Assessment of critical resource use in aircraft manufacturing [original]

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https://doi.org/10.1007/s43615-022-00157-x

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ORIGINAL PAPER

Assessment ofCritical Resource Use inAircraft

Manufacturing

IuliaDolganova1 · VanessaBach1 · AnneRödl2 · MartinKaltschmitt2 ·

MatthiasFinkbeiner1

Received: 8 September 2021 / Accepted: 13 January 2022 /

Abstract

The global aircraft fleet has been expanding worldwide, leading to a high demand for

primary resources. Simultaneously, recycling initiatives for decommissioned aircraft are

still incipient. Following circular economy principles, the aims of this paper are to iden-

tify potentially critical resources used and related environmental impacts, to derive recom-

mendations regarding recycling, and to analyze the influence of increasing utilization of

lightweight composite materials in aircraft manufacturing. It was identified that the engine

is the structure containing resources with the highest scarcity, with tantalum dominating

seven of the eleven analyzed impact categories. Aluminum, titanium, and nickel were

shown to lead to the highest environmental impacts. Hotspots in the criticality and envi-

ronmental assessment often occur due to alloying resources with a low mass share. It was

shown that aluminum and steel alloy recycling should be prioritized. A higher lightweight

composite material share in the aircraft increases impacts in the categories climate change

and fossil resource depletion by 12% and 20%, respectively, whereas the impact of the cate-

gory acidification, political stability, and demand growth decreases by 16%, 35%, and 60%,

respectively.

Keywords Aircraft· Resources· ESSENZ· Criticality· Life cycle assessment

Introduction

The relevance of the air transportation sector has been increasing in the last decade, mainly

driven by factors such as low air fares and better living standards [1]. According to the

most recent forecasts, between 2017 and 2036, the number of airline passengers worldwide

is expected to grow by an average of 4.7% yearly [2]. By 2037, the annual number of pas-

sengers is predicted to reach up to 8.2 billion [3]. To satisfy this increasing demand, the

aircraft fleet will almost double in the next 20 years [4, 5].

* Vanessa Bach

vanessa.bac[email protected]

1 Technische Universität Berlin, Strasse des 17. Juni 135, 10623Berlin, Germany

2 Technische Universität Hamburg, Eissendorfer Strasse 40, 21073Hamburg, Germany

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In the last 30 years, the primary resource demand rose worldwide by overall 50%

[6, 7] and is projected to more than double from 79 Gt/a in 2011 to 167 Gt in 2060,

whereas metals are expected to grow the fastest [8]. The global aerospace industry alone

consumes 770 kilo tons of resource per year [9]. Simultaneously, the topic of resources’

criticality has become more relevant in recent years due to limited availability of certain

resources. Criticality is defined as supply risk (probability of supply disruption) and the

vulnerability to this supply risk [10–12]. Several studies on country level (e.g., [13–16])

as well as product level (e.g., [12, 17–20]) including the mobility sector (e.g., [21–25])

have been carried out in recent years to assess resources’ criticality.

In this context, a circular economy approach is a precondition for achieving climate

neutral production processes. The concept of circular economy emerged in the last dec-

ade considering the scarcity of natural resources counterposed to the growing demand

for them due to, e.g., increasing population. While most of the studies apply this con-

cept for increasing the recycling or the reuse rate of products, a social dimension seems

to be missing [26]. The ESSENZ method, applied in this paper, addresses the criticality

of resources also incorporating societal aspects [27].

Usually, an aircraft is in operation for about 30 to 40 years. Considering the age of

the current aircraft fleet, about 18,000 passenger aircraft will be decommissioned in the

next 20 years [28]. Some aircrafts are used for spare parts, sold to developing countries

or eventually brought back to service in the case of an increased demand. Notably, the

most common practice for decommissioned aircraft is their disposal in deserts of former

airports—the so-called aircraft graveyards [29, 30], where they are simply parked for

an undefined time period. Even though some initiatives for aircraft recycling have been

already developed and partly implemented (e.g., PAMELA project) [31–33]), they are

still very incipient, also because there is no international regulation for the end-of-life

handling of aircraft.

As aircraft are composed of a number of different resources, including aluminum, tita-

nium, nickel, and steel alloys, which are easily recyclable [34], these aircraft graveyards

can be seen as a great source for secondary resources, especially considering that some

of these resources might become scarce in the next decades. Also, it was already dem-

onstrated that 80–85% of an aircraft’s weight could be recycled [32]. Thus, it should be

identified which resources to focus on for recycling to reduce overall criticality and envi-

ronmental impacts of the aircraft manufacturing.

As shown in Fig.1, a new trend in the aircraft industry is the increased utilization of

lightweight composite materials, such as carbon fiber reinforced plastic (CFRP) or glass

fiber reinforced plastic (GFRP) [35, 36]. It is reported that the fuel use of aircraft with a

higher proportion of composites materials is around 25% lower than a reference aircraft

based mainly on aluminum parts [37]. Thus, the integration of composites materials in the

aircraft manufacturing may significantly reduce emissions throughout the operation phase

[38–40].

However, the resource use of aircraft during the production and recycling phases is not

fully addressed in these publications. As carbon fibers are mainly produced from fossil fuels,

their dependency on these resources is high. Methods for CFRP recycling are still under

development [39, 42, 43]. Currently, lightweight composite resources are more likely to be

landfilled or burnt than properly recycled [44–46]. Thus, a comprehensive assessment of envi-

ronmental impacts and criticality of composite materials considering current and future use

is also included in this paper. Overall, the aims of this paper are (i) to identify the most criti-

cal resources used in aircraft manufacturing applying the ESSENZ method [47, 48] —further

explained in background "ESSENZ Method" section—(ii) to determine the environmental

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impacts of the manufacturing phase; (iii) to derive recommendations regarding recycling of

resources, and (iv) to analyze the influence of the increasing use of lightweight composite

materials and their impacts on resource criticality and the environment.

The Airbus A330-200 was selected as a reference aircraft, exemplary for the entire aircraft

which is a commercial passenger aircraft designed for medium to long-haul flights. Currently,

there are approximately 416 active A330-200 airplanes, and 199 are being stored [49]. The use

phase is not considered in this paper, although it has the largest environmental impact when

considering the entire life cycle of aircraft [44], and the use of fossil-based jet fuels is a hot-

spot in terms of resource use in general as well as critical resources. However, as the use phase

has these high impacts, the impacts of the manufacturing stage are comparably low. Thus, the

manufacturing phase is being disregarded by most of the authors. The focus of this paper is

deliberately on the manufacturing phase to identify hotspots only in this life cycle stage.

To achieve the aims of the paper, first the analyzed product system and the methodology

("Method") including the life cycle inventory are described. The results are presented for the

criticality assessment including long-term availability ("Criticality Assessment Including

Long-Term Availability"), environmental assessment ("Environmental Assessment"), recom-

mendations regarding recycling of resources ("Recommendations Regarding Recycling of

Resources"), and scenario analysis for increased use of lightweight composite information

("Scenario Analysis for Increased Use of Lightweight Composite Materials"). The underly-

ing assumptions of the case study are discussed ("Discussion"), and conclusions are drawn

("Conclusions").

Fig. 1 Material trends for Airbus and Boeing aircraft based on a comparison designed by Ilg (2015) [41],

showing the increasing share of composites materials in the most modern aircraft

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Environmental andSocial Impact Evaluation ofAircraft Production inExisting

Literature

There are only few publications depicting the LCA of an aircraft in detail. This is

mainly due to the lack of public available data from aircraft manufacturers. In fact, only

one peer-reviewed paper performing a complete LCA of an aircraft was found [44] and

one from an aircraft’s wing [50], while the remaining works originate from theses and

reports [40, 45, 51, 52]. There are also a few available publications focusing on the

comparison between metallic alloys and lightweight materials from an environmental

point of view [38, 39, 53]. The social dimension of aircraft manufacturing has not been

discussed so far, affirming the assumption of Nikolaou etal. (2021) [26] that most of

engineering works tend to disregard it even in a context of sustainability assessment.

Howe et al. (2013) [54] conducted an LCA of A320 applying the Eco-Indicator

method, where manufacturing phase was found to contribute with 0.089% to the life

cycle. The main impact occurred mainly due to use of CFRP (responsible for 45% of

the total manufacturing impact). While evaluating an Airbus A320-200 with ReCiPe

Endpoint method, Johanning etal. (2013) [51] concluded that material production and

other manufacturing-related processes bore less than 1% of the total aggregated impact.

Both authors assumed that the aircraft was solely composed by aluminum, steel, tita-

nium composites, and miscellaneous (without specification of what “miscellaneous”

could mean). Jordão (2013) [52] have estimated only the embodied CO2-eq emissions,

concluding that aircraft manufacturing was responsible for 0.05% of the total life cycle

impact of an Airbus A330-200.

Lopes (2010) [45] conducted a comprehensive life cycle assessment with detailed data

for the manufacturing, operation, and recycling of an A330-200. Three methods were

applied: ReCiPe Midpoint, Cumulative Energy Demand [55], and Ecological Footprint

[56]. Also here, the impact from manufacturing in most of the categories was very small

(ca. 1·10-6%). Nevertheless, manufacturing was assessed in detail with ReCiPe midpoint

method, concluding that the structure engine emerges as having the largest contribution in

most of the categories. Wojcieh (2015) [40] used data obtained by Lopes (2010) [45], and

by applying selected categories from ReCiPe Midpoint (climate change, terrestrial acidifi-

cation, photochemical oxidant formation, particular matter formation) also obtained mar-

ginal contribution of the manufacturing phase.

Asmatulu etal. (2013) [42] and Ribeiro and Gomes (2014) [29] raised concerns about

end-of-life and recycling of aircraft and made recommendations on recycling options.

While Asmatulu etal. (2013) [42] focused on estimating energy savings from the use of

recycled materials, Ribeiro and Gomes (2014) [29] developed a conceptual framework for

integrating end-of-life (EoL) already in the preliminary design of the aircraft. Energy and

cost savings were the most important aspects of the framework.

ESSENZ Method

The integrated method to assess resource efficiency (herein referred to as ESSENZ) [47,

48] allows for a comprehensive assessment of resources use by addressing environmen-

tal impacts, criticality, and long-term availability of resources as well as societal aspects

of resource utilization. Further details are presented in the Supplementary Information

– Sect.1.

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For measuring the long-term availability of resources, the abiotic depletion potential

(ADP) indicator based on ultimate reserves [57, 58] is applied. Criticality is assessed using

an approach developed for ESSENZ, which was identified as one of the best approaches to

address criticality aspects of products assessments [10, 59]. The following potential sup-

ply disruptions are considered in the method: concentration of production, reserves and

company concentration, feasibility of exploration projects, political stability, occurrence as

co-product, mining capacity, primary material use, demand growth, price fluctuations, and

trade barriers.

Societal impacts within the category societal acceptance are determined by two catego-

ries: compliance with social and environmental standards. As consumers and local commu-

nities become more interested in compliance with social and environmental standards, this

can become an additional constraint for companies when purchasing resources. For meas-

uring the category “Compliance with Social Standards”, child labor, high conflict zones,

and forced labor based on indicators of the Social Hotspot Database [60] are applied. The

indicator to measure the category “Compliance with Environmental Standards” is the

Environmental Performance Index (EPI) [61].

For the determination of environmental impacts, the life cycle impact assessment

method CML-IA [62] is applied for the impact categories acidification, eutrophication, cli-

mate change, and photochemical ozone creation.

Method

In the following, the product system, the corresponding system boundaries, and the

assumptions for the scenario with an increased share of lightweight composite materials

are presented.

The functional unit was defined as 1 (one) aircraft A330-200. The aircraft A330-200 has

been separated into six major structural components: wings, fuselage, vertical stabilizer,

horizontal stabilizer, landing gear, and engine. The aircraft A330-200 can operate with dif-

ferent engine types. As only data for the General Electric model CF6-80E1 are available

[45], this engine type is considered.

The weight of the aircraft is the manufacturer’s empty weight (MEW) as defined by

IVAO [63]. This includes the airframe structure and the engine, excluding the closed sys-

tem fluids as well as internal components of the aircraft such as textiles due do lacking

data. Electronic parts were examined only for the structure engine.

For determining the environmental impacts, the GaBi software with datasets of sphera

[64] and ecoinvent [65] was used. For the resource criticality assessment, only the bill of

materials (BoM) of which the aircraft is composed of has been taken into account.

The identification of the BoM of the product system is based on the work of Lopes [45],

as shown on Table1. As far as the authors are aware, no other data sources for aircraft are

available. However, to ensure that the applied data is adequate, the authors discussed the

BoM as well as some of the results with the major aircraft manufacturers that confirmed

that the overall data quality is fair to good. More information on the detailed alloys con-

sidered are presented in the Supplementary Information - Sect.2. Energy and water use for

the complete airplane production was retrieved from Spielmann etal. [66], where a similar

aircraft was analyzed.

As already shown in Fig.1, there is a trend to produce aircraft with an increasingly

higher share of composites. For the scenario presented in this paper, based on the example

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