Abnormal Landing Gear: Extending the Unexpected

When your landing gear doesn't extend normally, you face one of aviation's most challenging scenarios. But here's what many pilots don't fully appreciate: the A320/A321's design philosophy prioritizes getting you safely on the ground with whatever gear configuration you can achieve. Understanding how abnormal landing gear situations unfold—and why certain procedures exist—can mean the difference between a controlled emergency landing and a catastrophic outcome.

How Normal Landing Gear Operations Work

Before diving into abnormals, it's crucial to understand what you're working with. The A320/A321 landing gear system operates through two main landing gears that retract inward and a nose gear that retracts forward. The green hydraulic system powers all normal operations, with two control units (LGCIUs) managing the sequence and providing cockpit indications.

The system includes multiple confirmation methods: three green lights on the landing gear panel, green triangles on the WHEEL SD page, and the "LDG GEAR DN" memo. This redundancy exists because gear position verification becomes critical during abnormal situations—you need absolute certainty about what's actually down and locked versus what might only appear to be.

The safety valve that prevents hydraulic supply above 264 kt serves a dual purpose: it protects the system from excessive loads while ensuring that gear extension capability is available when you need it most—during approach speeds.

When Things Go Wrong: Abnormal Gear Scenarios

Abnormal landing gear situations typically fall into three categories: complete hydraulic failure requiring gravity extension, partial gear extension where some gears extend normally while others do not, or gears that extend but do not lock properly. Each scenario demands different considerations and techniques.

Gravity Extension Process: When hydraulic power fails, the manual hand crank becomes your lifeline. Turning it clockwise three times disconnects the landing gear from the green hydraulic system, unlocks all doors and gear, and allows gravity and aerodynamic forces to lower the gear. The key takeaway here is that after gravity extension, the gear doors remain open—this impacts your aerodynamics and approach planning.

Partial Extension Scenarios: These present the most complex decision-making challenges. You might have the main gear down but the nose gear up, one main gear extended while the other remains retracted, or a gear that appears down but isn't properly locked. Each configuration requires specific approach and landing techniques.

Critical Decision Points and Procedures

The fundamental principle governing abnormal gear landings is simple: always attempt to land with whatever gear you have, rather than attempting a gear-up landing, except in a ditching scenario. This philosophy drives every subsequent decision and procedure.

Weight Reduction Strategy: Reducing aircraft weight lowers your touchdown speed, which becomes crucial when landing with abnormal gear configurations. This isn't just about fuel dumping—it’s about physics. Lower touchdown speeds mean less energy to dissipate, reduced structural loads, and more time to maintain control during the landing roll.

Fuel Imbalance Considerations: If you have asymmetric gear extension, creating fuel imbalance to keep the lighter wing (typically the side with retracted gear) elevated longer can delay nacelle contact with the runway. The procedure specifically notes to ignore fuel imbalance advisories because the handling implications are minimal compared to the benefits of delayed ground contact.

System Behavior During Abnormal Operations

Understanding how aircraft systems behave with abnormal gear configurations is essential for proper management. Ground spoilers remain disarmed if one or both main gears aren't properly positioned—this preserves roll control authority when you need it most. The system recognizes that deploying spoilers with asymmetric gear could create uncontrollable rolling moments.

Do not arm the autobrake; instead, rely on manual braking, which provides better control during abnormal landings. You can modulate brake pressure based on the aircraft's behavior rather than relying on a system that can't account for your specific abnormal configuration.

The anti-skid system presents a particular challenge when one main gear isn't extended. The system calculates reference speeds based on wheel speed data, but with asymmetric gear, these calculations become invalid. The procedure calls for turning off anti-skid to prevent continuous brake release commands that would eliminate your stopping capability.

Approach and Landing Techniques

Engine Management Strategy: The timing of engine shutdown becomes critical and varies based on your gear configuration. With abnormal nose gear, shut down engines before nose impact to prevent fuel spillage and fire risk. With one abnormal main gear, shut down at touchdown to maintain control authority until ground contact. With both main gears abnormal, shut down during flare before touchdown—you need to eliminate thrust before the nacelles contact the runway.

This timing strategy balances two competing needs: maintaining control authority as long as possible while preventing fuel system damage and fire risk. Hydraulic power remains available for approximately 30 s after engine shutdown, giving you a brief window of continued flight control effectiveness.

Reverse Thrust Limitations: Avoid using reverse thrust with abnormal main gear, as it can lead to unintended ground spoiler deployment, resulting in asymmetric lift that could destabilize the aircraft. With abnormal nose gear, reverse thrust generates nose-down forces that accelerate nose contact with the runway—precisely what you're trying to delay.

Post-Landing Procedures and Safety Considerations

Once the aircraft stops completely and flight controls are no longer needed, press the engine and APU fire pushbuttons. This immediate action prevents fire risk from fuel system damage that may have occurred during the abnormal landing sequence.

The emphasis on "complete stop" and "flight controls no longer needed" is crucial—you maintain every available control input until the aircraft is fully stopped. Even damaged flight controls might provide some effectiveness during the landing roll.

Runway Foaming: While ATC may offer runway foaming, it's not mandatory. The foam might reduce braking effectiveness on portions of the runway where you have working gear and brakes. The decision should be based on your specific situation and the airport's capabilities.

Understanding the System's Logic

The A320/A321's abnormal landing gear procedures reflect a deep understanding of aircraft behavior and energy management. Every limitation and procedure exists because of specific failure modes and their consequences.

The system's approach to abnormal gear situations prioritizes controllability over convenience. Manual braking over autobrake, anti-skid off rather than unreliable, engine shutdown timing based on gear configuration—each decision maximizes your control authority when you need it most.

This comprehensive understanding of abnormal landing gear operations transforms emergency procedures from memorized steps into logical responses to system behavior. When you understand why each procedure exists and how systems interact during abnormal operations, you're better equipped to handle the unexpected variations that real emergencies often present.

A320 abnormal landing gear in depth – gravity extension, partial deployment scenarios, anti-skid logic, engine shutdown timing, and why each procedure exists.