Extended reality (xR) flight simulators as an adjunct to traditional flight training methods: a scoping review

Over the next 20 years, it is predicted that an additional 760,000 new pilots will be needed to meet the growing demands of the global aviation industry. With current training capability, this may be difficult to achieve. A potential means of improving the efficiency and lowering the cost of flight training, which arguably may be prohibitively expensive to many potential trainee pilots, is to use extended reality simulation in place of traditional flight simulators and aircraft for at least some of the required training. To provide a better understanding of the possibilities in this regard, and where current research has advanced, a scoping review was undertaken. In total, 18 studies were identified as meeting the inclusion criteria. It was concluded that extended reality technology has the potential to be successfully employed in flight training—saving time and money, whilst also enabling increased training capability, although some potential limitations were identified. The interest in this technology, combined with evidence pointing to its potential usefulness in flight training, suggests that further examination in this area by academia and industry is warranted.


Introduction
Prior to the COVID-19 pandemic, the global aviation industry was experiencing sustained growth, whilst concurrently suffering from a significant shortage of qualified, experienced pilots [1].At least part of this shortfall is believed to be due to insufficient training capacity to meet demand, and the prohibitive costs of flight training [1].
Once the industry has recovered from the effects of COVID-19, it is predicted that an additional 260,000 to 350,000 additional pilots will be needed over the next decade [1,2].Based on a 20-year fleet forecast for commercial aircraft, aircraft utilisation, attrition rates, and regional crewing differences, this equates to a requirement of up to 763,000 new pilots by 2039 [3].
It takes approximately 24 months to train a multi-engine, instrument-rated commercial pilot [4].However, as many airlines now require pilots to have a university degree [5], in addition to their licences, ratings and hour requirements, it can now take up to 48 months before a newly qualified pilot graduates flight training.Even then, newly qualified pilots, who only have the minimum hours required to hold a licence, may find it difficult to gain employment without first gaining experience.
Pilots train in both real aircraft and using simulation.Traditional flight simulators are typically expensive (US$10K to US$10M) and require specialist simulator staff and flight instructors to assist in their operation [6,7].However, extended reality (xR) [including virtual reality (VR) and mixed reality (MR)] is increasingly of interest to the aviation industry for its potential in flight training [8].xR-based simulators generally do not require specialists to operate and offer student pilots the opportunity to complete at least part of their training in a self-paced, learner-centric, collaborative environment, where autonomy and individualised training are encouraged [9].
By implementing xR technology in the form of virtual reality flight simulators (VRFSs), time and cost reductions could be made by substituting actual aircraft flying hours with relatively affordable simulator training [10,11].VRFSs may also have the ability to reduce the scale of operations, specifically in areas such as airport and airways charges, maintenance provision and the quantity of fuel (and other carbon-based materials) consumed, thus simultaneously lowering the costs and the negative environmental impact of aviation training [11][12][13][14].These latter potential advantages would also bring operators in line with environmental initiatives such as ICAO's Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) [15].
Better use of training time allocations, fewer delays or cancellations due to weather, or unavailability of aircraft due to maintenance issues, results in less time required to train pilots.A reduction in airframe hours and fuel usage, less maintenance and a marked reduction in the associated ancillary logistic costs might also lead to additional financial savings.A recent cost-benefit analysis [11] found that the US Air Force (USAF) alone could make savings of tens of billions of US dollars to fixed and variable operating costs over the next decade by implementing xR flight training in the form of the Pilot Training Next (PTN) initiative.It is suggested then that in the civil sector, potential operational savings such as these could be passed on to the consumer in the form of reduced training fees.This in turn could increase the attractiveness of a career in aviation to a broader base of potential student pilots to whom at present the cost of flight training is prohibitively high [16,17].
In the current scoping review, we seek to systematically collate the current evidence on whether xR technology has the potential to be used as an adjunct to existing flight training methods already employed by civil FTOs worldwide.Our research question, therefore, is 'What is the nature of the evidence to support the use of extended reality (xR) flight simulators in traditional flight training methods?'The objectives of the current ScR were to: (1) identify all relevant literature to assist in answering the RQ, and (2) what currently is the body of research and what further research might be required.
This review may assist and guide researchers interested in the use of xR in aviation training to best decide the direction future research might proceed and what is the current state of evidence and the methods that have provided it so far.

Method
Systematic literature searches of the academic databases, Web of Science, Scopus and Google Scholar were performed via the bibliographic platform EndNote to identify journal articles, conference proceedings, reports and unpublished grey literature that were published in English only relating to the use of xR in aviation.The following Boolean search terms were used: (1) "flight sim*" AND "virtual reality" OR "mixed reality" OR "extended reality"; (2) "flight training" AND "virtual reality" OR "mixed reality" OR "extended reality"; (3) "pilot training" AND "virtual reality" OR "mixed reality" OR "extended reality" and (4) "aviation training" AND "virtual reality" OR "mixed reality" OR "extended reality." Applying the Joanna Briggs Institute concept of population, concept, context (PCC) protocol [18], inclusion criteria were that study populations should be pilots of an aircraft (qualified or training), aircraft type may be fixed-, rotarywing, or UAV, the study should employ xR (VR or MR) flight simulation technology and the research should relate to flight training.
Two preliminary screening steps were taken.For Google Scholar search returns only, due to the number of results envisaged to be returned, and as recommended in previous studies [19][20][21], only the first 150 results were considered for inclusion.Following this, a title-only screening was carried out on all results returned from all sources, to identify returns that were obviously not relevant.
One author (GR) completed the initial database searches, and both authors decided which of the initial search returns satisfied the inclusion/exclusion criteria.The initial review of all studies was undertaken first by GR and then by AG.Any disagreements were to be settled by discussion, or, where agreement could not be reached, a third party independent of the study was to be asked to arbitrate.
Following the full-text review, a data extraction table was populated according to suggestions made in the JBI Reviewer's Manual [18,22].This included data, relating to: author(s), year of publication, title, publication source, country of origin, aims/purpose, population, method, concept, conclusions and key findings (see Tables 1, 2).

Results
Initial searches returned a total of n = 871 potential studies of interest.After the removal of n = 104 duplicates, screening by title led to a further n = 584 studies being omitted as they were not relevant.The abstracts of the remaining n = 183 were screened, after which a further n = 121 studies were excluded as being not relevant, leaving n = 62 studies identified as of potential or probable interest.Following the full-text screening, a further n = 37 studies were discounted for reasons such as the study was not relevant, the full text was not accessible, or it was not available in the English language.At this point, two further studies were identified and added following a review of the references, meaning n = 27 studies were subjected to the final in-depth full-text screening.During this final stage, a further n = 9 studies were excluded because they were either not relevant, participant 'n' details were not specific, it was discovered they were duplicate studies published using a different title or were not empirical.The n = 18 remaining studies were selected for inclusion in the scoping review.No additional studies were acquired as a result of the personal or public requests made to authors, ResearchGate or LinkedIn.
Figure 1 illustrates the stages of the literature search and details the number of studies screened at each stage, including the number of those studies included/excluded
The majority of the included studies, n = 11 (61%), focussed on civilian flight training, with the remaining n = 7 (39%) focussing on military flight training, although interestingly, n = 1,099 (76%) participants were military and n = 339 (24%) were civilian.Of the n = 1,438 participants in the included studies, n = 205 (14%) were qualified pilots, who held a cross-section of licences from PPL to ATPL (or the military equivalent), n = 1048 (73%) were student pilots undergoing formal flight training and n = 185 (13%) were unqualified non-pilot participants under instruction.
A summary of the conclusions and key findings (see Table 1) of the included studies suggested that n = 2 studies (one descriptive, one observational) explicitly reported that xR could offer some degree of cost savings in pilot training and n = 4 (two observational and two descriptive) stated pilot training time could potentially be reduced.Thirteen studies (four quasi-experimental, three qualitative questionnaires, two observational, two descriptive, one correlational and one experimental) reported positive learning experiences, and n = 5 (two correlational, one observational, one quasi-experimental and one descriptive) stated that xR was potentially as good as legacy methods.Although xR could potentially reduce the actual number of flying hours required, it should be remembered that there will be a finite limit to this number as flying a real aircraft is, presently, still a regulatory requirement to gain a pilot licence.In the future, aviation  The team believes this student-driven approach will reveal learning patterns that can help inform track selection On average, PTN students completed their first successful solo flight on their 7th or 8th flight whilst traditional UPT students solo, on average, on their 13th or 14th flight Long term, PTN expects to use its data analysis to inform the development of cognitive models which will be used to predict the success of the trainees in their future training PTN can develop these competency models due to its focus on emerging technologies and data collection Xi, Z McGowin, G Fiore, S Newton, O Sukthankar, G Oden, K (USA) [30] Mixed methods Quantitative: correlational design Qualitative: questionnaire Training in five sections: aircraft model; aircraft controls; flight manoeuvres; flight instruments; simulator tasks Participants were tested on the concepts they learnt using a questionnaire consisting of ten recall questions, ten descriptive questions and ten conceptual questions The experiments show that it is feasible to accurately predict student failure on simple flight tasks from visual attention features gathered from the initial flight phase, combined with knowledge mastery features The results affirmatively answer all research questions The findings in this study provide important stepping stones towards the long-term vision of scalable, automated delivery of flight instruction using off the shelf virtual reality headsets  [32] Qualitative eight-question survey A sample training application was created in a VR environment to familiarise students with the essential elements of a Socata TB-9 "Tampico" aircraft cockpit The exercise was programmed as a fully immersive VR lesson that replicated the interior of the aircraft, based on photographs, to facilitate the learning of pre-start cockpit procedures The study draws no supported conclusions and fails to answer the RQ Whitson, R (USA) [33] Quantitative between subjects, quasi-experimental method During the pre-test, participants flew over an urban environment Under the 'simple' post-test landing condition, participants flew over large fields with scattered trees Results do not appear to support the idea that virtual reality is superior to training with a PC monitor.Once familiarised with the setup, however, there was some data to suggest that the VR group seems to perform better in the rich textures' environment Gustafsson, A (Sweden) [34] Qualitative questionnaires where the moderator first answered some factual questions connected to the participant's performance and then asked the participant to answer some questions connected to the usability attributes The focus of the thesis will be limited to  [36] Quantitative: repeated measures experiment The flight task starts with a short taxiing phase from the parking position, a take-off, and a left-hand traffic pattern at an altitude of 2,000 ft Most participants were able to safely and reliably complete the flight task after a short acclimatisation phase in the virtual environment The results show that the fidelity of the VRFS is significantly lower compared with the fidelity of a conventional flight simulator, and thus cannot substitute the latter, particularly if the pilot's behaviour and performance are to be as close to reality as possible governing authorities may amend this, and reduce the number of flight hours required.Some form of negative training experience (i.e.functionality issue, simulator sickness) was reported in n = 2 quasi-experimental studies, whilst n = 3 quasi-experimental studies did not support the idea that xR flight training was better than the alternative legacy option.Distraction, stress and high cognitive load whilst in xR were reported in n = 3 (two quasi-experimental and one qualitative questionnaire) studies-although this might not necessarily be considered a negative outcome, with distraction mitigation and desensitisation being options to counter this.

Discussion
The scoping review identified 18 studies of interest published between 2018 and 2021 that met all inclusion criteria.Of these, the majority had been presented at conferences and subsequently published as conference proceedings, rather than as journal articles.This may have been an artefact of the speed at which technology is advancing in this area (i.e.quickly rendering technology and study data obsolete), making the delays sometimes associated with publishing in academic journals seem less attractive [37,38].However, it might also be that some of the studies lacked academic rigour and may not stand up to the stringent peer-review process of high-level journal publication [37].Another alternative is that the author/s could be continuing their work, including the incorporation of conference feedback, in this area and have, or intend to, submit the finished study to an academic journal for publication in the future [39].Nevertheless, it is unlikely that these papers will have been subjected to the level of scrutiny normally associated with journal publication; for this reason, any findings should be treated with caution; that said, this is an important finding of the current scoping review.
Most of the included studies were conducted by researchers based in the United States, with 7 of the 18 studies, and most of the participants, originating from the US military.This implies that the US military is currently investing significant time and resources into researching the potential benefits of xR for pilot training and is also reporting optimistic findings through some of their initiatives (i.e.Pilot Training Next).A potential explanation for this is that few, if any, civilian aviation organisations (e.g.flight schools) have the resources and financial capability to match the US military; therefore, in contrast, existing research from these sources appears to be limited in scale and number.In addition, few studies from the civil sector were solely focussed specifically on flight training, instead seeming to concentrate on nuanced areas of training such as learning, human-machine interaction and other human factors.
The majority of both the quantitative and qualitative evidence included in this review supports the potential of xR to be used as an instructional aid in the training of pilots who are currently using traditional flight training methods.The studies suggest that participants who undergo xR flight training are at least as good as those trained using traditional means [11,24,25].There is also evidence to suggest that xR flight training, in concert with traditional flight training, could decrease training time [11,23,29,31], reduce costs [11,23] and lower the environmental impact of flight training overall [11,13].
Some studies noted that XR flight training has some noteworthy limitations.VR, in particular, can result in breaks in presence 1,2 (BIP) [40,41] (i.e.feeling disconnected) between the participant and the physical world they occupy (e.g. a VR flight simulator with physical cockpit controls).This BIP can result in restrictions in operation, particularly when the pilot is required to engage with particular aspects of the physical cockpit environment/equipment (e.g., buttons, dials and switches) [12,36,41].MR, which combines images of the physical environment and VE, has the potential to overcome this limitation as it develops [25,42].It is also reasonably common to feel the effects of simulator or cybersickness (e.g.cybersickness symptoms include nausea, dizziness, disorientation and headaches and are related to classical motion sickness) [43] during xR exposure, particularly if a participant is susceptible to motion sickness, or new to xR [12,36], but not always, be overcome with continued exposure over time that may lead to the participant becoming desensitised [43].It is worth mentioning that conventional simulators as well as real aircraft are also known to cause motion sickness [10].

Limitations
There were at least three potential limitations identified during this Scoping Review.First, during the search and study identification phase, it is possible that not all of the studies relevant to answering the research question were successfully identified.Second, it is also possible that studies exist that have not, for various reasons (e.g.publication bias), been made publicly available.Third, due to financial constraints, only studies published in English were considered, 1 Presence (or telepresence as it otherwise known) is an inside-out view of the world where the participant sees and interacts with the VE (e.g. an aircraft cockpit) just as they might if they were physically present.It is the sense one gets of being in the virtual environment (VE). 2 Breaks in presence (BIP) are moments whilst exposed to a VE that a participant become aware of their real world setting and their sense of presence in the VE becomes disrupted.Extended reality (xR) flight simulators as an adjunct to traditional flight training methods:… 1 3 which prevented the potential inclusion of six of the identified studies.

Suggestions for future research
As is evident from the paucity of eligible studies focussing on the use of xR technology and/or VRFS use in flight training (particularly in the civil sector) that there is scope for more research to be undertaken.The greater the amount of data and level of understanding on a topic area such as this will enable those responsible for deciding what future iterations of flight training will entail.Specifically, to assist in achieving this goal, it is suggested that more research should be undertaken in areas such as BIP/disconnect-here the potential benefits of MR's perceived ability to reduce these effects could be further investigated.A comparative study involving civil FTOs could be conducted to assess differences between student pilot groups-some of whom used VRFSs in their training.In concert with a comparative study, a cost-benefit analysis could also be undertaken to compare the costs of differing flight training approaches (i.e.traditional versus VRFS) to gather data that might support the suggestions of cost-saving made in other studies.

Conclusion of scoping review
The purpose of this scoping review was to (1) answer the research question, (2) provide an overview of the topic and (3) determine the value of conducting a full systematic review.
Despite the aviation industry's proclamations to limit its environmental impact with initiatives such as CORSIA, as well as reducing training time and cost, whilst also increasing pilot throughput, only 18 studies that satisfied the inclusion criteria were identified.This number is low when considering the technological potential, level of innovation and the investment currently being seen in xR technology.From the limited number of studies available, however, there was some evidence to suggest that xR flight simulators could successfully be used in support of traditional flight training.
Overall, this scoping review determined that there is a lack of empirical, peer-reviewed studies in the area of xR flight training.Considering this finding, further investigations into whether xR can satisfactorily deliver an enhancement to traditional flight training methods are required.This is something that could be addressed by academic institutes, particularly those with close ties to commercial aviation.To redress the imbalance that currently exists with military studies, research of an empirical nature involving civil FTOs should be undertaken as a priority, so the results can be better applied to airline and civil aviation.It is suggested that a longitudinal study involving both instructors and students at a large FTO would in part fulfil this requirement and potentially provide data that could also apply to other commercial FTOs.
It is concluded that, at this moment, not enough highquality empirical evidence exists to warrant the conducting of a full systematic review.
Funding Open Access funding enabled and organized by CAUL and its Member Institutions.The authors did not receive support from any organisation for the submitted work.

Declarations
Conflict of interest All authors certify that they have no affiliations with or involvement in any organisation or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.The current review was work undertaken for the degree of Masters of Aviation by the first author (GR) [44].The second author (AG) was the thesis supervisor.
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Table 1
Data extraction table-publication details , a flight simulator based on immersive VR technology is presented: The virtual reality flight simulator (VRFS), which was developed by and is used at Airbus Group Innovations.To assess the fidelity of the system and the bias that is introduced by the virtual environment, the system is compared with a conventional hardware flight simulator

Table 2
Data extraction table-process and findings