Flight DL-353 | Registration: N141DU
Date: 19 March 2025 | Location: San Francisco, California, USA
Introduction
On 19 March 2025, a Delta Airlines Bombardier CS100 (Airbus A220-100), registration N141DU, operating flight DL-353 from San Francisco International Airport (KSFO) to Seattle-Tacoma International Airport (KSEA), declared an emergency shortly after departure due to reports of fumes in the cabin and cockpit. The aircraft, carrying 116 occupants, was climbing through FL210 when the crew donned oxygen masks and halted the climb. Several passengers reported symptoms consistent with respiratory irritation.
The flight crew returned to San Francisco and landed safely on runway 28R approximately 30 minutes after takeoff. Emergency services were requested on arrival. A replacement aircraft was dispatched, and the occurrence aircraft was withdrawn from service for inspection.
Flight Details
• Aircraft Type: Bombardier CS100 (Airbus A220-100)
• Engines: 2 × Pratt & Whitney PW1500G
• Operator: Delta Airlines
• Tail Number: N141DU
• Flight Number: DL-353
• Departure Airport: San Francisco International Airport (KSFO), California, USA
• Destination Airport: Seattle-Tacoma International Airport (KSEA), Washington, USA
• Date of Event: 19 March 2025
• Occupants: 116 (including passengers and crew)
• Phase of Flight: Initial climb
• Cruising Altitude Reached: FL210
• Time to Return: ~30 minutes after departure
Sequence of Events
Takeoff and Climb
Flight DL-353 departed San Francisco’s runway 28L and began a normal initial climb towards its planned cruising altitude. Shortly after passing through 21,000 feet, the flight crew began detecting an unusual odour and reported the presence of fumes in the cockpit and cabin. In accordance with Delta’s emergency protocols and Airbus A220 (CS100) standard operating procedures, the flight crew donned oxygen masks and declared an emergency.
Onboard Conditions and Passenger Impact
The cabin crew began to observe multiple passengers complaining of respiratory irritation and lung discomfort. Although the severity of symptoms varied, the captain requested emergency medical assistance to meet the aircraft on arrival. Cabin air contamination events such as this can involve volatile compounds from engine oils, hydraulic fluid, or ozone conversion system faults—though the exact source in this case remains under investigation.
Return and Landing
The flight was cleared to return to San Francisco and landed without further incident on runway 28R. The aircraft was met by emergency response units including paramedics, who evaluated several passengers and crew members. No hospitalisations were reported, but multiple passengers received treatment for symptoms consistent with minor lung and airway irritation.
Immediate Actions and Aircraft Status
• Aircraft Withdrawal: Following the event, the aircraft (N141DU) was taken out of service for engineering inspection and air quality sampling.
• Replacement Aircraft: Delta dispatched a substitute CS100 (N104DU), which departed later and reached Seattle with a delay of approximately 15 hours.
• Maintenance and Return to Service: After evaluation and precautionary system flushes, N141DU was repositioned to Minneapolis on 22 March 2025 and returned to commercial service the following day.
Technical and Safety Considerations
Cabin Fume Events
Cabin fume events are an established concern in modern aviation and are typically related to:
• Oil seal leaks in engines or APU systems causing bleed air contamination.
• Hydraulic or de-icing fluid leaks entering the air conditioning system.
• Electrical faults leading to burning odours from wiring insulation.
• Ozone converter malfunctions leading to unneutralised atmospheric ozone causing respiratory effects.
The A220/CS100, like most modern jets, uses bleed air from the engines to pressurise and ventilate the cabin. A failure in bleed air filtration or environmental control systems (ECS) could permit harmful vapours to circulate throughout the aircraft interior.
Detection and Response
Delta’s flight crew followed established procedures, donning masks and requesting immediate medical support. The aircraft’s Environmental Control System (ECS), avionics logs, and cockpit voice recorder (CVR) were likely reviewed during the post-incident investigation. No structural damage was reported.
Investigation and Follow-Up
As of 31 March 2025:
• Formal Classification: The occurrence has been treated as an accident due to passenger injuries and aircraft system malfunction.
• Regulatory Involvement: The FAA has been notified and is working in coordination with Delta Airlines to determine the source of the fumes.
• Operator Actions: Delta has initiated a fleet-wide inspection of ECS-related components in its A220 fleet.
• Passenger Safety: No serious injuries were reported, though the event prompted increased scrutiny of cabin air quality and filtration systems.
Summary and Safety Outlook
This accident highlights ongoing industry concerns about fume events, particularly in aircraft that use engine bleed air for cabin pressurisation. While no passengers or crew suffered lasting harm, the impact on flight safety and passenger health required immediate diversion and regulatory reporting.
Further data analysis, including air sample testing, maintenance logs, and flight deck system alerts, will be critical to determining root cause. The A220 has a strong safety record, but operators remain vigilant in monitoring ECS integrity.
Disclaimer
This report is based on publicly available information and statements from official sources as of 31 March 2025. The content may be updated as more details emerge. If you are the rightful owner of any referenced content and wish for it to be removed, please contact takedown@cockpitking.com.
