An Anthropometric Analysis of Korean Male Helicopter Pilots for Helicopter

Transcription

1 An Anthropometric Analysis of Korean Male Helicopter Pilots for Helicopter Cockpit Design Wonsup Lee, Kihyo Jung, Jeongrim Jeong, Jangwoon Park, Jayoung Cho, Heeeun Kim, Seikwon Park, and Heecheon You * * Corresponding author Wonsup Lee; Pohang University of Science and Technology; San 31 Hyoja-dong, Nam-gu, Pohang, Kyungbuk, , Republic of Korea; Tel , Fax: , mcury@postech.ac.kr Kihyo Jung; University of Ulsan; 93 Daehak-ro, Nam-gu, Ulsan, , Republic of Korea; Tel , Fax: , kjung@ulsan.ac.kr Jeongrim Jeong, Loughborough University, Address: James France bldg, Loughborough Design School, Loughborough University, Leicestershire, LE11 3TU, UK; Tel.: , cha_cha_@hanmail.net Jangwoon Park; Pohang University of Science and Technology; San 31 Hyoja-dong, Nam-gu, Pohang, Kyungbuk, , Republic of Korea; Tel , Fax: , parkjw@posteach.ac.kr Jayoung Cho; Korea Research Institute for Fashion Industry; Bongmu-dong, Dong-gu, Daegu, , Republic of Korea; Tel: , Fax:

2 6344, Heeeun Kim; Kyungpook National University; 1370 Sankyunk-dong, Buk-gu, Daegu, , Republic of Korea; Tel , Fax: , Seikwon Park; Korea Air Force Academy; PO Box 335-2, Cheongwon, Choongbuk, , Republic of Korea; Tel , Fax: , Heecheon You; Pohang University of Science and Technology; San 31 Hyoja-dong, Nam-gu, Pohang, Kyungbuk, , Republic of Korea; Tel , Fax: ,

3 An Anthropometric Analysis of Korean Male Helicopter Pilots for Helicopter Cockpit Design Anthropometric Analysis of Pilots Abstract The present study measured 21 anthropometric dimensions (ADs) of 94 Korean male helicopter pilots in their 20s to 40s and compared them with corresponding measurements of Korean male civilians and the US Army male personnel. The ADs and the sample size of the anthropometric survey were determined by a four-step process: (1) selection of ADs related to helicopter cockpit design, (2) evaluation of the importance of each AD, (3) calculation of required sample sizes for selected precision levels, and (4) determination of an appropriate sample size by considering both the AD importance evaluation results and the sample size requirements. The anthropometric comparison reveals that the Korean helicopter pilots are larger (ratio of means = 1.01 ~ 1.08) and less dispersed (ratio of SDs = 0.71 ~ 0.93) than the civilians and that they are shorter in stature (0.99), upper limbs (0.89 ~ 0.96), and lower limbs (0.93 ~ 0.97), but taller in sitting height, sitting eye height, and acromial height (1.01 ~ 1.03), and less dispersed (0.68 to 0.97) than the US Army personnel. Keywords: anthropometric measurement, Korean male helicopter pilots, helicopter cockpit design, sample size determination

4 Practitioner Summary The anthropometric characteristics of Korean male helicopter pilots were compared with those of Korean male civilians and US Army male personnel. The sample size determination process and the anthropometric comparison results presented in this study are useful to design an anthropometric survey and a helicopter cockpit layout, respectively.

5 1. Introduction Anthropometric data of pilots have been utilized for the design of an aircraft cockpit for comfort of pilots and effectiveness of mission fulfillment. Roebuck et al. (1975) and Roskam (2002) provided a method to design a cockpit layout using anthropometric data and recommended values on selected design dimensions such as the locations of the design eye point and the cyclic control in a helicopter cockpit. Military standards such as MIL-STD-1333B (Department of Defense, 1987) also specified ergonomics design requirements of a helicopter cockpit for the aircrew personnel of the US Army to help pilots accomplish operations with efficiency, safety, and comfort. A customized survey and an in-depth analysis of anthropometric data are needed to develop an ergonomics helicopter cockpit design which properly accommodates a designated user population. The South Korean government launched the Korean helicopter program (KHP) in 2006 to develop a utility helicopter that would be operationalized in the Korean Army by 2013 (Defense Acquisition Program Administrator, 2010). Although an anthropometric database of Korean civilians (n = 21,295) compiled at the nation-wide Size Korea 2004 project (Korean Agency for Technology and Standards, 2004) is available, its applicability to helicopter cockpit

6 design for the Korean Army may be limited because the anthropometric characteristics of the Korean civilian population can be significantly different from those of the Korean helicopter pilot population due to occupational factors (Roebuck, 1995, Sanders and McCormick, 1998). Moreover, there is a need to understand the differences in anthropometric features between the Korean helicopter pilots and the US Army personnel (Gordon et al., 1988) for the design of a helicopter cockpit for the KHP (Jung et al., 2008). Although the Korean utility helicopter is being developed primarily for Korean helicopter pilots, the KHP includes a plan to export helicopters to overseas markets. The anthropometric data of the US Army personnel was utilized in the present study for its data accessibility and ethnic diversity of the US population. The present study is intended to examine the anthropometric characteristics of Korean helicopter pilots to develop an ergonomics design of a utility helicopter cockpit. Anthropometric measurements were collected from 94 Korean male helicopter pilots and compared with those of Korean male civilians and the US Army male personnel. 2. Anthropometric Survey Method

7 2.1. Anthropometric Dimension Selection and Importance Evaluation Twenty-one anthropometric dimensions (ADs; see Table 1 and Figure 1) were selected as those related to the design of a cockpit layout. A panel of five experts (two ergonomists, two mechanical engineers, and one fighter pilot) reviewed literature and evaluated the importance of each AD in designing a cockpit layout. The literature review included studies of ergonomics workstation layout designs such as Bittner (2000), Kim and Whang (1997), Lee and Song (2002), You et al. (1997), and Zehner et al. (1999). For example, sitting height (AD3) and sitting eye height (AD4) were selected because they are related to head clearance and design eye point position, respectively, in a cockpit layout design. Next, the importance of an individual AD in designing a cockpit layout was assessed using a 3-categorical scale (high, medium, and low). For example, the importance of buttock-to-popliteal length (AD16) was rated as high because it strongly affects the seat length in a cockpit, while that of chest depth (AD8) was determined as low because it weakly affects the design of a cockpit layout. The AD importance evaluation results were applied in the present study to situations where a trade-off between precision and practical constraints needed to be compromised in sample size determination.

8 [Table 1 about here] [Figure 1 about here] 2.2. Sample Size Determination The sample size of the anthropometric survey was determined in two steps: (1) statistical sample size requirement analysis and (2) sample size selection by considering the AD importance evaluation results and practical constraints. First, the sample sizes of the ADs required for the confidence level (1-α) of 95% and four precision levels (k = 2%, 3%, 4%, and 5%) were calculated as displayed in Figure 2 by Equation 1 of sample size formula (ISO, 2006): [Figure 2 about here] CV = ( 1.96 ) k 2 2 n (Equation 1) where: CV = coefficient of variation, k = precision level The precision level (k) refers to the ratio of a sampling error to the corresponding

9 sample mean. For example, 2% of precision level when the sample mean of stature = 170 cm means 3.4 cm (= ) of sampling error in estimating the corresponding population mean with a selected confidence level. Coefficient of variance (CV) is calculated by dividing SD with mean. The mean and SD of each AD of the Korean male helicopter pilot population in their 20s to 40s were estimated using Equations 2 and 3 (derived in the present study) and corresponding descriptive statistics reported for each age group (20 ~ 24, 25 ~ 29, 30 ~ 34, 35 ~ 39, 40 ~ 44, and 45 ~ 49) in the 2004 Size Korea survey results: X j i i= 1 = j X n i= 1 n i i (Equation 2) where: X = sample mean of a composite population, X = sample mean of population i, i n i = sample size of population i j = the number of populations j 2 2 [ ni X i + ( ni 1) si ] 2 ni X i= 1 i= 1 s = j (Equation 3) n 1 i= 1 i j

10 j [ pi ( X i + si )] X i= 1 where: s = sample SD of a composite population, X = sample mean of a composite population, X i = sample mean of population i, s i = sample standard deviation of population i, n i = sample size of population i p = proportion of population i i j = the number of populations For example, the mean and SD of shoulder-to-elbow length (AD13) of the Korean helicopter pilot population were estimated as 33.8 cm and 1.5 cm, respectively, using the corresponding means and sample SDs of the Korean male civilian data in their 20s to 40s. As shown in Figure 2, a sample size requirement geometrically increases as the level of precision becomes high; for example, the sample size requirements of thumb-tip reach (AD14) are 9 for k = 5%, 14 for k = 4%, 24 for k = 3%, and 54 for k = 2%. The present study determined 94 as the sample size for the Korean helicopter pilot anthropometric survey by accommodating the AD importance evaluation results,

11 sample size requirement analysis results, and practical considerations. Out of the sample size requirement analysis results, the AD importance analysis results were further considered. Then, the sampling errors of the ADs having high importance for the three precision levels were calculated and k = 2% (maximum sampling error = 1.9 cm in popliteal height) was found acceptable in the cockpit design process. Finally, of the sample size requirement results for k = 2% (high importance) and k = 5% (medium and low importance), the largest value was used to determine the sample size of the helicopter pilot anthropometric survey. Lastly, the present study reports the anthropometric data of Korean male helicopter pilots due to a very small number of Korean female helicopter pilots (n < 10) commissioned in the Army (Jung et al., 2008). We measured six female pilots, but their measurements are not reported in this paper due to their small sample size Measurement Protocol Anthropometric measurements of the selected ADs were collected by following corresponding standard measurement protocols. Measurement locations and landmarks for the ADs were identified as illustrated in Figure 1 by referring to Gordon et al. (1988) and Korean Standard Association (2005). A Martin-type anthropometer (Takei Co.,

12 Japan) and aids such as a chair, a foot-rest, and a grid board were utilized during measurement. Two measurements were collected for each AD, but additional measurements were made until the difference between two measurements < 2 mm (Jung et al., 2008). Then, the average of each pair of measurements was entered into a computer program coded in the present study; the computer program checks the validity of an input value (x) by classifying it into one of three categories based on corresponding mean and SD from the Size Korea 2004 data: normal, x mean 3 SD; cautionary, 3 SD < x- mean 5 SD; abnormal, x- mean > 5 SD (Jung et al., 2008). Proper actions such as checking the validity of data and correcting typos were taken if a validity level of measurement was cautionary or abnormal Statistical Testing The population of Korean male helicopter pilots was compared with those of Korean male civilians and US Army male personnel by a two-sample t test for comparison of means and an F test for comparison of variances using MINITAB v. 12. The Size Korea data of Korean male civilians (Korean Agency for Technology and Standards, 2004) and the 1988 anthropometric survey of US Army personnel (Gordon et al., 1988) were utilized in the present study for comparison purposes.

13 3. Results Anthropometric measurements were collected from 94 Korean male helicopter pilots and their descriptive statistics (mean, SD, min, max, and percentiles) on the anthropometric measurements summarized in Table 2. For example, the average of eye height (AD4; unit: cm) of the Korean male helicopter pilots is 81.3 (SD = 3.0), ranging from 74.0 to 89.0 with p.01 = 74.2, p.05 = 76.8, p.95 = 86.7, and p.99 = The sample size (n = 94) measured for the Korean helicopter pilot was found to be sufficient. Post-hoc analysis on the sample size revealed that the required sample sizes of ADs at the designated level of confidence (95%) and precision (2% for high importance ADs; 5% for medium and low importance ADs) were 66 or less. [Table 2 about here] A comparison in mean and SD between the Korean male helicopter pilots and Korean male civilians (Table 3) revealed that the helicopter pilots were larger (ratio of

14 means = 1.01 ~ 1.08) and less dispersed (ratio of SDs = 0.71 ~ 0.93) overall. Out of the 21 ADs, 19 ADs were available in the Size Korea data for comparison. The helicopter pilots were found statistically larger at α =.05 in all of the ADs and a relatively large mean difference (ratio of means > 1.07) was observed in hip breadth and thigh clearance. Next, the helicopter pilots were found less dispersed in all of the ADs but a statistically significant difference in SD at α =.05 (ratio of SDs < 0.84) was observed in 14 ADs (stature, weight, sitting height, biacromial breadth, chest circumference, waist circumference, elbow-to-fingertip length, forearm-to-forearm breadth, shoulder-toelbow length, buttock-to-popliteal length, foot length, knee height, popliteal height, thigh circumference, and thigh clearance). [Table 3 about here] Lastly, a comparison in mean and SD between the Korean male helicopter pilots and the US Army male personnel (Table 3) showed that the Korean helicopter pilots were shorter in stature (ratio of means = 0.99), upper limbs (0.89 ~ 0.96), and lower limbs (0.93 ~ 0.97), but longer in head and trunk (1.01 ~ 1.03), leaner (0.93 ~ 0.98 in weight and circumference dimensions), and less dispersed in all of the ADs

15 (ratio of SDs = 0.68 ~ 0.97). Out of the 21 ADs, 20 ADs were available in the US Army data for comparison. Table 3 shows that the Korean helicopter pilots had shorter body sizes (ratio of means = 0.93 ~ 0.99) than the US Army personnel except for the head and trunk related ADs (sitting height, sitting eye height, and sitting acromial height) and the dispersions of the body sizes of the Korean helicopter pilots were considerably smaller (ratio of SDs = 0.68 ~ 0.97) than those of the US Army personnel overall. 4. Discussion The present study collected anthropometric data of Korean helicopter pilots to design a helicopter cockpit layout. A comprehensive literature review was conducted to select ADs in four body categories (whole body, head & trunk, upper limbs, and lower limbs) which are applicable to the design of a helicopter cockpit layout. The anthropometric data of helicopter pilots compiled in the study was effectively used together with the US Army data in the design and evaluation phases of helicopter cockpit development for Korean helicopter pilots, which were conducted as a follow-up study by the authors as illustrated in Figure 3.

16 [Figure 3 about here] Human errors which may occur in reading or recording measurements could be systematically prevented by checking the difference between repeated measurements and comparing a key entry with corresponding statistical data obtained from a national anthropometric survey. Repeated measurements were collected until their difference reached less than 2 mm to avoid an error in measurement due to misreading and/or application of an inconsistent measurement protocol. Then, the validity of each key entry was checked using its standardized score a recheck of an input value was made if the standardized score > 3. The sample size of the anthropometric survey for Korean helicopter pilots was determined as 94 in the present study by incorporating statistical and practical considerations. First, a statistical analysis was conducted to identify a sample size requirement for each of the ADs for a designated level of confidence and various levels of precision using the corresponding sample mean and sample SD. The sample SD formula for a composite population was derived in the present study to estimate a pooled sample SD using SDs of subpopulations. Next, out of the sample size

17 requirement analysis results, ADs identified as high importance were considered for effective utilization of limited resources in the study. Then, the acceptable level of precision in helicopter cockpit layout design was identified by evaluating sampling errors at different precision levels. Finally, the sample size of the helicopter pilot anthropometric survey was determined for the selected precision level (k = 0.02 for high importance ADs, k = 0.05 for medium and low importance ADs) among the sample size requirements of the ADs. The aforementioned sample size determination process is applicable to identify a proper sample size by considering statistical and practical requirements. The Korean male helicopter pilots showed a higher level of homogeneity in all the ADs than Korean male civilians and the US Army male personnel. Demographic factors such as occupation, age, and race significantly affect the variability of an AD (Roebuck, 1995). The difference in SD (ratio of SDs = 0.71 ~ 0.93) between the Korean pilots and Korean civilians can be mainly explained by occupational diversity, while that (ratio of SDs = 0.68 ~ 0.97) between the Korean pilots and the US Army personnel by racial diversity. It is also noticeable that Korean civilians are more homogenous than the US Army overall. The higher the homogeneity indicates the lower the adjustability required for a cockpit layout design, the smaller the space required for a cockpit, the

18 lighter the weight of the helicopter, and the higher the air combat performance of the helicopter. The Korean helicopter pilots were found larger than Korean civilians in all the ADs. The body sizes of a particular population can be influenced by occupational factors such as selection and training (Wickens et al., 1998). It is likely that Korean pilots are larger than Korean civilians due to physical requirements (height, weight, and physical fitness) for pilots, military training, and self-management of pilots for physical fitness. The Korean helicopter pilots were found shorter in stature, upper-limbs, and lower-limbs and smaller in weight, body circumference, and thickness than the US Army personnel, but longer in upper-body heights such as sitting height, sitting eye height, and acromial height. The former ADs affect the clearance and reach of a cockpit layout design, while the latter affect the visibility of the layout design. These distinctive features of the Korean helicopter pilots compared with the US Army personnel support the necessity of an anthropometric survey on a target user population to develop an optimal, customized design. Lastly, the present study has limitations in terms of availability of female pilot data and application of secular trend analysis. Due to a small number of Korean female

19 helicopter pilots (n < 10) when the present anthropometric survey was conducted, their anthropometric characteristics were not formally reported. An anthropometric survey can be planned in the future as the number of Korean female pilots becomes sufficiently large. Next, the anthropometric characteristics of the US Army personnel are likely to have changed over last 25 years (Tomkinson et al., 2010). Adjustments should have been made to the US Army anthropometric data based on a secular trend analysis for better comparison with those of Korean helicopter pilots collected relatively recently.

20 Acknowledgments This research was jointly supported by Korea Helicopter Program (KHP) grant funded by Korea Aerospace Industries (KAI) and Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (R ). The authors appreciate the assistance of Jeeeun Park in anthropometric measurement. References Bittner, A.C., A-CADRE: Advanced family of manikins for workstation design. In: Proceedings of Proceedings of the Human Factors and Ergonomics Society 44th Annual Meeting, San Diego: CA: Human Factors and Ergonomics Society. Defense Acquisition Program Administrator, Introduction to KHP project (in Korean) [online]. Available from: group.jsp [Accessed 26 March 2010]. Department of Defense, Aircrew Station Geometry for Military Aircraft, MIL- STD-1333B, Washington, DC. Gordon, C.C., Bradtmiller, B., Churchill, Y., et al., Anthropometric Survey of US Army Personnel: Methods and Summary Statistics, NATICK/TR-89/044, Natick, MA: US Army Natick Research Center. ISO, General Requirements for Establishing Anthropometric Databases, ISO 15535, Geneva, Switzerland: International Standards Organisation. Jung, K., Cho, J., Jung, J., et al., Anthropometric analysis of Korean helicopter pilots for helicopter cockpit design. Journal of the Ergonomics Society of Korea, 27 (4),

21 Kim, J. and Whang, M., Development of a set of Korean manikins. Applied Ergonomics, 28 (5), Korean Agency for Technology and Standards, The Fifth Report on Korean Anthropometric Measurements, Seoul, Korea: Size Korea, Ministry of Knowledge Economy. Korean Standard Association, General Requirements for Establishing Anthropometric Databases, KS-A-ISO 15535, Seoul, Korea. Lee, J. and Song, Y., Formulation of human manikin models representative of Korean male pilots. Journal of the Ergonomics Society of Korea, 21 (1), Roebuck, J.A., Anthropometric Methods: Designing to Fit the Human Body. Santa Monica, CA: Human Factors and Ergonomics Society. Roebuck, J.A., Kroemer, K.H.E. and Thomson, W.G., Engineering Anthropometry Methods. New York, NY: John Wiley & Sons. Roskam, J., Airplane Design Part III: Layout Design of Cockpit, Fuselage, Wing, and Empennage: Cutaways and Inboard Profiles. Lawrence, KS: DAR Corporation. Sanders, M.S. and McCormick, E.J., Human Factors in Engineering and Design, 7th ed. New York, NY: McGraw-Hill. Tomkinson, G.R., Clark, A.J. and Blanchonette, P., Secular changes in body dimensions of Royal Australian Air Force aircrew ( ). Ergonomics, 53 (8), Wickens, C.D., Gordon, S.E. and Liu, Y., An Introduction to Human Factor Engineering. New York, NY: Addison-Wesley. You, H., Bucciaglia, J., Lowe, B.D., et al., An ergonomic design process for a US transit bus operator workstation. Heavy Vehicle Systems, A Series of the International Journal of Vehicle Design, 4 (2-4), Zehner, G.F., Kennedy, K.W. and Hudson, J.A., Anthropometric accommodation in the T-38. Safe Journal, 29 (1),

22 List of Tables Table 1. Anthropometric dimensions (ADs) and their importance in helicopter cockpit layout design Table 2. Descriptive statistics of Korean male helicopter pilot anthropometric data Table 3. Comparison of Korean male helicopter pilots, Korean male civilians, and US Army male personnel List of Figures Figure 1. Anthropometric dimensions (ADs) measured for helicopter cockpit layout design Figure 2. Sample size requirements by precision Figure 3. Ergonomics evaluation of a helicopter cockpit for Korean helicopter pilots

23 Table 1. Anthropometric dimensions (ADs) and their importance in helicopter cockpit layout design Importance (H: high; M: medium; L: low) AD1 Stature M AD2 Weight L AD3 Sitting height H AD4 Sitting eye height H AD5 Sitting acromial height H AD6 Biacromial breadth M AD7 Chest circumference L AD8 Chest depth L AD9 Hip breadth H AD10 Waist circumference L AD11 Elbow-to-fingertip length H AD12 Forearm-to-forearm breadth M AD13 Shoulder-to-elbow length H AD14 Thumb-tip reach H AD15 Buttock-to-knee length H AD16 Buttock-to-popliteal length H AD17 Foot length L AD18 Knee height H AD19 Popliteal height H AD20 Thigh circumference L AD21 Thigh clearance L Body part Code Anthropometric dimension Whole body Head & trunk Upper limbs Lower limbs

24 Table 2. Descriptive statistics of Korean male helicopter pilot anthropometric data (unit: cm, kg) Percentile Body part Anthropometric dimension (AD) Mean SD Min Max 1 st 5 th 95 th 99 th Whole body AD1 Stature AD2 Weight AD3 Sitting height AD4 Sitting eye height AD5 Sitting acromial height Head & trunk AD6 Biacromial breadth AD7 Chest circumference AD8 Chest depth AD9 Hip breadth AD10 Waist circumference AD11 Elbow-to-fingertip length Upper limbs AD12 Forearm-to-forearm breadth AD13 Shoulder-to-elbow length AD14 Thumb-tip reach AD15 Buttock-to-knee length AD16 Buttock-to-popliteal length AD17 Foot length Lower limbs AD18 Knee height AD19 Popliteal height AD20 Thigh circumference AD21 Thigh clearance

25 Table 3. Comparison of Korean male helicopter pilots, Korean male civilians, and US Army male personnel (unit: cm, kg) Body part Anthropometric dimension (AD) Korean helicopter pilots (KP; n = 94) Korean civilians (KC; n = 1800) KP vs. KC US Army (UA; n = 1774) KP vs. UA M KP SD KP M KC SD KC M KP - KC M KP /M KC SD KP / SD KC M UA SD UA M KP -UA M KP /M UA SD KP / SD UA Whole body AD1 Stature ** ** ** ** AD2 Weight ** * ** ** AD3 Sitting height ** * ** ** AD4 Sitting eye height ** ** AD5 Sitting acromial height ** ** Head & trunk AD6 Biacromial breadth ** ** * AD7 Chest circumference ** ** ** ** AD8 Chest depth N/C N/C N/C N/C N/C N/C AD9 Hip breadth ** ** ** AD10 Waist circumference ** ** ** ** AD11 Elbow-to-fingertip length ** ** ** ** Upper limbs AD12 Forearm-to-forearm breadth ** * ** AD13 Shoulder-to-elbow length ** * ** ** AD14 Thumb-tip reach N/A N/A N/A N/A N/A ** ** AD15 Buttock-to-knee length ** ** ** AD16 Buttock-to-popliteal length ** ** ** ** AD17 Foot length ** ** ** ** Lower limbs AD18 Knee height ** * ** ** AD19 Popliteal height ** ** ** ** AD20 Thigh circumference ** ** ** ** AD21 Thigh clearance ** ** * P <.05; ** P <.01; N/C: not comparable due to use of different landmarks; N/A: not available

26 A AD6 A AD7 AD14 AD1 AD10 AD20 A AD3 AD4 AD13 AD8 AD5 B AD12 AD11 AD21 C AD9 AD16 AD15 AD19 AD18 AD17 (Notes) 1. Landmarks: A: acromion, B: rear olecranon, C: superior patella 2. Refer to Table 1 for the names of AD codes. Figure 1. Anthropometric dimensions (ADs) measured for helicopter cockpit layout design

27 Sample size k = 0.02 k = 0.03 k = 0.04 k = Level of importance High Medium Low (Notes) 1. Refer to Table 1 for the names of AD codes. 2. The sample size requirement of AD14 (thumb-tip reach) was estimated using the US Army data due to its unavailability in the Korean civilian data. Figure 2. Sample size requirements by precision

28 (a) Visibility evaluation with a virtual mockup (b) Head clearance evaluation with a physical mockup (c) Usability evaluation with a physical mockup Figure 3. Ergonomic evaluation of a helicopter cockpit for Korean helicopter pilots