Date: 7th December 2024
Location: San Francisco International Airport (SFO), California, USA
Aircraft: Boeing 737-900, registration N37420
Operator: United Airlines
Flight Number: UA-1898
Route: San Francisco (SFO) to Denver (DEN)
Occupants: 187 (Passengers and Crew)
Injuries: None reported
Summary of Events
On 7th December 2024, United Airlines flight UA-1898, a Boeing 737-900, experienced a surge in the left-hand engine (CFM56) shortly after takeoff from San Francisco International Airport. The crew stopped the climb at 3000 feet and elected to return to the airport. While on approach, the airport tower observed flames emanating from the left engine, prompting an emergency response. The engine later appeared to stabilize, but the crew shut it down as a precaution. The aircraft landed safely on San Francisco’s runway 28R approximately 10 minutes after departure.
A replacement Airbus A321-200N completed the flight to Denver, departing with an 8-hour delay. The incident aircraft remained grounded at San Francisco for further investigation and maintenance.
Aircraft Information
• Type: Boeing 737-900
• Engine: CFM56-7B27
• Registration: N37420
The Boeing 737-900, part of the 737NG series, is equipped with CFM56-7B engines, known for their reliability. However, high-performance engines are subject to operational stresses that can result in surges or other anomalies.
Sequence of Events
1. Takeoff and Climb:
• The aircraft departed San Francisco’s runway 01L as planned, climbing to an initial altitude of 3000 feet.
2. Engine Surge and Tower Observation:
• The crew reported a surge in the left-hand engine and informed air traffic control of their intent to return.
• Tower personnel observed flames emanating from the affected engine and alerted emergency services.
3. Engine Shutdown and Return:
• Shortly after the initial fire observation, the flames ceased, and the engine appeared normal.
• As a precaution, the crew shut down the left-hand engine and continued the return to SFO.
4. Landing and Post-Incident Actions:
• The aircraft landed safely on runway 28R approximately 10 minutes after departure.
• Emergency services inspected the aircraft upon landing.
• The passengers were deplaned and transferred to a replacement aircraft for onward travel.
Initial Findings
• Engine Surge:
• A surge in the left-hand engine, likely due to an internal airflow disruption, led to the initial fire and vibration.
• Engine Fire:
• Flames were observed from the engine, indicating a potential combustion anomaly. The fire self-extinguished, and no visible damage was reported post-landing.
• Crew Response:
• The crew followed standard operating procedures, shutting down the affected engine and prioritizing passenger safety.
Safety Risks
1. Engine Malfunction:
• A surge or fire in a high-bypass turbofan engine can escalate into a more severe failure if not promptly managed.
2. Passenger Safety:
• In-flight engine failures pose risks to cabin pressurization, structural integrity, and operational control.
3. Operational Disruption:
• Grounding the aircraft resulted in a significant delay for passengers and operational complications for the airline.
Recommendations
1. Engine Inspection and Maintenance:
• Conduct a thorough inspection of the left-hand engine, including compressor and combustion chamber components, to identify the root cause of the surge.
2. Enhanced Crew Training:
• Reassess crew protocols for engine malfunctions and emergency landings to ensure rapid and effective responses.
3. Data Sharing:
• Report the incident to CFM International for potential fleet-wide advisories or technical updates.
4. Passenger Communication:
• Enhance procedures for informing passengers during technical issues to maintain trust and minimize anxiety.
Safety Lessons
This incident highlights the importance of robust engine design, regular maintenance, and rigorous crew training. Prompt decision-making by the flight crew ensured a safe outcome, demonstrating the value of adhering to established safety protocols.
Disclaimer
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Our investigation reports are based on all the evidence and facts available at the time of writing and posting. We apologise if any details are missed or are not fully accurate.
