Flight AA-4601 | Registration: N855RW
Date: 6 April 2025 | Location: En Route to Portland, Diverted to Boston Logan (KBOS), USA
Flight Details
• Aircraft Type: Embraer ERJ-170-100 (E170)
• Engines: 2 × General Electric CF34-8E5
• Operator: Republic Airways, operating on behalf of American Airlines
• Registration: N855RW
• Flight Number: AA-4601
• Callsign: RPA4601
• Route: New York LaGuardia (KLGA) to Portland International Jetport (KPWM), USA
• Date of Incident: 6 April 2025
• Total Occupants: 76 (70 passengers, 6 crew)
• Weather Conditions: VMC in Boston, light wind, no precipitation reported
Introduction
On 6 April 2025, a Republic Airways Embraer E170 operating for American Airlines as flight AA-4601 diverted to Boston Logan Airport following a flap system malfunction during approach to Portland, Maine. The aircraft, registration N855RW, was descending through 11,000 feet when the crew aborted their approach due to flap deployment issues, requiring a landing at a higher than normal speed. The aircraft landed safely on runway 33L at Boston approximately 35 minutes after the decision to divert. There were no injuries.
Sequence of Events
AA-4601 departed LaGuardia Airport in the evening and was on final approach into Portland when the crew encountered a flap malfunction. At approximately 11,000 feet, flap extension issues were detected—likely through abnormal flap asymmetry alerts or mechanical resistance during the approach configuration phase.
Recognising the aircraft would be unable to configure for a normal landing due to restricted flap extension, the flight crew elected to discontinue the approach to Portland. Instead, they coordinated with ATC for a diversion to Boston Logan International Airport, which offered a longer runway better suited for a higher-speed landing profile.
The flight proceeded directly to Boston, where it entered a brief holding pattern to prepare for landing. The crew conducted a flapless or partially configured landing at an elevated Vref (reference landing speed) and landed safely on runway 33L without the need for emergency services.
Crew & Communication
The flight crew promptly identified the flap malfunction and discontinued descent in accordance with Embraer’s abnormal procedures. Communications with air traffic control were precise and professional. The crew advised of the mechanical issue and requested diversion, citing the requirement for a longer runway due to limited flap extension.
While the aircraft did not declare an emergency (MAYDAY), it is understood a precautionary alert and request for priority handling were submitted. ATC facilitated a direct routing to Boston, and the flight was prioritised for approach and landing sequencing.
Cabin crew were briefed by the flight deck and subsequently informed passengers of the diversion. The situation remained calm onboard, and the aircraft touched down without incident.
Aircraft Systems & Technical Analysis
The ERJ-170 series features a fly-by-wire flight control system with electronically actuated trailing edge flaps. Flap deployment is monitored and controlled through:
• Flap Electronic Control Unit (FECU)
• Position sensors and feedback potentiometers
• Asymmetry protection and flap motor controllers
Common causes of flap malfunctions include:
• Jammed flap track or actuator
• Asymmetry between left and right flap assemblies
• Hydraulic fluid pressure loss or actuator motor failure
• Faulty position sensors sending erroneous signals
• FECU or wiring faults
In this case, the inability to deploy flaps to the intended landing setting required the crew to execute a higher-speed approach. Based on standard E170 flap failure procedures, landing speeds could increase from approximately 125 knots to 145–155 knots depending on the final flap position achieved.
Post-flight maintenance would include:
• FECU diagnostic download
• Flap track and actuator inspection
• Verification of asymmetry sensors
• Review of any existing deferred maintenance items related to flight controls
The fact that the aircraft was not returned to Portland or resumed its original routing suggests the fault was not resettable inflight.
Passenger Experience & Cabin Conditions
There were no reports of discomfort or adverse cabin events during the flight. Passengers may have noticed the abnormal descent profile or been informed of the situation via cabin announcements. Cabin crew maintained routine service until the descent phase, where a short briefing may have been issued to prepare passengers for an alternate landing location.
Passengers were re-accommodated via ground transportation or alternate flights from Boston. No injuries, oxygen deployment, or onboard disruption occurred.
Emergency Response & Aftermath
Emergency services at Boston Logan were placed on standby but not activated, given the nature of the malfunction and controlled landing. The aircraft vacated the runway normally and taxied under its own power to a designated gate or hard stand.
Republic Airways engineering staff at Boston initiated fault tracing immediately after shutdown. The aircraft was removed from service for repairs and inspection.
The FAA confirmed the event and announced it would investigate the mechanical issue as part of routine post-incident oversight.
Investigation Status
The Federal Aviation Administration (FAA) has acknowledged the incident and will conduct a standard review. As there were no injuries or declared emergency, this is not considered a serious incident under NTSB criteria.
The investigation will focus on:
• The cause of the flap malfunction
• Whether the issue was known or deferred prior to departure
• The effectiveness of the crew’s response and adherence to abnormal procedures
• Whether design or maintenance flaws contributed
Data from the FDR and maintenance logs will be instrumental in confirming the failure mechanism.
Root Cause & Contributing Factors
The flap malfunction may have resulted from:
• Mechanical jamming in the flap track system
• Asymmetry detection triggering protection mode
• Electrical or hydraulic actuator failure
• Control unit or software anomaly preventing commanded extension
Contributing factors could include:
• Previous wear or unreported binding in the flap system
• Recent maintenance not detecting early signs of failure
• Environmental effects such as icing, debris, or hydraulic contamination
Until inspection reports are complete, the exact fault remains undetermined.
Safety Recommendations & Industry Impact
While minor in outcome, the event supports broader safety observations:
• The importance of flap system redundancy and fault tolerance
• The value of multiple landing site options near approach paths
• The necessity of thorough flap system inspections on ageing regional aircraft
• Continued emphasis on crew simulator training for high-speed landings due to configuration failures
If component-specific failures are confirmed, Republic Airways may issue internal bulletins, and Embraer could consider service advisories or maintenance check updates.
Conclusion
The diversion of Republic Airways flight AA-4601 to Boston due to a flap system malfunction was managed professionally and without injury or damage. The flight crew’s decision to reroute to an airport with a longer runway and their safe execution of a higher-speed approach reflects sound judgement and strong procedural adherence.
This incident serves as a reminder of the complexity of flap systems and the critical role they play in approach configuration—particularly on regional aircraft operating into shorter or weather-sensitive destinations like Portland.
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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