ABN FLAPS/SLATS: When the High-Lift System Fails

Every time you configure the A320/A321 for takeoff or landing, you rely on a sophisticated system of slats and flaps that transforms your aircraft's wing for different phases of flight. But what happens when this system fails? How do you safely manage an approach when your flaps jam at an unexpected position, or when your slats refuse to extend? Understanding abnormal flaps/slats operations isn't just about following procedures—it's about comprehending how these failures fundamentally change your aircraft's performance and handling characteristics.

How the Normal System Works

The A320/A321's high-lift system operates through two Slat/Flap Control Computers (SFCCs), each managing both slat and flap channels. The system uses hydraulic power from multiple sources: slats rely on green and blue hydraulic systems, while flaps use yellow and green systems. This redundancy means that even with one hydraulic system failure, surfaces can still move, just at half speed.

The flaps lever on your center pedestal controls five preset configurations, from clean (0 °/0 °) through full landing configuration. Each position represents an optimized combination of slat and flap angles designed for specific flight phases. The system includes multiple safety features: Wing Tip Brakes (WTBs) that lock surfaces during uncommanded movements, asymmetry detection that prevents dangerous wing-to-wing differences, and disconnect detection that stops flap operation if attachment failures occur.

When Things Go Wrong: Understanding ABN FLAPS/SLATS

Abnormal flaps/slats conditions typically result from three primary causes: double SFCC failure, double hydraulic system failure (particularly B + G or Y + G combinations), or jammed surfaces due to wing tip brake activation. Each scenario creates a different operational challenge, but all share common consequences that fundamentally alter your aircraft's performance envelope.

The immediate impact affects multiple systems simultaneously. Your flight control laws may degrade, requiring different approach attitudes and techniques. Approach speeds increase significantly, extending your landing distances. Go-around procedures become more complex, and your FMS predictions for fuel consumption and speeds become unreliable due to the aircraft's altered aerodynamic characteristics.

Managing the Failure During Different Flight Phases

Failure at takeoff presents unique challenges. The key is using the speed knob to manually select appropriate speeds, preventing VFE exceedance during the critical phase when flaps or slats should be retracting. Your next actions depend entirely on available landing distance and aircraft weight—factors determining whether you can safely return to your departure airport or must continue to a more suitable destination.

Failure during the approach typically becomes apparent when you move the flap lever during your normal configuration sequence. If A/THR is active, the managed speed target automatically adjusts to the next maneuvering speed (such as S speed when the flap lever is set to position 1). However, this may not be appropriate for your actual surface position.

Critical Speed and Configuration Management

The cornerstone of managing abnormal flaps/slats is understanding the (e)QRH guideline: "SPD SEL............VFE NEXT -5 kt." This isn't just a number—it's your safety margin that prevents structural damage while allowing continued safe flight. You can reduce speed below your current configuration's maneuvering speed, but you must stay above VLS (Lowest Selectable Speed).

Perform all speed reductions and configuration changes with wings level whenever possible. This reduces stress on the aircraft structure and provides better control during these critical phases. Set VAPP close to VLS plus wind correction, based on your actual slat/flap position—not the lever position. Importantly, VAPP may actually be lower than VLS in some abnormal configurations.

Approach and Landing Considerations

The autopilot can remain engaged down to 500 ft AGL, but requires close monitoring due to potentially suboptimal performance in abnormal configurations. Your arrival briefing must highlight the increased risk of tail strike during landing—the altered aerodynamics and potentially higher approach speeds create conditions where this risk significantly increases.

Go-around procedures require special attention. Review your standard go-around configuration and ensure all callouts are performed correctly. During the missed approach phase, use selected speed to manage acceleration until reaching the required configuration speed. The standard acceleration altitude procedures may not apply normally due to your aircraft's altered performance characteristics.

Diversion Planning and Fuel Considerations

When diverting with jammed flaps or slats, account for dramatically increased fuel consumption. The extended surfaces create additional drag throughout your flight, requiring careful fuel planning to ensure adequate reserves. If flaps or slats remain extended during diversion, you're limited to a maximum cruise altitude of 20 000 feet—a significant operational constraint that affects both fuel efficiency and routing options.

Operational Implications and Decision Making

Understanding abnormal flaps/slats goes beyond following procedures—it's about recognizing how these failures change your aircraft's fundamental characteristics. The increased approach speeds aren't just numbers to memorize; they reflect the wing's altered lift characteristics. The longer landing distances result from both higher approach speeds and potentially reduced braking effectiveness due to altered aerodynamics.

The preference for an early stabilized approach becomes critical. With degraded systems and altered performance, you need more time to assess and adjust your approach parameters. The normal last-minute configuration changes that might be acceptable in normal operations become potentially dangerous with abnormal flaps/slats.

Your FMS predictions become unreliable because the system's performance calculations are based on normal aerodynamic data. This means increased pilot workload for manual calculations and conservative fuel planning. The cascading effects of a flaps/slats failure extend far beyond the immediate system—they impact your entire flight management strategy.

Conclusion: Building Operational Understanding

Abnormal flaps/slats procedures represent one of the more complex failure scenarios you'll encounter, requiring integration of systems knowledge, performance understanding, and operational judgment. The key is recognizing that these failures don't just change numbers—they change how your aircraft flies, how it responds to control inputs, and how you must manage energy throughout the approach and landing phases.

Success in managing these situations comes from understanding the underlying aerodynamics and system interactions, not just memorizing procedures. When your high-lift system fails, you're not just following a checklist—you're managing a fundamentally different aircraft that requires adapted techniques, conservative planning, and heightened awareness of the changed operational envelope.

What changes when the A320 high-lift system fails – altered speeds, degraded flight control laws, approach technique, and go-around considerations with jammed surfaces.