The carbon footprint of air travelers starts before aircraft takes off. Let’s review which are the carbon emissions on ground and what can be done to reduce them.
Carbon counter ticks well before boarding
The two main Paris airports -CDG & ORY- calculated their respective carbon footprint (note 1). We will be excluding the aircraft taxi phases which will be treated separately. The overall impact per passenger (pax) on ground is evaluated to be 7,75 kg CO2e per departure. The break down can be summarized as shown below.
Assuming similar estimate at arrival, the balance sheet accounts for 15,5 kg CO2e per passenger for a full trip, 73% being under the Airport scope and the remaining portion is coming from the static aircraft operation on ground (APU & Ground Support Equipments -GSE-)
Looking at this from a global flight impact perspective, the ground operation can represent up to 14% for a short haul flight (see note 2). This is not negligible.
A growing number of worldwide airports has decided to reduce their carbon emissions, joining the ACA program (Airport Carbon Accreditation). Six different levels going from carbon foot print assessment to offset of residual emissions are gradually attributed depending on achievements. The efforts are spread among the airport facility management, the surrounding transportation infrastructure (pax & employee commute impacts being predominant) and airlines operations on ground. On that aspect, more and more airports are enforcing gradual limitations on APU run durations to reduce carbon emissions (scope 3), air particles & noise pollution. It becomes not unusual to see APU usage being restricted to 10 min before departure & 5 min after arrival (CDG, ORY & TLS practices).
Mobile Air Conditioning & Ground Power Units can substitute the APU by providing cooled air and 115 V AC/ 400 Hz power to the aircraft. Powered by diesel engines, the overall carbon emission of such devices is cut by a factor 9 compared to the APU at similar load factor (note 3)
Connecting the Aircraft to Fixed Electrical Ground Power and pre-conditioned air at the gate (FEGP) provides even more gains depending on the domestic electrical mix. In France (average of 60 g of CO2 per kWh), replacing the APU by FEGP cuts carbon emission by a factor 1000 on a single aisle aircraft (note 4). Benefits go beyond carbon emission reduction as such application improves air quality by getting rid of NOx and particles present in engine exhaust gases.
While equipping airports with FEGP requires massive & long term investments (whose only biggest airports would be able to bear), the research of optimum energy use on ground provides immediate gains. With that regard, digital solutions constitute an efficient lever to quickly optimize APU & ground power usage based on cabin cooling needs as a function of departure time, availability/ location of ACU, etc. Savings are immediate and investments kept minimal.
Real time connectivity to the A/C is the back bone of such a digital approach where datas are treated real time and aircraft operations adjusted live. FlightWatching has developed such algorithms with materialized significant savings on fuel and carbon emissions.
Aircraft movement on Ground.
Aircraft movements in the CDG & ORY airports were also analyzed from carbon emissions perspectives. In 2018, the taxi, take off, climb and approach phases released a total of 1,2 Mtons of CO2e on those two airports. This represents 11,5 kg of CO2e per passenger with below break down.
Focussing on the movements occurring on Ground, the taxi phases (in and out) are accounting for 3,75 Kg of CO2e per passenger.
There are technical solutions to minimize carbon emissions of the Aircraft movement on ground thru the use of single engine ortaxi bots during Taxi In and Out runs.
While Single Engine in Taxi In (SETI) is already practiced by a non negligible portion of airlines (about 50% according to experts), Single Engine in Taxi Out (SETO) is more confidential because of runway clearance security requirements. SETO is most of times performed with the support of Air Traffic Control to ensure smooth aircrafts movements and adhoc routing in case return to gate is necessary (in case side engine(s) do not light)
Towing the aircraft up to departure stand using Taxi bots constitue one another option to limit carbon emissions associated to aircraft movements on Ground. While those devices are powered by diesel engines nowadays, their fuel consumption is significantly lower than jet engines (-75%). Electrical versions which are being developed will offer a bigger decarbonation potential.
When it comes to limit the use of APU or main engines on ground, the savings for the airlines go beyond fuel burn but also materialize thru maintenance cost reduction. This constitutes a true incentive for adoption.
How much Carbon emissions saving expected?
The Shift Project has evaluated the carbon emissions savings onFrance Domestic air traffic associated to the deployment of both FEGP and Electrical Taxi bots. As a background information, the below charts provide estimates of the annual Carbon budget devoted to Commercial Flights in France aligning with +2°C in 2100 with 66% success rate (Note 5).
The global carbon emission savings achieved by fully substituting the APU at the gate by electrical FEGP has been evaluated by. the Shift Project to be equal to 300 ktons of CO2e in France. This represents 4,5% of the global required efforts (6,65 Mt CO2 per year).
The carbon emissions savings associated to the generalization of electrical powered taxi bots on 90% of the SETI and SETO were evaluated by the Shift Project to be equal to 240 ktons of CO2e in France. This accounts for 3,6% of the annual carbon reduction objective (6,65 Mt CO2e)
While the full deployment of those technical solutions are a challenge which would probably take one decade as a minimum, the gains in carbon emissions savings can be considered modest (8,1%) with regards to the overall objectives. This being said, any percentage counts and any positive contribution can’t be discarded.
Whereas those results can’t be directly scaled at World Wide levels, (content of carbon within electrical mix being the primary reason), they give an order of magnitude of the savings which can be achieved if Aircraft ground power and movements get fully decarbonized.
We’ll explore the options to tackle the remaining (& biggest) chunk of required carbon emissions savings in further posts. Let’s stay tuned…
Note 1: ADP Carbon Assessment report dated 2018
Note 2: Assuming 110 g of CO2e per pax & per km. This is considering an average fuel consumption of 3,5 liter Jet A / pax per hour and a 80% load factor.
Note 3: Assuming a 15 liters / hour Diesel consumption for an ACU/GPU combo & 160 liters / hour Jet A consumption for a single Aisle APU.
Note 4: Assuming a 20 kW industrial electrical cooling unit used for a Single Aisle Aircraft.
Note 5: Including the carbon emission of 50% incoming international flights.