Taxiing – Aircraft Movement on Ground Under Own Power

Definition of Taxiing

Taxiing is the controlled ground movement of an aircraft under its own power, excluding flight and towing operations. Used both before takeoff and after landing, taxiing allows aircraft to move between runways, aprons, hangars, and other airport facilities. This process is fundamental for transitioning between the runway and terminal or maintenance areas and must comply with strict safety, operational, and procedural requirements set by global aviation authorities.

Both the FAA (Federal Aviation Administration) and ICAO (International Civil Aviation Organization) define taxiing as movement under the aircraft’s own propulsion on the aerodrome surface. This excludes movement by pushback or tow vehicles. While most commonly associated with fixed-wing aircraft, helicopters with wheels also taxi, and rotorcraft may use hover or air taxi modes for ground movement.

Taxiing is a critical phase of flight operations, requiring careful adherence to procedures, situational awareness, and coordination with Air Traffic Control (ATC). Surface conditions, airport layout, and traffic density all influence the complexity and risk associated with taxiing.

Regulatory and Technical Distinctions

FAA Definition

The FAA defines taxiing as the movement of an airplane under its own power on the surface of an airport, excluding towing. Pilots must receive explicit ATC clearance at controlled airports before taxiing, ensuring coordination and safety. Taxiing includes all self-powered movement on paved or unpaved surfaces within the airport, except on active runways unless specifically cleared.

FAA regulations stress maintaining slow, controlled speeds, using checklists, visually scanning for obstacles, and adapting to conditions like poor weather or low visibility. These requirements are designed to minimize runway incursions, surface conflicts, and accidents.

ICAO and Eurocontrol Definitions

The ICAO definition closely mirrors the FAA’s, emphasizing self-powered ground movement before takeoff or after landing. ICAO standards, found in Annex 14 to the Convention on International Civil Aviation, are adopted worldwide to harmonize taxiing procedures.

Eurocontrol, which oversees air navigation in Europe, includes pushback in “taxi-out time” for statistical tracking, though operationally, taxiing is still considered self-powered movement. This distinction helps airports and airlines measure turnaround times and delay causes, but does not alter the pilot’s responsibilities or safety requirements.

Pushback vs. Taxiing

Pushback is the process of moving an aircraft backward from a gate using a ground vehicle (tug). Since most commercial jets cannot reverse under their own power due to safety and FOD (Foreign Object Damage) risks, pushback is required in many airport settings. Taxiing officially begins once the aircraft moves forward under its own power after disconnection from the tug.

Distinguishing between pushback and taxiing is essential for operational safety. The transition requires clear communication among pilots, ground staff, and ATC to prevent collisions or unauthorized movements.

Helicopter Taxiing Modes

Helicopters may taxi in several ways depending on their configuration and operational needs:

• Ground Taxi: Wheeled helicopters move along taxiways like airplanes using engine or rotor power.
• Hover Taxi: The helicopter hovers a few feet above the ground and moves slowly, typically used to avoid obstacles or operate on rough surfaces.
• Air Taxi: The helicopter moves at a higher hover (up to 100 feet AGL) at faster speeds, useful for obstacle clearance or when ground taxiing is impractical.

Each mode requires specific control techniques and coordination with ATC, especially at busy airports with mixed traffic.

Operational Context: Where and Why Aircraft Taxi

Aerodrome Layout: Taxiways and Aprons

Airports are designed with distinct areas to facilitate safe aircraft movement:

• Aprons (Ramps): Locations for parking, boarding, refueling, and cargo handling, typically adjacent to terminals.
• Taxiways: Marked routes linking aprons, runways, and hangars, identified by yellow centerlines and letter/number designations (e.g., Taxiway A, B1).
• Runways: Used exclusively for takeoff and landing. Taxiing on runways requires explicit ATC clearance.
• Hangars/Maintenance Areas: Accessed via dedicated taxi routes, often with added safety measures.

Purpose of Taxiing

• Pre-Takeoff: Aircraft taxi from gate or parking to the runway threshold after pushback, positioning for departure.
• Post-Landing: After exiting the runway, aircraft taxi to gates, stands, or hangars for unloading, boarding, or maintenance.
• Repositioning: Movement between different airport areas for operational needs.
• Runway/Apron Efficiency: Efficient taxiing clears runways for other traffic and optimizes airport capacity.

Efficient taxiing minimizes delays, reduces fuel consumption, and improves overall airport operations.

Taxiing Procedures

Preparation and Pre-Taxi Checklist

Proper preparation is essential for safety and efficiency:

• ATC Clearance: Pilots obtain explicit clearance before taxiing, which includes the assigned route and any holding instructions.
• Route Review: Pilots study assigned taxiways and potential hotspots to avoid wrong turns or runway incursions.
• Airport Diagram: Reference diagrams help anticipate turns and areas of congestion.
• Visual Scan: Pilots check for obstacles, vehicles, and personnel before movement.
• Brake/Engine Check: Brakes are tested, and engine power is applied gradually.
• Flight Control Check: All controls are checked for proper movement and response.

A thorough pre-taxi checklist ensures the aircraft is ready for safe ground movement.

Initiating Taxi

Taxiing is initiated by:

1. Releasing Brakes: Parking brake is disengaged.
2. Applying Throttle: Engine power is gently increased to start movement.
3. Monitoring Acceleration: Speed is moderated as soon as the aircraft starts moving.
4. Directional Control: Steering is managed via nosewheel, tailwheel, or tiller.
5. Brake Test: Brakes are tested immediately after rolling.

Smooth initiation avoids mechanical stress and ensures safe movement.

Direction and Speed Control

• Steering: Nosewheel or tailwheel is controlled via rudder pedals or, in large jets, a tiller for tighter turns.
• Speed Management: Taxi speed varies by location and conditions—typically 20–30 knots on main taxiways, 5–10 knots near ramps.
• Braking: Brakes are used sparingly to prevent overheating and wear; throttle is used to regulate speed.
• Instrument Monitoring: Pilots cross-check heading indicators and turn coordinators during taxi.

Typical Taxi Speeds Table:

Turning and Stopping

• Turning: Initiated via rudder pedals or tiller. Differential braking may help in tight turns.
• Sharp Turns: Performed slowly to prevent stress on gear and tires; wing walkers or marshallers may assist.
• Stopping: Throttle to idle, brakes applied smoothly; parking brake set if stationary for a period.
• Instrument Checks: Pilots verify instruments respond as expected during turns.

Taxiing in Various Ground and Wind Conditions

• Wind: Pilots adjust ailerons and elevators to compensate for headwinds, tailwinds, and crosswinds.
• Surface: Extra caution is used on soft, icy, or uneven surfaces; taxi speed is minimized.
• Obstructed/Congested Areas: Vigilance is increased, and ground crew assistance may be required.

Parking and Shutdown

Upon reaching the parking area:

• Positioning: Aircraft are aligned with parking lines, ideally facing into the wind.
• Braking: Aircraft is brought to a complete stop and the parking brake is set.
• Shutdown: Engines are secured, systems powered down, and ground equipment positioned as needed.

Safety Considerations and Best Practices

Avoiding Runway Incursions

• Always read back and confirm taxi clearances with ATC.
• Use airport diagrams and identify hotspots.
• Maintain situational awareness and watch for other traffic.

Night and Low Visibility Taxi

• Use appropriate lights (taxi, landing, navigation).
• Proceed at reduced speeds.
• Rely on ground markings, signage, and instruments.

Environmental and Human Factors

• Monitor for surface contamination (ice, FOD).
• Stay alert to fatigue, distractions, and communication errors.

Taxiing and Airport Efficiency

Taxiing efficiency impacts:

• Airline schedules and on-time performance
• Fuel consumption and emissions
• Runway and gate utilization
• Passenger experience

Advanced surface movement guidance systems, real-time ATC coordination, and airport collaborative decision-making (A-CDM) all contribute to optimized taxiing and airport efficiency.

Conclusion

Taxiing is a vital, regulated component of flight operations, ensuring the safe and efficient movement of aircraft between all ground-based facilities at an airport. It involves careful coordination between pilots, ATC, and ground staff, and adapts to a wide range of operational scenarios, environmental conditions, and aircraft types. Adhering to best practices and established procedures during taxiing helps prevent accidents, reduces delays, and supports the overall safety and effectiveness of modern aviation.

References

• Federal Aviation Administration (FAA) Pilot/Controller Glossary
• ICAO Annex 14 – Aerodromes
• Eurocontrol A-CDM Guidelines
• FAA Airplane Flying Handbook (Chapter on Ground Operations)
• FAA Ground Operations Guidance