1. Introduction
With the rapid advancement of the civil aviation industry, there is a growing demand for expert pilots who bear significant responsibility for ensuring safety [
1,
2]. Flight trainees, in their early stage of learning to fly, require training to develop their flying skills. The conventional approach to flight training involves utilizing flight simulators for simulation training. Therefore, accurate and efficient evaluation of flight trainees during flight simulation is of significant importance.
Reviewing the literature indicates that numerous investigations have been conducted in the field of flight training using flight data [
3,
4]. For instance, Kim et al. [
5] proposed an improved algorithm for quick access recorder (QAR) data recording and decoding, covering the entire process of conversion, design, development, and validation of data. Cohen et al. [
6] proposed a risk evaluation model for aircraft performance that integrates exceedance information, environmental information, and expert experience to assess daily flight performance. Moreover, Wang et al. [
7] utilized QAR data and the Analytic Hierarchy Process TOPSIS (AHP-TOPSIS) method to calculate subjective and objective weights to effectively overcome the challenges of incorporating expert knowledge and experience in flight quality evaluation. Gorinevsky et al. [
8] applied data mining techniques to distributed fleet monitoring (DFM) and Flight Operations Quality Assurance (FOQA) data collected from a commercial fleet to detect anomalies in aircraft data such as weight and angle of attack, as well as faults and deviations. Gómez et al. [
9] introduced an integrated flight data recorder analysis tool, FRiiDA, for military transport aircraft. This tool provides an integrated flight data recorder enabling preventive measures to ensure the quality and safety of aircraft. Yao [
10] designed an assessment index system using pilot physiological signals and flight operation parameters. In this regard, a pilot flight training quality assessment model was developed based on the backpropagation (BP) neural network, and the influence of each index on the assessment score was analyzed through the weight distribution of the trained network. The reliability of the model was verified through mathematical analysis. Zhang [
11] proposed a BP neural network assessment method for objectively evaluating test pilot piloting skills. The results demonstrated that the BP neural network method improves assessment accuracy and resolves the subjectivity issues of conventional assessment models. Yang [
12] established a pilot safety performance indicator preference model for flight school pilots based on grey entropy correlation analysis. The model was applied to analyze the impact of overrun events on safety performance and identify the main factors affecting pilot safety performance indicators.
In terms of flight safety evaluation based on data, numerous studies have been conducted worldwide. For instance, the U.S. Department of Defense [
13] established a system for assessing the operational quality of military pilots, based on established rules and standards. Furthermore, Malhotra [
14] presented the concept of clearing the Control Laws (CLAW) by Handling Qualities (HQ) assessment using a simulator, discussing challenges and the outcome based on flight test results of the actual air-to-air refueling (AAR) task. Sun [
15] demonstrated that the evaluation of flight maneuvering quality level is a crucial metric for the development of civil aircraft flight control systems. Cooper and Harper [
16] introduced the Cooper–Harper aircraft handling qualities scale, which rates the operational skills of pilots based on the mastery of operational control and stability. Among various indicators for assessing the handling skills of pilots, this scale focuses on the optimal choices chosen by pilots. Payne and Harris [
17] selected 12 key technical indicators and developed a pilot operational skill evaluation system to evaluate pilot operational skills in five aspects, including lift control, tilt control, balance ability, yaw control, and speed control. Finally, the system generates a 10-level skill rating for evaluating behavioral parameters at the operational level. You Xuqun et al. [
18] analyzed the requirements for pilot work, proposed a hypothetical model for evaluating the technical skills of pilots, validated the proposed model, and finally derived a four-dimensional evaluation model for airline flight skills to comprehensively evaluate the operational skills of pilots. Liu Zhongqi [
19] utilized pilot eye movement data to develop a BP neural network model for predicting and evaluating the flight performance of pilots with different skill levels during training and simulation. Mickael Rey et al. [
20] proposed a data-driven approach for classifying the safety or risk of civil aviation flights using data analysis methods and machine learning tools.
The performed literature survey indicates that most investigations in this field have focused on flight data, pilot physiological [
21,
22] and subjective data, and objective scales to assess the flight quality of civil aviation pilots. However, there is no comprehensive understanding of the flight quality of civil aviation pilots during the initial stages of flight training. This issue is particularly more pronounced during flight simulation. The present study introduces a novel approach to evaluating flight performance utilizing GBDT-PSO-CNN. The assessment is based on scoring data from simulated flights, integrated with real-time flight data. This combined approach ensures a precise evaluation of the pilot’s maneuvering performance, contributing to the enhancement of flight skill levels among trainees.
The terminology used in the literature in the introduction section is shown in the
Table 1 below:
2. Methods and Materials
The experimental process involves the utilization of a flight simulation trainer to provide a training experience for flight trainees. Data collected from the flight simulation trainer was utilized to organize the National Collegiate Flight Simulation Championship, encompassing a wide range of challenging scenarios. This championship provides a platform for students specializing in flight techniques to enhance their technical proficiency and gain practical experience in performing complex flight operations. Moreover, it offers participants a valuable opportunity to develop essential practical skills that are crucial to their future careers in aviation.
2.1. Participants
In this research, a total of forty male students who are pursuing a degree in flight technology from the College of General Aviation and Flight at Nanjing University of Aeronautics and Astronautics (NUAA) participated in the tests. Participants were aged from 20 to 22 years, with a mean of 21.2 years (SD = 0.68). The flight trainees participating in the experiment were members of the school’s flight simulation team, each with prior experience of over 40 h in flight simulation training. Additionally, these trainees were familiar with simulation software such as P3D and Xplane. All participants received training before the flight simulation.
The flight trainees admitted to the Flight Technology Program at NUAA undergo a rigorous selection process. They are admitted based on a physical examination conducted by the Civil Aviation Administration of China (CAAC) and the examination of higher education institutions. Upon admission, a flight trainee must progress through three key stages to become a civilian pilot as follows:
(1) Theoretical study phase at Nanjing University of Aeronautics and Astronautics;
(2) Sending pilot trainees to CCAR-141 flight schools approved or recognized by the Civil Aviation Administration of China for flight license training;
(3) After completing their flight license training, flight trainees return to the university to continue their relevant course work, theoretical training, and examination for the Airline Transport Pilot License, and defend their undergraduate graduation design (thesis).
After completing the aforementioned stages, the flight trainees are eligible to join corresponding airlines as official civil aviation pilots. Those who fulfill the graduation requirements receive an undergraduate diploma and bachelor’s degree certificate in flight technology from NUAA.
2.2. Simulator and Scenarios
2.2.1. Experimental Equipment
The flight trainer is equipped with several advanced features, including a mechanical joystick and foot rudder, providing a realistic and tactile flight control experience. Moreover, it consists of a flight operation panel that integrates various components such as the ignition key, light switch panel, throttle lever, fuel–air mixing lever, leveling wheels, flaps, and fuel tank selector switch. These components control the simulated flight operations, ensuring a comprehensive and immersive training experience for trainees. The flight simulation equipment is depicted in
Figure 1.
Additionally, the simulation flight trainer is equipped with an integrated avionics system (GARMIN 1000, Kansas City, MO, USA) and a primary flight display (PFD) panel. This avionics system can accurately monitor instruments and navigation data during the flight simulation. The designed avionics system helps flight trainees in developing their skills during simulated flight scenarios. Overall, the incorporation of these advanced features within the flight trainer enables trainees to acquire hands-on experience with the operational aspects of flight controls and avionics systems typically used in aircraft.
2.2.2. Experimental Flight Subject
Based on the comprehensive literature survey and consultation with senior flight instructors, this project selected airfield traffic patterns for flight simulation. It is worth noting that the airfield traffic pattern is a vital component of pilot training, as it involves flying maneuvers around airports. In this training scenario, pilots acquire skills such as takeoff, climb, turning, leveling off, descent, and landing.
Figure 2 illustrates the schematic of an airfield traffic pattern.
In order to evaluate the operational accuracy of the flight simulation, the operational accuracy score of each pilot throughout the flight was obtained based on the simulated airfield traffic pattern rating scale, with a full item score of 98. This score not only reflects the pilot’s operational level for given scenarios of a flight but also enables training focusing on the weak points.
2.3. Procedure
The experiment was conducted using a Cessna C172SP Skyhawk airplane. The tests were carried out on runway 19 at Beijing Capital International Airport. During the tests, the sky was clear with increasing side winds between the ground and 3000 feet, ranging from 5 to 15 knots. To prevent competitors from using abnormal operational methods, the following actions should be implemented: disabling the auto rudder in hard mode (which controls the course), enabling the display flight tips, activating the auto mixer (to adjust the mixture ratio of oil and gas), and enabling the spiral effect (which is a side effect of the propeller, causing left yaw moment due to the propeller turning to the right, particularly noticeable at low speed). Other options and functions were disabled during the test. With the evaluation software turned on, the pilot flew the airplane through an airfield traffic pattern to the left before landing and stopping on the runway. The maximum flight time was 12 min, and the scoring software discarded the results if the flight time was exceeded or if pilots slipped off the runway. If the system determined that the aircraft was damaged, or it could not operate normally due to structural damage, the competition result was discarded and a score of 0 points was recorded. The scoring items and codes are presented in
Table 2.
3. Methodology
The present study proposes a new hybrid algorithm for the feature selection of civil aviation flight training, which incorporates the gradient boosting decision tree and multilayer perceptron. First, the training data are screened to select feature importance using the gradient boosting decision tree (GBDT) model. Then, the screened features are introduced to the multilayer perceptron model for training. Finally, flight training data are classified for each trainee.
3.1. Gradient Boosting Decision Tree Algorithm
GBDT is an integrated learning model, which is classified as a decision tree algorithm based on iterative accumulation. This model constructs a set of weak learning trees and accumulates the results of multiple decision trees as the final prediction result. The role of integrated learning is to enhance these multiple weak learners into one strong learner to minimize error rates. A weak learner typically refers to a single decision tree model constructed in each iteration, while a strong learner refers to the decision tree model constructed at each stage. The model structure of integrated learning is shown in
Figure 3:
When establishing a GBDT model, an initialized regression tree is initially trained on the training dataset, and more regression trees are generated by iterating on this base. Finally, all data are combined into a strong learner.
The main steps of the GBDT model construction are as follows:
- (1)
Weak learner initialization
- (2)
Calculate the negative gradient for each sample
- (3)
The negative gradient obtained in step (2) is used as the new true value of the sample, and is used as the training data for the next tree. Then, a new regression tree is obtained and its corresponding leaf node region is , where J is the number of leaf nodes of regression tree t.
- (4)
Calculate the best-fit value for the leaf region
- (5)
Update to the strong learner
- (6)
Finally, obtain a strong learner
3.2. PSO-CNN Model
3.2.1. Particle Swarm Optimization
Particle swarm optimization (PSO) originates from the observation of bird flock feeding behavior, and its main idea involves seeking the optimal solution through collaboration and information sharing among individuals within a group. The initial state of PSO is a group of random particles. Through iterative processes, the algorithm refines and converges towards the optimal solution. PSO can be mathematically expressed in the form below:
where
i = 1,2,3…
N,
N is the total number of particles;
vi is the velocity of the particle; rand() is a random number between (0,1);
xi is the current position of the particle;
c1 and
c2 are the learning factors, which are usually set to 2 [
21]; and pbest and gbest are the two extremes that the particle needs to track.
The particle determines its next movement based on its individual experience and insights gained from the best-performing peers. The combination of these principles constitutes the standard form of PSO.
3.2.2. Convolutional Neural Network
A convolutional neural network is a type of feedforward neural network with a network computing function, which mainly comprises the convolutional layer, pooling layer, and fully connected layer.
3.3. GBDT-PSO-CNN Model
The present study performs feature selection on flight training data using the GBDT-PSO-CNN hybrid model. In the model, the important features in flight training data by GBDT are trained and predicted by PSO-CNN. The structure of the model is presented in
Figure 4.
In the GBDT-PSO-CNN model, feature importance selection is initially performed using the GBDT model through the following steps:
(1) Calculate the reduction in weighted impurity of all non-leaf nodes at splitting. The higher the reduction degree, the higher the importance of the feature.
(2) The reduction in weighted impurity is the gain of that node for this split. Therefore, the greater the benefit of node splitting, the higher the importance of the corresponding characteristics of the node.
After selecting the important features, they are trained using a PSO-CNN model. The convolutional layer contains multiple convolutional kernels, which cover an area called the “sensory field”; the pooling layer is used for feature selection to reduce the number of features in the input data; and the fully connected layer is used to nonlinearly fit the extracted features to the output.
In summary, the model introduced in this study initially filters out the important features of the data using the GBDT algorithm and subsequently employs a convolutional neural network optimized by the PSO algorithm to classify the target values. Applying the GBDT-PSO-CNN hybrid model effectively reduces the number of features of the data, thereby improving faster training and more accurate predictions.
5. Conclusions
In this research, a hybrid GBDT-PSO-CNN model is proposed. Initially, the GBDT algorithm was employed to extract features from the flight data related to the airport traffic patterns in simulated flights. By analyzing 114 simulated flight data points, crucial features of the airport traffic patterns were identified. Subsequently, a convolutional neural network optimized by the PSO algorithm was used to train the processed data. The recognition accuracy on the test dataset was 93.9% after 300 training cycles on the training set. This performance outperforms similar algorithms in terms of recognition accuracy and resilience, effectively assessing the trainees’ flight simulation competency. The model proposed in this paper mainly implements the following features:
(1) The model has the ability to evaluate the flying performance of flight trainees using flight data with significant features, allowing for the rapid and accurate selection of appropriate flight trainees.
(2) The study’s findings offer empirical evidence to improve trainees’ simulated flight training, and by using the methodology proposed in this study, weaknesses in flight can be quickly and effectively identified for targeted training.
The hybrid model proposed in this study exhibits promising performance for effectively screening suitable flight trainees such as recruiting new members for a flight simulation team or selecting participants for flight simulation competitions. Through the proposed method, flight trainees’ simulation performance weaknesses may be found, enabling more focused instruction. This identification approach effectively evaluates the flight skills of trainees, which in turn guarantees the security and dependability of their subsequent flights.