Evaluating Flight Performance and Eye Movement Patterns Using Virtual Reality Flight Simulator

Summary

A new virtual reality flight simulator was built, which enables efficient and low-cost evaluation of flight performance and eye movement patterns. It also provides a high-potential research tool for ergonomics and other research.

Abstract

Efficient and economical performance evaluation of pilots has become critical to the aviation industry. With the development of virtual reality (VR) and the combination of eye-tracking technology, solutions to meet these needs are becoming a reality. Previous studies have explored VR-based flight simulators, focusing mainly on technology validation and flight training. The current study developed a new VR flight simulator to evaluate pilots' flight performance based on eye movement and flight indicators in a 3D immersive scene. During the experiment, 46 participants were recruited: 23 professional pilots and 23 college students without flight experience. The experiment results showed significant differences in flight performance between participants with and without flight experience, the former being higher than the latter. In contrast, those with flight experience showed more structured and efficient eye-movement patterns. These results of the differentiation of flight performance demonstrate the validity of the current VR flight simulator as a flight performance assessment method. The different eye-movement patterns with flight experience provide the basis for future flight selection. However, this VR-based flight simulator has shortcomings like motion feedback compared to traditional flight simulators. This flight simulator platform is highly flexible except for the apparent low cost. It can meet the diverse needs of researchers (e.g., measuring situation awareness, VR sickness, and workload by adding relevant scales).

Introduction

The European Aviation Safety Agency (2012) categorizes flight simulators as training facilities, flight and navigation program trainers, flight training equipment, and complete flight simulators¹. To date, a range of flight simulators is available for training, from low-level tabletop systems to highly complicated motion-based full flight simulators². The traditional simulator includes a flight dynamics model, a system simulation, a hardware cockpit, an external visualization, and an optional motion simulation³.

These traditional flight simulators have some advantages as effective flight training equipment. However, their cost is high and environmentally unfriendly, as the drive of each system requires substantial electrical energy, especially a full flight simulator, which requires high temperature and high-pressure fluid or air pressure, consumes much power and generates a lot of noise⁴.

However, a simple desktop simulator system is flexible and low-cost, with lower immersion and fewer interactions than a full flight simulator². Therefore, it is essential to develop new flight simulators that combine the advantages of desktop systems and full flight simulators (in other words, the flexibility of a tabletop simulation and the immersion and interaction level close to a full flight simulator).

With the development of computer technology, especially virtual reality (VR) technology, a new type of flight simulator based on emerging VR technology is becoming a reality. The VR-based flight simulator is flexible, portable, low-cost, and has fewer space requirements than conventional flight simulators⁵. Researchers have created flight simulators based on VR technology over the past 20 years^{6,7,8,9,10,11}; however, these VR flight simulators are mainly for flight training, and there are few for pilot selection. Still, with cost reduction and technology enhancement, VR-based simulators are changing and becoming feasible for personal selection. Some studies have used VR-based simulators for personal selection in different domains: Schijven et al.¹² selected surgical trainees using a virtual reality simulator. Huang et al.¹³ developed a psychology selection instrument based on virtual reality technology for air force pilot recruitment. Wojciechowski and Wojtowicz¹⁴ assessed a candidate's capabilities as an unmanned aerial vehicle (UAV) pilot based on VR technology. Given that pilot selection is critical for the aviation industry, it is pressing to develop a new VR-based flight simulator focusing on pilot selection, as large-scale pilot selection is susceptible to the cost of the simulator and demands in the portability simulator system.

Eye movements provide cues for a pilot's performance. Different studies have found that the eye-scanning mode distinguishes the performance between expert and novice pilots. By comparing the scanning pattern between experts and novices, experts' efficient and structural eye movement behavior and the inadequate scanning methods of beginners could be differentiated. Several aviation studies have found that pilots' eye-scanning strategy highly relates to the level of expertise^{15,16,17,18,19,20,21,22,23,24}. According to Bellenkes et al.²⁵, the duration of experts' fixations is shorter, and the frequency of their fixations on instruments is higher than that of novices. Almost the same conclusion was drawn by Kasarskis et al.²⁶, who discovered that expert pilots have more fixations combined with shorter durations than novices, suggested that expert pilots have a better visual mode than novices. In another study, Lorenz et al.²⁷ found that experts spend more time looking outside the cockpit than novices. These results have great practical value in the selection of newcomers.

Flight performance assessment is another critical factor for pilot selection. However, the following problems exist in pilot flight performance evaluation: conflicting expert opinions, more selection norms, and a unified selection theory. In the driving field, Horrey et al.²⁸ compared the absolute value of lane departure from the centerline for different experimental conditions to assess driving performance. Back to the aviation domain, the flight quick access recorder (QAR) records all sorts of pilot manipulation parameters, aircraft parameters, environments, and warning information during flight²⁹. More specifically, as the QAR indicators, the pitch angle is the rotation angle around the left and right axes of the aircraft³⁰, and the reference line (or the center reference line) is right in the middle of the red and green lines²⁸; these two flight parameters are used to evaluate the flight performance of participants with or without experience in the current study. These QAR data can be used to evaluate flight performance, yet to our best knowledge, they have seldom been used for personal training and selection in scientific research^31,32.

Measurements of eye movement patterns can be used to assess and predict flight performance and guide pilot training and selection. Gerathewohl³³ stated that the eye is the most important sensory organ of the pilot, processing 80% of the flight information. Pilots must acquire visual information from instruments in the cockpit and integrate it into a coherent image to manage the flight²². Further, optimal scanning behavior is essential to accomplish better flight performance¹⁵. However, no affordable flight simulator currently integrates an eye tracker to facilitate quantitative studies of the relationship between eye movements and flight performance.

The current study developed a new VR flight simulator to assess if participants with flight experience had better flight performance than those without flight experience. The VR flight simulator integrates eye tracking and a flight dynamics system allowing eye-movement pattern analysis and flight performance evaluation. In particular, it is worth mentioning that the VR flight simulator uses a VR eye tracker³⁴, not a glass-like or desktop eye tracker, to analyze the area of interest (AOI)-based eye movement without time-consuming frame counting.

Finally, the present work can lead to an omnibus measurement for pilot selection in the future, from eye scanning path to objective flying performance data. With the help of the virtual flight simulator, the cost of flight selection will be significantly reduced, and the norm of pilots can be formed based on extensive data gathering. The work fills a gap between conventional and desktop simulators for flight selection needs.

Protocol

All methods described here have been approved by the Institutional Review Board (IRB) of Tsinghua University, and informed consent was obtained from all participants. After completion, all participants were paid $12 (or a gift of equal value).

1. Participant selection

1. Recruit participants according to a prior study of power analysis using G*Power software³⁵ (see Table of Materials) to ensure the participant number meets the expected sample size given by G*Power, which equals 21.
   NOTE: The expected sample size given by G*Power refers to the estimated number of participants needed in a study to achieve a desired level of statistical power based on the specified effect size, significance level, and statistical test used. The expected sample size is an important consideration in research planning. It helps researchers determine the feasibility and cost-effectiveness of their study design and ensures that the study has sufficient statistical power to detect meaningful effects.
2. Ensure none participants have a history of epilepsy, heart or brain disease, recent endocrine or psychiatric medication, or severe skin allergies.
3. Use the Snellen eye chart (use the metric system 6/6)³⁶ to confirm that participants' vision is normal or corrected-to-normal and that they don't have any visual impairments like color blindness or color weakness.
4. Ensure that none of the participants have consumed alcohol or drugs within the previous 24 h that may affect their ability to fly.
5. Ensure the participants have had no less than 6 h of sleep and are in good mental condition before the experiment.

2. Flight simulator hardware

1. Check that all of the flight simulator's hardware is complete. According to its function, this hardware is organized into three modules (Table 1) (see Table of Materials).
   NOTE: Researchers need to touch a metal rod before touching the equipment to avoid the risk posed by electrostatic induction.
   1. Check the components of the VR, HMD (head-mounted display), and eye-tracking module with the help of Table 2.
   2. Ensure that all the flight simulator PC module components meet the following minimum requirements: 3.6G Hz processor, 4G internal memory, 64-bit operating system, and graphics card. The system will support all flight controllers.
   3. Check the components of the flight control module and ensure the device's parameter configuration is consistent with Table 3.
2. Install the hardware of the flight simulator according to the layout in Figure 1. Figure 2 shows how the hardware is connected.
   1. Join the throttle and control panel physically and treat them as a unit.
   2. Connect the throttle, joystick, and pedal to the flight simulator PC module via USB.
   3. Connect the HMD to the flight simulator PC module via the link box.
   4. Connect the base stations and VR controllers to the HMD via the VR software on the PC.

VR head-mounted display(HMD) and eye tracking module	1. Base Station
	2. VR HMD
Flight Simulator PC module	3. Flight Simulator PC
Flight control module	4. Flight Throttle
	5. Flight Joystick
	6. Flight Pedal

Table 1: Components of the three modules of flight simulator hardware.

Main component	Accessories
VR HMD	Headset cable (attached)
	Face cushion (attached)
	Cleaning cloth
	Earphone hole cap × 2
Link box	Power adapter
	DisplayPort cable
	USB 3.0 cable
	Mounting pad
Controllers (2018) × 2	Power adapters × 2
	Lanyards × 2
	Micro-USB cables × 2
Base Station 2.0 × 2	Power adapters × 2
	Mounting Kit (2 mounts, 4 screws, and 4 wall anchors)

Table 2: List of components of the VR HMD and eye-tracking module.

Device	Parameter configuration
Flight Joystick	Nineteen action buttons
	One 8-way "point of view" hat
	Several 3D magnetic sensors
	One 5-coil spring system
	One 16-bit resolution (65536 x 65536 values).
Flight Control Panel	Fifteen action buttons
	One TRIM wheel
	Five programmable LEDs
Flight Throttle	Seventeen action buttons
	One mouse hat with a push button
	One 8-way "point of view" hat
	Several 3D magnetic sensors
	Two 14-bit resolution
Flight Pedal	Tension between 2.5 kg and 5 kg
	Angle between 35° and 75°

Table 3: The parameter configuration of the devices of the flight control module.

Figure 1: The layout of the VR flight simulator hardware. Please click here to view a larger version of this figure.

Figure 2: The connection of flight simulator hardware. (A) Flight control module. The throttle and control panel are physically joined and treated as a unit. If the term "throttle" is used in this study, it refers to both the throttle and the control panel. (B) Flight simulator PC module. A computer that meets the requirements outlined in step 2.2. (C) HMD and eye-tracking module. The software development kits (SDKs) for eye tracking and the 3D engine are kept in sync when installed on the same computer. Therefore, the eye-tracking functions and the operating system interact and work together. Please click here to view a larger version of this figure.

3. Flight simulator software

1. Ensure all the software (see Table of Materials) has been installed before the experiment begins. Information about all software used in the experiment is shown in Table 4.

Name	Description
VR software	A widely used tool for experiencing VR content on the hardware.
VR app store	The app store for virtual reality where customers can explore, create, connect, and experience the content they love and need.
Eye-tracking software	Eye-tracking software developed by the research team via Eye-tracking and 3D engine SDKs.
FlySimulator	The main program of the flight simulator software, developed by the research team.
Screen recording software	A free and open source software for video recording and live streaming.

Table 4: Information about all software used in the experiment.

4. Preparation before launching the flight simulator

NOTE: If this is one's first time running the eye-tracking program, perform the additional steps according to Figure 3. The eye-tracking program will activate automatically after the initial run.

Figure 3: The additional steps when running the eye-tracking program for the first time. Please click here to view a larger version of this figure.

1. Ensure that the HMD is turned on and connected to the computer.
2. Place the base station diagonally to ensure the HMD can always be inside the base station's monitoring range. Keep the base station fixed to keep a stable VR environment.
3. Set up a standing-only play area according to the prompts given by the VR software on the computer.
   NOTE: The prompt allows a room-scale area or sets up a standing-only play area. Standing-only mode is generally used to experience VR scenes that do not require walking and can be selected when the user has limited space to move around. Therefore, in this experiment, set up a standing-only play area.
4. Set the eye-tracking calibration. The eye-tracking system must be recalibrated every time the participant is switched.
   1. Confirm that the participants are not using contact lenses, which causes eye tracking to malfunction.
   2. Open the eye-tracking calibration program using the VR controllers (see Table of Materials).
   3. Adjust the device height, interpupillary distance (IDP), and gaze point as the system directs.
   4. Get the participant's eyes to light up each spot for 2 s in a clockwise direction to verify the effectiveness of the eye-tracking calibration.
5. Connect the tuned flight control module and large screen display (i.e., at least a 27 inch monitor) to the same computer as the VR HMD. The screen allows the experimenter to view what is happening in the VR HMD simultaneously.

5. Experimental procedure

NOTE: The experiment is divided into four steps: "collect information," "introduce the task and operation," "practice before the experiment," and "conduct a formal experiment." The experimental process is summarized in Figure 4.

Figure 4: The flowchart of the experiment. Please click here to view a larger version of this figure.

1. Collect information from participants (15 min).
   1. Fill out the payment details form with the payment information of the participants.
   2. Inform the participants to read the informed consent document and sign it.
2. Introduce the task and simulator operation to the participants (5 min).
   1. Explain to the participants the traffic pattern and map (Figure 5).
   2. Instruct participants on how to use the VR flight simulator.
   3. Inform the participants that they can leave the experiment if they experience discomfort while simulating a flight.
3. Ask the participants to practice using the VR flight simulator (15 min).
   1. Fit the VR HMD to the participants and calibrate the eye movements. Adjust the device height, interpupillary distance (IDP), and gaze point as instructed by the system.
   2. Open the screen recording software.
   3. Launch the FlySimulator program to assist participants with flight training.
   4. Instruct the participants to use the flight pedal, joystick, and throttle in concert to steer the aircraft as closely as possible to the reference line of flight (Figure 5).
   5. Reset the flight throttle and engine switch buttons after exiting the FlySimulator program, and stop recording the screen after the subject has completed the practice.
4. Conduct formal flight experiments (20 min).
   1. Put on the VR HMD for the participants, and run OBS Studio to start recording the screen.
   2. Start the FlySimulator program, choose a fit perspective, start the engine, let go of the parking brake, and put the flight throttle to full.
   3. Exit the FlySimulator program, then reset the flight throttle and engine switch buttons. Stop recording the screen.

Figure 5: The traffic pattern for the VR flight simulator. The pitch angle is the rotation angle around the left and right axes of the aircraft, and the reference line (or the center reference line) is right in the middle of the red and green lines. Please click here to view a larger version of this figure.

6. Data analysis

1. Analyze eye movement data.
   1. Divide five area of interest (AOI) zones in this study; for more information about the calculation of AOIs, see Figure 6, based on the actual panel of the flight cockpit corresponding to the flight cockpit instrument (Figure 7).
   2. Calculate the AOI difference test using the percentage of dwell time in the AOI zone³⁷, given the equipment feature of the VR oculomotor used in this study.
      NOTE: The average percentage of dwell time is the cumulative percentage spent looking within an AOI divided by the total fixation time and averaged across participants.
2. Analyze flight performance data with custom-developed programming scripts using Python 3.10. The core algorithm for performance metrics was adapted from the QAR analysis method, inspired by the 35 BAE-146 aircraft QAR data provided by the National Aeronautics and Space Administration (NASA)³⁸.
   NOTE: Flight performance indicators for this study: the total flight time (the total length of time from takeoff to landing for each participant, in seconds), pitch angle 1 s before landing (pitch angle of the aircraft 1 s before landing, obtained from raw data, in degrees), mean distance to reference line (mean error of the spatial distance between the aircraft and the reference line during flight, in meters), and standard deviation of distance to reference line (standard deviation of the spatial distance between the plane and the reference line during flight, in meters).
3. Conduct the statistical analyses.
   1. Use the Shapiro-Wilk test³⁹ to confirm the data's normality.
   2. Use statistical software (see Table of Materials) for descriptive statistics, Mann-Whitney U test, and Student's t-test.
   3. Depict the violin plots to indicate better the shape of the data distribution⁴⁰.
      NOTE: The explanation for the effect size measured using Cohen's d is as follows: 0.1 is very small, 0.2 is small, 0.5 is medium, 0.8 is large, 1.2 is very large, and 2.0 is huge^41,42. The significance level was set at p < 0.05.

Figure 6: AOI preprocessing and calculating flow process. Sections 1 to 4 describe how the present study processed the pilots' eye movement data up to the independent-sample t-test. Please click here to view a larger version of this figure.

Figure 7: Schematic diagram of AOI division of flight instrument. The function of instruments: (A) The airspeed indicator indicates the aircraft's speed relative to the air. (B) The altitude indicator shows the aircraft's pitch and roll altitude. (C) The vertical speed indicator indicates the aircraft's ascent or descent speed. (D) The altitude indicator indicates the aircraft's barometric altitude. (E) The engine speed indicator indicates the speed of the aircraft engine. Please click here to view a larger version of this figure.

Results

For the current experiment, 23 experts with flight experience and 23 novices without flight experience were chosen. The participants were between 25 and 58 years of age (experts: M = 32.52 years, SD = 7.28 years; novices: M = 29.57 years, SD = 5.74 years). The gender of all participants was male. All the novices were recruited from Tsinghua University (students or faculty), and all the experts were from China Eastern Airlines.

Eye movement

Discussion

The current study assessed if participants with flight experience had better flight performance than those without flight experience in a VR-based flight simulator. More importantly, it evaluated whether a more optimized eye movement pattern could be found in these participants with better flight performance. The results have significant differences between participants with and without flight experience in three key flying QAR indicators: pitch angle 1 s before landing, the mean distance to the reference line, a...

Materials

Name	Company	Catalog Number	Comments
3D engine SDK	Epic Games	Unreal Engine 4 GameAnalytics Unreal SDK	This SDK is a powerful yet flexible free analytics tool designed for games.
CPU	Intel	IntelCore i9	One of the most powerful CPU on the mainstream market.
Eye tracking SDK	Tobii	Tobii XR SDK	This SDK provide device agnostic access to eye tracking data to allow development for headsets from many different hardware vendors and is not limited to devices using Tobii Eye Tracking hardware.
Eye tracking software	Developed by the research team		A program that tracks the movement of a person's eyes while they are using a virtual reality HMD.
FlySimulator program	Developed by the research team		A software that simulates flying experiences in a virtual environment, using VR HMD and hand-held controllers.
Graphics card	NVIDIA	GeForce RTX 3090 10496 NVIDIA CUDA Cores 1.70 GHz Boost Clock   24 GB Memory Size GDDR6X Memory Type	One of the most powerful graphics card on the mainstream market.
Operating system (OS)	Microsoft	Windows XP	An operating system (OS) developed and exclusively distributed by Microsoft Corporation
Replica control panel	THRUSTMASTER	2960720 2971004 2962072 2960748 2960769	U.S. Air Force A-10C attack aircraft HOTAS
Replica joystick	THRUSTMASTER	2960720	U.S. Air Force A-10C attack aircraft HOTAS
Replica pedal	THRUSTMASTER		TPR pendular rudder
Replica throttle	THRUSTMASTER		U.S. Air Force A-10C attack aircraft HOTAS
Screen connected to PC	Redmi	RMMNT27NF, 27-inch, 1920 X 1080 resolution ratio	Screen allows the experimenter to simultaneously view what is happening in the VR HMD
Screen recording software	OBS Project	OBS Studio Version 28.0	A free and open source software for video recording and live streaming
Statistical power analysis software	Open-Source	G*power Version 3.1.9.6	A free and user-friendly tool for estimating statistical power and sample size.
Statistical software	IBM	SPSS Version 24.0	A powerful statistical software platform
Versatile statistics tool	GraphPad Software	GraphPad Prism Version 9.4.0	A versatile statistics tool purpose-built for scientists-not statisticians
VR app store	HTC Corporation	VIVE Software 2.0.17.6 / 2.1.17.6	An app store for virtual reality where customers can explore, create, connect, and experience the content they love and need.
VR head-mounted display (HMD)	HTC Corporation	VIVE Pro Eye	A VR headset with precision eye tracking
VR software	Steam	Steam VR Version 1.23	A tool for experiencing VR content on the hardware