Flight Details
Aircraft Type: Boeing 737-824 Operator: United Airlines Registration: N27213 Flight Number: UA2325 Route: Denver International Airport (DEN), Colorado, USA to Edmonton International Airport (YEG), Alberta, Canada Date of Incident: 13 April 2025 Total Occupants: 159 (153 passengers, 6 crew) Weather Conditions: Visual meteorological conditions at departure; no adverse conditions reported
Introduction
On 13 April 2025, a United Airlines Boeing 737-800 operating flight UA2325 declared a Mayday shortly after take-off from Denver due to an in-flight engine shutdown and visible fire. The aircraft, climbing through initial departure altitude from runway 34L, experienced a loss of thrust on the right-hand engine (CFM56-7B26), followed by reports of flame emission from the wing area. The crew levelled off, requested holding to run checklists, and executed a safe return to Denver approximately 40 minutes after departure. Ground observers witnessed flames emanating from the right engine, and the FAA later confirmed that the incident was triggered by a wildlife strike — involving a rabbit during the take-off roll.
Sequence of Events
Flight UA2325 departed Denver International Airport on a scheduled international service to Edmonton. The aircraft lifted off from runway 34L and was in the initial climb phase when the flight crew contacted departure control and issued a Mayday call, reporting an engine failure on the right-hand side.
Within seconds, the crew added that they were also managing a possible fire at the wing, consistent with flame observations. The aircraft stopped climbing at an intermediate altitude and requested vectors to a holding pattern to troubleshoot and complete emergency procedures.
Flight data suggests that the crew entered a hold east of the airport while executing the engine fire checklist. Engine fire bottles may have been discharged, though this has not been officially confirmed.
After stabilising the situation and verifying system integrity, the crew coordinated for a return to runway 34L. The aircraft landed safely approximately 40 minutes after take-off and was met by airport emergency services. No injuries occurred.
Crew & Communication
The crew’s prompt declaration of Mayday reflects a clear and decisive response to a high-risk in-flight emergency. The decision to hold rather than initiate an immediate return suggests situational control and adherence to Boeing’s engine fire and failure protocols.
Crew communication with Denver Departure was concise, and they provided updates regarding fire indications and checklist progress. The holding pattern allowed them time to:
Confirm fire warning indicators Execute memory items for engine fire Verify extinguishing agent activation Assess systems and performance on single-engine operation
At no time was the aircraft declared uncontrollable, and systems such as hydraulics and electrics remained online.
Aircraft Systems & Technical Analysis
The Boeing 737-800 is powered by two CFM56-7B turbofan engines. In this incident, the right engine failed during the take-off phase and exhibited fire indications. Ground witnesses observed three clear bursts of flame from the engine, corroborating crew reports.
On 17 April 2025, the FAA confirmed the cause: wildlife strike involving a rabbit, which was struck during the take-off roll. The impact, though on the ground, likely resulted in ingestion of organic material or a delayed thermal imbalance that led to fire or mechanical disintegration shortly after lift-off.
Key systems affected or activated include:
Engine Fire Detection and Extinguishing System Engine Performance Monitoring (EICAS alerts) Automatic shutdown logic (in case of severe vibration or overspeed) Fuel and hydraulic isolations linked to fire suppression
The engine would have been shut down manually by the crew or automatically by protective logic. The fire detection loop in the engine nacelle is capable of identifying rapid temperature spikes and triggering the necessary cockpit indications.
Post-incident maintenance will include:
Full engine teardown and inspection Verification of nacelle fire damage Inspection of engine mounts and wing structures Wildlife residue analysis and DNA confirmation
The aircraft remained grounded following the incident, and no return-to-service timeline was issued at the time of reporting.
Passenger Experience & Cabin Conditions
Passengers onboard reported feeling a sudden jolt followed by a low-frequency vibration shortly after take-off. Those seated on the right side of the aircraft observed flames trailing the engine in bursts. The cabin crew remained composed and followed established procedures, keeping passengers informed and calm.
There were no oxygen mask deployments, no cabin smoke, and no decompression. The passenger experience, while alarming, was managed professionally with no medical events reported.
Upon landing, the aircraft vacated the runway under its own power and came to a stop clear of the active area. Emergency services inspected the aircraft before clearance to taxi to the gate.
Emergency Response & Aftermath
Denver Airport ARFF units were positioned along runway 34L prior to landing. Upon touchdown, they followed the aircraft to assess any remaining fire risk or signs of exterior damage. No fuel leaks, fire, or nacelle breach were noted after landing.
The affected aircraft, N27213, remained on the ground following the event and underwent detailed inspection by United maintenance personnel and Boeing technical advisors.
A replacement Boeing 737-800, registration N79541, completed the flight to Edmonton with an overall delay of approximately three hours.
Investigation Status
The FAA issued a public statement confirming the engine fire was precipitated by a rabbit strike during the take-off roll. This type of wildlife encounter is rare for jetliners but can be catastrophic depending on timing, location, and mass of the animal.
The FAA will oversee inspection and clearance of the aircraft, while United Airlines’ Safety and Maintenance Engineering divisions are conducting a parallel internal review.
Boeing may issue advisory bulletins if inspection data indicates any systemic vulnerability in the nacelle structure or fire suppression system response time.
Root Cause & Contributing Factors
Primary Cause: Wildlife strike involving a rabbit during take-off, leading to right engine failure and subsequent fire Contributing Factors: Limited wildlife management awareness during low-traffic periods Time of day and runway occupancy by small mammals Potential delay in post-winter wildlife control patrols
The timing of the incident during spring coincides with increased animal activity near airport perimeters, especially at dawn or dusk.
Safety Recommendations & Industry Impact
This incident highlights the ongoing risk of wildlife hazards at major airports, even those with robust mitigation programmes. While birdstrikes are well-documented, mammal strikes — particularly involving small species like rabbits — remain difficult to predict and prevent entirely.
Recommendations likely to arise include:
Enhanced runway sweep protocols, especially before first wave departures Use of thermal or motion-sensor technology to detect small animals Collaboration between wildlife biologists and airport operations teams to review local wildlife patterns Ensuring jet blast zones and under-fence gaps are regularly inspected for animal access routes
Conclusion
The emergency return of United Airlines flight UA2325 following a right engine fire was handled with professionalism and urgency. The cause — a rabbit strike during take-off — underscores a lesser-known but serious hazard in airport operations.
Through swift crew action, effective systems design, and procedural compliance, the aircraft returned safely with no injuries and minimal disruption. The incident serves as a reminder that even the most advanced aircraft remain vulnerable to unpredictable encounters with nature, demanding constant vigilance both in the cockpit and on the ground.
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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