Flight Details
Aircraft Type: Bombardier CRJ-900
Operator: Endeavor Air (on behalf of Delta Air Lines)
Registration: N934XJ
Flight Number: DL-4985
Route: New York John F. Kennedy (JFK) to Cincinnati/Northern Kentucky International Airport (CVG)
Date of Incident: 30 April 2025
Total Occupants: 64 passengers, 4 crew
Weather Conditions: Stable, VMC reported during approach
Introduction
On 30 April 2025, a Canadair Regional Jet CRJ-900 operated by Endeavor Air for Delta Air Lines experienced an in-flight alert during final approach to Cincinnati/Northern Kentucky International Airport. The crew received a smoke detector activation warning from the aft lavatory system while descending through the final approach fix for runway 36R. Although no visible smoke or odour was ultimately detected, the alert prompted a heightened level of crew awareness and was treated in accordance with onboard smoke/fire checklist protocols.
The event was classified as an incident. No injuries were reported among the 64 passengers and four crew members onboard. The aircraft landed without further complications and taxied to a remote stand, where passengers were deplaned by bus and transported to the terminal.
Sequence of Events
Flight DL-4985 departed from JFK Airport in New York on schedule, operating as a short-haul regional service to Cincinnati under normal operating conditions. The aircraft, a CRJ-900 bearing registration N934XJ, had no reported maintenance issues prior to departure, and all pre-flight checks were completed without discrepancy.
Cruise at FL340 was uneventful. The descent and approach phase commenced approximately 80 nautical miles northeast of Cincinnati. Weather along the STAR (Standard Terminal Arrival Route) was stable, with light winds and no significant turbulence reported.
At approximately 15:36 local time, as the aircraft was established on the final approach to runway 36R, the flight deck received an ECAM (Electronic Centralised Aircraft Monitoring) alert indicating a lavatory smoke detector activation in the aft lavatory compartment. The captain, acting as Pilot Flying (PF), handed control to the First Officer, allowing the Pilot Monitoring (PM) to reference the Smoke/Fumes checklist and coordinate with the cabin crew.
At this stage, the cabin crew was instructed to check the aft lavatory for signs of smoke or burning odour. Initial visual checks revealed no abnormalities. The cabin crew opened the lavatory door and scanned the ceiling panels and wall areas for possible signs of thermal runaway from a personal electronic device or fixture malfunction, but nothing was visible or detectable by smell. The crew reported no heat, haze, or odour from within the compartment.
With the aircraft already committed to the final approach, the decision was made to continue for a normal landing while maintaining precautionary coordination with ATC and ground emergency services.
Crew & Communication
Communication between the flight deck and air traffic control remained calm and coordinated. The crew did not declare an emergency but did notify ATC of the smoke detector activation and requested that emergency services stand by upon arrival, as per standard operating procedures for such alerts.
CRM (Crew Resource Management) between the pilots and cabin crew remained highly effective. Upon receiving the ECAM alert, the cabin crew reacted quickly and methodically, using portable fire extinguishers and personal protective breathing equipment as a precaution during inspection of the lavatory area.
The crew maintained a high level of communication throughout the approach phase, with cabin crew providing minute-by-minute updates to the cockpit and ATC kept informed of the unfolding situation.
Upon landing on runway 36R, the aircraft exited the runway via high-speed taxiway and held on a remote stand as emergency personnel conducted an external visual inspection. The cabin crew was instructed to prepare for a possible evacuation, though this was not initiated as no abnormal conditions were identified post-landing.
Aircraft Systems & Technical Analysis
The Bombardier CRJ-900 is fitted with lavatory smoke detection systems that include photoelectric sensors designed to detect the presence of particulate matter consistent with combustion. These detectors are susceptible to false positives triggered by aerosols, steam, or high humidity under certain conditions.
Following the incident, an inspection of the sensor system was performed. Maintenance engineers reported no physical signs of smoke, fire, or electrical malfunction. The smoke detector in question was removed and quarantined for further analysis by Endeavor’s maintenance quality team.
No foreign objects or malfunctioning devices were found in the lavatory, and the aircraft’s built-in fire suppression system did not deploy. FDR (Flight Data Recorder) data confirmed a brief but isolated activation signal from the lavatory sensor at 15:36, with no follow-up alerts.
The aircraft’s ECS (Environmental Control System) recorded stable temperature and pressure differentials throughout the event, indicating no systemic bleed air or duct contamination that could have caused smoke to enter the cabin.
The root cause of the false activation remains under investigation, with initial findings pointing towards possible environmental contamination or a sensor calibration drift.
Passenger Experience & Cabin Conditions
Passengers seated near the rear of the aircraft reported that cabin crew responded swiftly and professionally to the in-flight alert. Some reported seeing crew members retrieve equipment from storage lockers and move swiftly to the rear lavatory area.
There were no reports of smoke smell, heat, or discomfort within the passenger cabin. No panic or distress was observed among the passengers, and no medical attention was required.
Cabin crew kept passengers informed via the PA system, explaining that a smoke warning had been received and that safety checks were underway. Passengers were told to remain seated with seatbelts fastened until after landing.
Upon landing, the aircraft remained on the remote stand with engines shut down. Passengers were disembarked by airside buses and taken to the terminal.
Emergency Response & Aftermath
Cincinnati/Northern Kentucky Airport Fire and Rescue units met the aircraft on the taxiway. Ground services conducted a full external inspection of the fuselage and aft section but observed no signs of fire or damage.
No runway closures or operational delays occurred as a result of the incident. However, the aircraft was temporarily removed from service pending a maintenance inspection.
The lavatory smoke detector was replaced, and the aircraft underwent a brief operational check flight before being returned to service the following day.
Investigation Status
The FAA was notified of the occurrence and has registered the event as an incident. Endeavor’s in-house safety department has launched a routine internal inquiry under the oversight of Delta Air Lines’ operational safety team.
As no actual smoke or fire was discovered, the event is classified as a false alarm. However, the airline is coordinating with Bombardier and the smoke detector manufacturer to evaluate the sensor’s reliability history and calibration cycle.
No CVR or FDR data retrieval was requested by the NTSB at this time, though Endeavor has preserved the relevant QAR (Quick Access Recorder) data for internal review.
Root Cause & Contributing Factors
As of writing, the preliminary root cause has not been definitively determined. However, early analysis suggests the following contributing factors:
Possible aerosol or environmental vapour (e.g. deodorant or cleaning spray) that may have triggered the sensor Sensor ageing or contamination resulting in false positive activation A transient electrical issue within the detector’s circuit board or power supply
Further component-level investigation is ongoing to determine whether the detector malfunctioned or accurately sensed a short-lived airborne particulate source.
Safety Recommendations & Industry Impact
Although the event did not involve a confirmed fire or smoke, it reinforces the importance of maintaining vigilance during all phases of flight, especially during descent and landing when crew workload is high.
Endeavor Airlines has reminded crews of the need to perform in-flight cabin safety checks with caution when smoke alerts are triggered, even when no immediate signs are present.
The airline’s maintenance department has also begun reviewing the sensor replacement intervals for the lavatory smoke detection systems across its CRJ-900 fleet and may revise internal guidance accordingly.
Bombardier and the equipment manufacturer have been notified, and a technical advisory may follow if similar events are logged by other operators.
Conclusion
The incident aboard Endeavor Airlines flight DL-4985 on 30 April 2025 was managed professionally and in accordance with established procedures. While the smoke alert ultimately proved to be a false positive, the coordinated response by the flight deck, cabin crew, and ground services ensured that passenger safety was never compromised.
The event underscores the value of reliable sensor systems, comprehensive crew training, and robust CRM. Continued investigation into the lavatory smoke detector system’s performance will determine if future procedural or equipment changes are required.
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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