Flight Details
Aircraft Type: Boeing 737-800
Operator: KLM Royal Dutch Airlines
Registration: PH-BXN
Flight Number: KL1511
Route: Amsterdam Schiphol (EHAM) to Barcelona El Prat (LEBL)
Date of Incident: 28 April 2025
Total Occupants: Not disclosed (typical B738 capacity ~189)
Weather Conditions: VMC, light surface winds reported
Introduction
On 28 April 2025, a KLM Royal Dutch Airlines Boeing 737-800 aircraft operating as flight KL1511 from Amsterdam to Barcelona encountered an in-flight technical malfunction involving the aircraft’s trailing edge flaps shortly after departure. This marked the second flap-related anomaly involving the same aircraft, registration PH-BXN, within 24 hours.
Shortly after climbing out of runway 36L at Amsterdam Schiphol, the flight crew levelled off at 10,000 feet after receiving an indication of an abnormal flap condition. The crew entered a series of holding patterns while executing the Quick Reference Handbook (QRH) checklists before electing to return to Amsterdam for a precautionary landing. The aircraft touched down safely on runway 36R approximately one hour after departure. No injuries were reported.
Sequence of Events
KL1511 departed Schiphol during the mid-morning wave of outbound European services. Shortly after takeoff, with flaps likely in retraction phase from takeoff configuration, the crew received abnormal flap indications via the aircraft’s EICAS or associated annunciators. It is common procedure to discontinue further climb if the flap/slat configuration is uncertain or malfunctioning, as flap extension at high speeds can lead to severe aerodynamic stress or asymmetry.
The aircraft levelled at FL100, where speeds are more manageable and air density permits greater control margins in abnormal configurations. Amsterdam Radar coordinated vectors for the aircraft to remain in a series of right-hand holding patterns while the crew worked the applicable QRH flows.
During this time, the Captain and First Officer would have reviewed:
Flap position indicators. Any “FLAP DISAGREE” or “LE FLAPS TRANSIT” cautions. Fuel burn estimates for return landing weight. Configuration limitations (e.g., VFE, Vref with partial flaps).
With resolution not forthcoming and redundancy limits reached, the crew initiated a return to base. ATC cleared the aircraft for an approach to runway 36R, which offers longer length and full RESA (Runway End Safety Area) margins for potential abnormal landings. The aircraft landed without incident and taxied to stand under its own power.
Crew and Communication
The cockpit crew followed manufacturer and operator protocols, with no Mayday or PAN declared, indicating that the aircraft remained fully controllable. ATC recordings confirmed calm and clear communication, with controllers offering discretionary headings and descent profiles to suit the crew’s operational tempo.
CRM between flight crew appeared coordinated, and cabin crew would have been informed to prepare for a precautionary return. No evacuation was required on landing.
The ground controller directed the aircraft to a remote stand, where engineers from KLM Engineering & Maintenance initiated technical diagnostics.
Technical Overview: Flap System Mechanics
The Boeing 737-800 flap system is hydraulically actuated and electrically controlled, using a series of tracks and carriages extending from the wing trailing edge. The system allows flap settings from 1 to 40, with intermediate detents used during approach and landing phases. Any discrepancy between commanded and actual flap positions triggers a caution, while asymmetry will trigger lockout protocols.
Potential causes of flap issues include:
Asymmetric flap extension. Failed actuator or cracked track. Electrical signal interruption in the Flap Control Unit (FCU). Sensor error leading to false caution.
Given that the same aircraft had returned to Amsterdam the day before—on 27 April—for an identical issue, this second return points towards a persistent or intermittently recurring defect.
The aircraft remained on the ground for approximately 50 hours following the second incident, underwent a test flight, and returned again to ground status. This suggests that maintenance engineers were either unable to duplicate the fault reliably or that the system required part replacement and further troubleshooting.
Passenger Experience and Cabin Conditions
No abnormal conditions in the cabin were reported. Passengers were likely briefed during the holding period and descent regarding the precautionary return. KLM’s ground operations would have facilitated passenger reaccommodation or rebooking.
A replacement Boeing 737-800, registration PH-BXY, was dispatched and reached Barcelona with a delay of approximately three hours.
Emergency Response and Aftermath
No airport emergency response was activated beyond standard precautionary readiness. Runway 36R was temporarily assigned priority arrival status but returned to regular use shortly after the aircraft’s safe touchdown.
The aircraft was towed to a maintenance bay, where engineers conducted CMC (Central Maintenance Computer) fault code downloads and physical inspection of the flap tracks, motors, and control relays.
The aircraft’s maintenance logs likely included flap-related deferred items or recent component replacements. As the same airframe had returned the previous day with an identical fault, investigators would be scrutinising:
Serial numbers of actuators and sensors. Wiring harness continuity. Flight data recorder (FDR) correlation with pilot inputs. Airworthiness Directive (AD) compliance for known B738 flap issues.
Investigation Status
No formal investigation has been launched by the Dutch Safety Board (OVV), as this incident did not involve injuries or a significant failure. However, it is likely to be documented within the airline’s Safety Management System (SMS) for trend monitoring and reliability tracking.
If the same flap component or system controller is implicated in both occurrences, KLM may issue a fleet-wide maintenance notice or inspect similarly aged aircraft for latent issues.
Root Cause and Contributing Factors
While the final root cause has not been publicly confirmed, several plausible technical triggers exist:
Persistent flap track misalignment causing asymmetry lockout. Faulty flap position sensor falsely flagging system disagree. Control unit intermittency due to temperature or electrical noise. Hydraulics delivering inconsistent actuator pressure to one side.
A contributing factor may have been an incomplete fix from the 27 April return. If the system passed post-incident testing but failed under load during the next flight, the underlying issue could be an intermittent short or progressive mechanical wear not evident during ground tests.
The aircraft’s extended downtime and subsequent test flight suggest that KLM maintenance took comprehensive action beyond superficial inspection.
Safety Recommendations and Industry Implications
This event reiterates the importance of:
Caution when clearing aircraft for service after intermittent faults. Enhanced post-return test flight protocols. Early flagging of repeated systems issues in SMS databases. Maintaining updated spares inventory for critical flight control actuators.
Boeing and KLM may also review service bulletins or consider software updates for the Flap Control Unit if repeat faults are detected across the fleet.
Conclusion
KLM flight KL1511 returned to Amsterdam after a flap system anomaly was detected at FL100, marking the second such occurrence for airframe PH-BXN within 24 hours. The incident was handled professionally and without risk escalation. While no injuries occurred, the repeat nature of the failure warrants attention within KLM’s engineering review board and may prompt further fleetwide technical checks.
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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