability to isolate the odour source inflight
• Proximity to North Atlantic tracks, necessitating decisive action before entry
• Safety culture favouring return before committing to extended oceanic crossing
Safety Recommendations & Industry Impact
This incident underscores the following safety considerations:
• Value of crew vigilance regarding air quality
• Importance of early PAN declarations before oceanic crossings
• Maintenance of detailed cabin environment monitoring systems
• Review of ECS and bleed air fault isolation procedures
Airlines operating long-haul aircraft are reminded to train crew in the escalation path for odour and fume events and to ensure ECS maintenance records are current and complete.
If an ECS or engine seal fault is confirmed, component manufacturers may revise inspection intervals or issue service bulletins for pre-emptive replacement.
Conclusion
Flight AF-374’s return due to an unidentified odour illustrates the importance of conservative decision-making in transatlantic operations. While the issue did not result in injuries or mechanical failure, the pre-emptive return to base protected passenger safety and enabled controlled technical evaluation.
Modern long-range aircraft like the A350 rely heavily on sophisticated air systems, and even minor deviations from normal air quality can merit significant operational response. The case reinforces industry-wide best practices in environmental system monitoring and procedural discipline.
Disclaimer
This article is based on publicly available information and reports at the time of writing. While every effort has been made to ensure accuracy, we cannot guarantee the completeness of the information provided.
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