What you need to know about Engine-Out Taxi-In

Pilots are the main actors to improve fuel efficiency since a lot of initiative to save fuel must be applied during flights.

That’s why this new series of articles will focus on giving you tips and tricks for many industry best practices for fuel efficiency.

After Continuous Descent Approach (CDA), let's focus on optimizing your ground operations.

There is one best practice which is quite simple to implement and that can yield significant savings if applied regularly: Engine-Out Taxi-In or Single-Engine Taxi-In (Engine-Out Taxi is a more general term that also applies to aircraft that have more than 2 engines).

What is Engine-Out Taxi-In?

Engine-Out Taxi-In (EOTI) is a fuel efficiency best practice that can be applied during the taxi-in phase, i.e. the taxi from the landing runway to the block (another best practice called Engine-Out Taxi-Out deals with the taxi from the block to the takeoff runway; it will be described in a future blog article).

Its principle is to perform this taxi with one or several engines (in the case of four engine airplanes) shut down to save fuel.

But, to preserve engine life, it is very important to respect the engine cool-down time prescribed by the manufacturer before shutting down an engine. As a consequence, Engine-Out Taxi-In is only applicable when taxi-in duration is longer than engine cool-down time.

Figure 1: Engine-Out Taxi-In Best Practice

Is Engine-Out Taxi-In efficient? What are the benefits?

Wondering what are the typical fuel savings for shutting down one engine?

The chart below shows what are the typical fuel saved and the typical cooldown time, depending on the aircraft type:

Figure 2: Typical fuel saved and cooldown time, depending on the aircraft type

But remember the math of airlines fuel efficiency: it consists in multiplying small quantities by big numbers.

This means that even the last seconds count. Let’s take the example of a very short taxi of 3 minutes and 45 seconds on an A320 or a B737 that have an engine cooldown time of 3 minutes. You might consider that these 45 seconds don’t make such a difference.

Yet these 45 seconds of single engine taxi represent 45 s x 4kg / min = 3kg on each flight. Now imagine you operate a mere 30,000 flights per year, the total saving would be 3 kg x 30,000 flights = 100,000 kg.

Can pilots really make a difference?

Many pilots are reluctant to apply Engine-Out Taxi In, mostly for the following reasons:

• An uphill taxiway (for example in Amsterdam-Schiphol airport)
• During the final turn, the fear of not being in the right way
• Overconsumption at the stops & go
• Runway crossings (engine should be shut down after having crossed the runaways)

If you want to increase Engine-Out Taxi-In application rate without compromising safety, here are some tips:

• First, provide guidance on how to perform Engine-Out Taxi-In and clear procedures that explain when to apply it or not
• Bring tangible facts about the feasibility conditions of Engine-Out Taxi-In best practice at the different airports of your network. This aims to to facilitate change management within the pilots.
• Communicate regularly with pilots to engage them and remind the procedure and its safety considerations.
• And finally, in our opinion, the most efficient way to increase Engine-Out Taxi-In application is to empower pilots with a tool (such as a mobile app) which enables them to have a personal and confidential feedback on each of their flights and best practices, including 3D visualization.

If we take the example of Ukraine International Airlines: before using SkyBreathe® MyFuelCoach™, as can be seen in February 2017, less than 20% of Ukraine International Airlines’ pilots were using Engine-Out Taxi-In.

Using the mobile app, by October 2017, that had risen to nearly 80%:

Figure 3: Engine-out taxi in application from beginning of application
of SkyBreathe® MyFuelCoach™  application for pilots

[Case study] Fuel management at Ukraine International Airlines

You want to keep a data sheet about Engine-Out Taxi-In?

Download the extended version of this article: