Single-Engine Taxi

Single-engine taxi is an operational procedure in which a multi-engine aircraft taxis to or from the runway with one or more engines shut down, using the thrust of the remaining running engines to move the aircraft on the ground. Widely adopted by twin-engine narrow-body and wide-body operators, single-engine taxi eliminates the fuel burn of non-contributing engines during what can be one of the longest non-flight phases of an aircraft's operating cycle — particularly at congested hub airports where taxi times can exceed 30 to 45 minutes — and delivers meaningful fuel savings and emissions reductions with zero capital expenditure and no modification to the aircraft.

What Is Single-Engine Taxi?

The procedure is typically applied during taxi-out at departure, where the second engine is not started until the aircraft is near the runway holding point, and during taxi-in after landing, where one engine is shut down immediately after clearing the runway and before the aircraft begins its taxi to the gate. For twin-engine narrow-body aircraft such as the Airbus A320 or Boeing 737, single-engine taxi-out typically shuts down one engine during pushback and the initial taxi phase. For quad-engine widebodies like the Boeing 747 or Airbus A380 — which are increasingly rare in modern fleets — two engines can be shut down during taxi, proportionally amplifying the savings. The technique requires no modification to standard airline operating procedures and is approved in aircraft flight manuals for all major commercial types.

How It Works in Practice

A typical twin-engine aircraft burns approximately 600 to 800 kilograms of fuel per engine per hour during ground operations, depending on thrust setting and auxiliary power unit usage. A 20-minute taxi-out with one engine shut down saves approximately 100 to 150 kg of fuel per departure. Multiplied across thousands of daily departures, these savings accumulate rapidly: Ryanair, which operates approximately 1,800 flights per day, reported fuel savings of approximately 15,000 tonnes per year from single-engine taxi operations. The procedure also reduces engine wear and maintenance costs, as turbine hot-section components experience thermal cycling every time an engine is started, and reducing the number of cycles per flight extends time on wing between maintenance visits.

Why It Matters

Single-engine taxi is among the most cost-effective operational efficiency measures available to airlines because its implementation requires only crew training and procedure update rather than capital investment. Airlines implementing the procedure typically see payback periods measured in days, not years. The technique also reduces airport air quality impacts: jet engine exhaust at ground level contributes to local NOx and particulate matter concentrations, and airports near residential areas face increasing regulatory scrutiny over ground-level air quality. Some airports in Europe and the United States now explicitly encourage or mandate single-engine taxi or offer priority gate assignment and reduced gate fees as incentives. The main operational constraints are safety considerations at airports with complex taxi routing requiring rapid thrust response, and noise considerations where engine start near noise-sensitive areas may require both engines running.

Key Facts and Figures

• Fuel saving per departure: approximately 100 to 150 kg for a twin-engine narrowbody on a 20-minute taxi.
• Ryanair reported approximately 15,000 tonnes of annual fuel savings from single-engine taxi procedures.
• Engine thermal cycles are reduced by approximately 0.5 to 1.0 cycles per flight for one-engine taxi-in and taxi-out.
• Reduction in NOx emissions from single-engine taxi on a typical 20-minute taxi: approximately 30 to 50 percent.
• CO2 reduction per departure: approximately 315 to 475 kg (burning 100 to 150 kg less fuel at 3.15 kg CO2 per kg Jet-A).
• The technique is standard operating procedure at most major European and North American carriers.

Related Concepts

Winglet Fuel Savings, Flight Path Optimization, Carbon Intensity, Contrail Management, Green Airport