Why Airbus A320 pilots often taxi with just one engine

Passengers looking out of an Airbus A320 window before departure or after landing may notice an unusual sight. One engine is running while the other appears completely still.

Far from indicating a technical problem, the stationary engine is often part of a carefully planned operating procedure known as single-engine taxiing. Once considered an optional fuel-saving measure, it has become standard practice for many airlines as fuel costs, sustainability targets and operational efficiency have become increasingly important.

According to reporting by Simple Flying, Airbus has incorporated single-engine taxi-in procedures into its standard operating philosophy after operational data demonstrated the safety and effectiveness of the practice.

A procedure that has become mainstream

Single-engine taxiing was once primarily associated with low-cost carriers seeking to reduce operating expenses.

Over time, however, airlines across the industry adopted the practice as fuel prices rose and environmental concerns became more prominent.

According to Simple Flying, Airbus strengthened the practice by moving the single-engine taxi-in procedure from the Supplementary Procedures section of the Flight Crew Operating Manual (FCOM) into the Standard Operating Procedures chapter.

The change effectively made one-engine taxiing the manufacturer's recommended operating philosophy whenever operational conditions permit.

Airlines subsequently incorporated the updated guidance into their own operating manuals, making engine shutdown during taxi-in a routine part of post-landing procedures on many A320 flights.

Fuel savings drive the decision

The biggest advantage of taxiing on one engine is lower fuel consumption.

Jet engines are designed to operate most efficiently during cruise rather than while idling on the ground. Running both engines during long taxi periods consumes fuel without contributing to flight performance.

According to Simple Flying, shutting down one engine allows an Airbus A320 to save approximately:

• Around 4 kilograms (8.8 pounds) of jet fuel per minute compared with operating both engines at idle.
• Lower fuel costs during airport congestion.
• Reduced airport-level carbon emissions.

While the saving appears modest on a single flight, airlines operating hundreds of aircraft can achieve significant reductions over thousands of daily movements.

The operational benefit also supports broader industry efforts to reduce unnecessary fuel burn while aircraft remain on the ground.

One engine provides sufficient power

Many passengers assume both engines are required to move a commercial aircraft weighing tens of tonnes.

Modern turbofan engines produce far more thrust than is required for taxi operations.

According to Simple Flying, the CFM56-5B engines commonly fitted to the A320 family produce approximately 27,000 pounds (120 kilonewtons) of thrust each.

Once the aircraft begins moving, a single engine operating at idle generates enough power to maintain normal taxi speeds of approximately 15 to 20 knots.

Pilots may even need to apply brakes periodically because the idle thrust from one engine alone can continue accelerating the aircraft on level taxiways.

System upgrades have improved efficiency

Running one engine introduces additional technical considerations.

Aircraft electrical systems, hydraulics and cabin services normally rely on power supplied by both engines or the Auxiliary Power Unit (APU).

The APU itself is a small gas turbine engine positioned in the aircraft's tail. Although much smaller than the main engines, it also consumes fuel.

According to Simple Flying, the APU burns approximately 126 kilograms (277.8 pounds) of fuel per hour.

To maximise fuel savings, Airbus developed the Single Engine Taxi Without APU (SETWA) upgrade.

The modification allows aircraft to taxi safely using a single engine without relying continuously on the APU while maintaining fire protection systems and essential aircraft services.

The result is greater fuel efficiency and lower carbon dioxide emissions during ground operations.

Thermal management remains essential

Pilots cannot simply shut down an engine immediately after leaving the runway.

According to Simple Flying, aircraft engines operate at extremely high temperatures during flight and require a cooling period before shutdown.

The principal concern is a condition known as rotor bow.

If an engine is stopped while internal temperatures remain excessively high, uneven cooling may cause slight distortion of the engine's central shaft. Restarting the engine before temperatures stabilise could result in compressor blades contacting the engine casing, creating serious internal damage.

To prevent this, CFM56 engines require approximately three minutes of thermal stabilisation at idle power before shutdown.

Pilots carefully monitor this timing as part of normal post-landing procedures.

Safety remains the overriding priority

Although single-engine taxiing has become increasingly common, it is never mandatory.

According to Simple Flying, flight crews continuously assess operational conditions before deciding whether the procedure is appropriate.

Pilots may choose to operate both engines if factors such as:

• Wet or contaminated taxiways.
• Complex airport layouts.
• Heavy traffic.
• Tight gate manoeuvring.
• Aircraft technical considerations.

reduce the safety margin.

The captain retains final authority over whether single-engine taxiing should be used for any particular flight.

Future technologies may change ground operations

Aircraft manufacturers continue exploring alternative methods of reducing airport emissions.

According to Simple Flying, engineers are developing electric taxi systems that use electric motors integrated into landing gear wheels to move aircraft around airports without operating the main engines.

Although these technologies remain under development and have not yet entered widespread airline service, they could eventually reduce fuel consumption further during ground movements.

Until then, single-engine taxiing remains one of the aviation industry's simplest and most effective operational measures for improving efficiency. What passengers may see as one silent engine is, in reality, the result of carefully engineered procedures designed to reduce fuel burn, lower emissions and manage airline operating costs while maintaining the safety standards that underpin every commercial flight.