In the dynamic environment of flight simulation training, few events demand as rapid and precise a response as a flap or slat malfunction during the approach phase. These high‑lift devices are critical for generating the additional lift required at low speeds, and any abnormal behavior can dramatically alter aircraft handling, performance margins, and landing distance. Mastering the management of such malfunctions in the simulator builds the procedural discipline, systems knowledge, and decision‑making skills that translate directly to real‑world safety. This article provides an expanded, in‑depth guide to understanding, recognizing, and managing unusual flap or slat malfunctions during approach in simulations—from aerodynamic fundamentals to advanced crew coordination techniques.

The Aerodynamic Role of Flaps and Slats

To appreciate why a flap or slat malfunction is so significant, one must first understand their purpose. Flaps are hinged panels on the trailing edge of the wing, and slats are movable surfaces on the leading edge. Both devices alter the wing’s camber and, in the case of slats, also delay airflow separation at high angles of attack. This combination increases the maximum lift coefficient, allowing the aircraft to fly at lower speeds without stalling—essential for safely slowing down on approach and achieving short landing distances.

When flaps extend, they increase both lift and drag. The pilot selects incremental settings (e.g., Flaps 1, 2, 3, Full) depending on the approach speed and configuration requirements. Slats typically deploy automatically or in coordination with the flap lever. The specific schedule varies by aircraft type; for example, on the Boeing 737, the leading‑edge slats extend fully when the flap lever reaches position 1, while the trailing‑edge flaps move in steps. On the Airbus A320, the system is even more integrated, with slats and flaps moving symmetrically in response to the “Flaps” lever.

Any deviation from the normal extension schedule—asymmetric deployment, partial extension, failure to retract, or uncommanded movement—destroys the carefully balanced aerodynamic configuration. Asymmetric flaps create a rolling moment that must be countered with control inputs, increasing pilot workload and potentially exceeding the control authority if uncorrected. Partial or complete failure to deploy may result in a higher‑than‑normal approach speed, longer landing distance, and reduced stall margin. Understanding these effects is the first step toward managing them in the simulator.

Common Types of Flap and Slat Malfunctions in Simulations

Simulation instructors can introduce a wide variety of flap and slat failures. The most common ones fall into several categories:

Asymmetric Deployment

One wing’s flaps or slats extend or retract at a different rate or position than the other. This can be caused by a mechanical jam, hydraulic system failure, or control cable issue. In the simulator, asymmetric failures are typically modeled with a graduated severity—from a slight position difference to a full lock on one side.

Partial Deployment or In‑Transit Jam

The flap or slat system stops moving partway between settings. For example, the flaps may jam at Flaps 10 instead of moving to Flaps 20. This results in a configuration that is not included in the normal landing performance tables, requiring the pilot to compute a revised approach speed and landing distance.

Complete Failure to Deploy

When the pilot selects a lower flap setting, the surfaces remain retracted. This is often associated with a hydraulic, electrical, or mechanical system failure. The aircraft will have a higher stall speed and need a faster approach, increasing runway length requirements and reducing visibility over the nose in some types.

Uncommanded Retraction or Extension

A sudden change in flap or slat position without pilot input can be startling. This scenario trains pilots to quickly recognize the change, maintain aircraft control, and use the appropriate emergency procedures—often including deployment of the alternate or manual extension system.

Slat Failure Only

Slats may fail to extend while flaps deploy normally, or vice versa. Because slats are essential for high‑angle‑of‑attack lift, a missing slat can significantly reduce the stall margin. In the simulator, this forces the pilot to fly a faster final approach and to avoid aggressive pitch inputs.

Each type of malfunction presents distinct handling and procedural challenges. The simulator environment allows pilots to practice recognition and response without risk, building the mental models needed to react calmly in real‑world situations.

Managing the Malfunction: A Structured Approach

When a flap or slat malfunction occurs during the approach phase, time is limited. A structured response—based on the operator’s standard operating procedures (SOPs), the flight manual, and crew resource management (CRM)—is essential. The following step‑by‑step framework is widely taught in modern airline training programmes:

1. Maintain Aircraft Control

The immediate priority is to fly the airplane. Simulator instructors stress that pilots must keep the aircraft in a safe flight path and attitude, especially if the malfunction causes an unexpected roll or pitch change. Use trim and control inputs to maintain wings‑level and a stable descent profile, even if the approach configuration is abnormal.

2. Identify the Failure

Scan the flap/slat indication on the flight deck: on a Boeing aircraft, the trailing‑edge flap position indicator and the leading‑edge slat indication lights; on an Airbus, the ECAM (Electronic Centralised Aircraft Monitor) or FWS (Flight Warning System) display. Note any asymmetry, position disagreement, or failure messages. Cross‑reference with the primary flight display (PFD) for unusual attitude indications.

3. Apply the Memory Items and Immediate Actions

Many operator checklists include a memory item for asymmetric flaps/slats: typically “Flap/ slat asymmetry – retract flaps to zero, then select the next detent below the jam position, if possible.” Other memory items may include disconnecting the autopilot to allow direct manual control, or moving the flap lever to a position that reduces the asymmetry. The specific steps depend on the aircraft type and should be drilled in the simulator until they become reflexive.

For example, the Boeing 737 Quick Reference Handbook (QRH) for “Flap Asymmetry” directs the pilot to retract the flaps to zero, then re‑select an intermediate setting. If the asymmetry persists, they continue with the non‑normal landing procedure using the existing flap position. In the Airbus A320, the ECAM procedure guides the crew through the required steps, which may include selecting the alternate flap/slat control system.

4. Configure for Landing

Once the immediate actions are complete, the crew must decide on the final landing configuration. Options include:

  • Landing with the flaps/slats in their current (possibly asymmetrical) position if control can be maintained and performance permits.
  • Selecting an alternate extension method (e.g., manual crank or alternate hydraulic system) if available and time allows.
  • Landing with flaps retracted entirely if the asymmetric condition cannot be corrected, using a higher approach speed (typically VREF + 20–30 knots).

In the simulator, pilots learn to quickly calculate the appropriate landing reference speed using the non‑normal performance tables or the flight management system. They also compute the required landing distance for the configuration, accounting for the higher speed and reduced braking effectiveness.

5. Communicate and Coordinate

Inform air traffic control (ATC) of the malfunction and the intended plan. In the simulator, this teaches pilots to manage the radio workload while flying an abnormal approach. It also allows ATC to provide priority handling, additional spacing, or runway selection with better lighting and length. Within the cockpit, the pilot flying (PF) and pilot monitoring (PM) must coordinate clearly: the PM reads checklists, cross‑checks speeds, and handles secondary tasks while the PF maintains aircraft control and flies the approach.

6. Prepare for a Go‑Around

Even with a well‑handled flap/slat malfunction, a go‑around may be necessary if the approach becomes unstable or if the landing cannot be assured with safety margins. Simulator training emphasises that go‑around procedures remain valid even with abnormal flap settings—the aircraft will still climb, though with a reduced climb gradient and higher drag. Pilots must be ready to apply go‑around thrust, rotate to the appropriate pitch attitude, and reconfigure the flaps to a suitable setting (usually retracting to the go‑around flap setting if possible).

Simulation Fidelity and Realism

The effectiveness of training for flap/slat malfunctions depends heavily on the fidelity of the simulation. Modern full‑flight simulators (Level D) accurately model the aerodynamic changes caused by asymmetric or partially deployed flaps, including the induced roll, changes in stall speed, and altered pitch response. In the best simulators, the motion system can even reproduce the subtle vibrations or hydraulic feedback that a real malfunction might generate.

Instructors can programme failures at specific points in the approach, such as when the aircraft is established on the glide path, just before reaching the runway threshold, or during a go‑around. Repetition across multiple scenarios—different airports, weather conditions, aircraft weights—builds the pilot’s ability to generalise the skills. Some operators use “line‑oriented flight training” (LOFT) scenarios where the malfunction is introduced without warning, forcing the crew to manage both the technical and human factors challenges in a realistic context.

Evaluating performance in the simulator also includes assessment of CRM behaviours. The most skilled technical response is worthless if the crew fails to communicate or if one pilot becomes overloaded. Therefore, training sessions should debrief not only the procedural correctness but also the effectiveness of decision‑making, workload distribution, and assertiveness.

Real‑World Lessons from Flap/Slat Incidents

Studying actual incidents reinforces why simulator training is vital. For example, in 1991 a McDonnell Douglas MD‑80 experienced a slat asymmetry during approach to Los Angeles. The crew managed to land safely by following the non‑normal checklist, but the subsequent investigation highlighted the importance of immediate recognition and use of the correct procedure. In 2018, an Airbus A320 in Europe had a flap asymmetry that required the crew to use the alternate extension system and land at a higher speed; simulator‑trained crews were able to handle the situation routinely.

Another well‑known case involved a Boeing 737 that suffered a leading‑edge slat failure on approach. The flight crew had practiced exactly that scenario in the simulator only weeks earlier, allowing them to respond smoothly and land without incident. These stories underscore the value of realistic, recurrent simulator training for rare but critical failures.

Beyond Single‑Failure Scenarios: Compound Malfunctions

Advanced simulation sessions can introduce compound malfunctions—for instance, a flap asymmetry combined with an engine failure on approach, or a slat failure coupled with a hydraulic leak that limits manual extension options. These scenarios push pilots to prioritise tasks, manage multiple checklists, and make trade‑offs under time pressure. Training for such compound events builds resilience and prevents over‑reliance on any single system.

In these exercises, the instructor may also inject distractions: ATC changing runways, a medical emergency in the cabin, or an inadvertent altitude deviation. The goal is to simulate the real‑world chaos that can accompany an abnormal situation, preparing pilots to maintain structured decision‑making even when the environment is challenging.

Integrating Flap/Slat Malfunction Training into a Recurrent Programme

A robust recurring training programme should include flap/slat malfunctions as a standard item. The European Union Aviation Safety Agency (EASA) and the U.S. Federal Aviation Administration (FAA) both require operators to conduct non‑normal procedures training in simulators, with specific emphasis on flight control system failures. Many operators schedule at least one session per year focused on high‑lift device malfunctions.

Training should cover both low‑time first officers and experienced captains. Each crew member benefits from practising the failure from both seats—handling the controls or managing the checklists. Cross‑training also helps junior pilots gain confidence in calling out deviations and challenging assumptions, which is critical for safety culture.

Additionally, instructors should tailor the complexity to the fleet type. For an aircraft with a manual flap extension system (e.g., older Boeing 737 models), the training must include physical aspects like turning the manual cranking handle. For an Airbus A380 with fully electronic control, the focus shifts to understanding the alternate law protections and the ECAM logic.

The Role of Procedural Knowledge and Mental Models

Mastering flap/slat malfunction procedures is not just about memorising steps; it is about building a deep mental model of the aircraft’s systems and performance limits. Simulator training should encourage pilots to ask “why” behind each action. Why does the QRH say to retract flaps first? Why is the minimum drag configuration often with flaps partially extended? Understanding these principles allows pilots to adapt when the checklist does not perfectly match the situation—for example, when the failure occurs at an extremely low altitude where any configuration change could be destabilising.

Many airlines use threat and error management (TEM) frameworks to help pilots recognise the “threat” of a malfunction, mitigate errors, and use available resources. In flap/slat scenarios, common threats include high workload, time pressure, and distraction. Training should explicitly address these human factors, such as providing briefings that set up expectations for possible failures, using standard call‑outs, and practising workload‑shedding—the art of delaying non‑essential tasks.

Take‑Home Points for Simulator Training

To summarise the key elements that make flap/slat malfunction training effective:

  • Recognise early: The first sign may be a roll, an ECAM message, or a flap position light anomaly. Train pilots to scan during the approach checklist.
  • Fly the aircraft first: No checklist is more important than maintaining control. Use automation wisely—autopilot can be left on if it can handle the asymmetry, but be ready to disconnect.
  • Follow the procedure: Use the applicable QRH/ECAM/FCOM procedure step‑by‑step. Do not skip or guess.
  • Compute performance: Determine the correct approach speed, landing distance, and go‑around climb gradient for the actual configuration.
  • Communicate: Brief the crew and ATC clearly. Use standard phraseology.
  • Be ready to go around: If any doubt exists about a stabilised landing, execute a go‑around.
  • Debrief thoroughly: After the simulation, analyse what went well and what could be improved—both technically and in terms of CRM.

Conclusion

Managing unusual flap or slat malfunctions during approach is one of the most demanding abnormal situations a pilot can face. The aerodynamic changes, performance effects, and procedural complexity require a well‑trained crew that can act quickly and decisively. Flight simulation provides the ideal environment for building these skills, allowing pilots to experience a wide range of failures in a realistic but risk‑free setting.

By combining thorough systems knowledge, standardised procedures, and strong CRM, pilots can safely land the aircraft even with a degraded high‑lift system. Continuous practice in the simulator—reinforced by feedback and scenario variation—ensures that when a real malfunction occurs, the response is automatic and confident. Ultimately, this training contributes directly to the high level of safety enjoyed in modern aviation.

For further reading on flap and slat systems and related training, refer to the following resources: